CN100428520C - Electric switch and storage device using same - Google Patents

Electric switch and storage device using same Download PDF

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CN100428520C
CN100428520C CNB2004800124719A CN200480012471A CN100428520C CN 100428520 C CN100428520 C CN 100428520C CN B2004800124719 A CNB2004800124719 A CN B2004800124719A CN 200480012471 A CN200480012471 A CN 200480012471A CN 100428520 C CN100428520 C CN 100428520C
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ferroelectric substrate
electric switch
electric field
polarization
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CN1784793A (en
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水内公典
山本和久
杉田知也
森川显洋
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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Abstract

Comprising: a ferroelectric substrate to which metal is added, a pair of electrodes provided on the ferroelectric substrate, and an electric field applying portion for changing the direction of polarization in part of the ferroelectric substrate.

Description

Electric switch and use the memory element of this electric switch
Technical field
The present invention relates to utilize conductivity along with the variation of the spontaneous polarization of ferroelectric (ferroelectric) electric switch that changes and the memory element that uses this electric switch.
Background technology
Ferroelectric has spontaneous polarization, can carry out the control of polarised direction.Variable device as utilizing ferroelectric spontaneous polarization has ferroelectric memory.It is to utilize by ferroelectric is applied the direction that voltage changes spontaneous polarization, the characteristic that electric charge moves thereupon, constitutes electric switch, is used as nonvolatile memory.In this ferroelectric memory, known that the variation of the conductivity that is accompanied by the spontaneous polarization variation is the generation reason of leakage current, as the leakage current countermeasure, prevent that the method that conductivity changes is studied.In addition, utilize the technology (with reference to Japanese kokai publication hei 10-56141 communique) of leakage current in addition.In addition, as the device that utilizes ferroelectric polarization, have and for example utilize the electric switch that makes the characteristic of electrical conductivity variation by overcurrent.
In addition, about ferroelectric polarization, have at the Mg of X plate Li doped NbO 3The report of middle polarization inversion unit demonstration rectification characteristic, low resistanceization (with reference to S.Sonoda, I.Tsumura, and M.Hatori; Applied Physics Letters, vol.70, pp.3078-3079,1997).
In addition, also have by in ferroelectric, flow through the electric switch that overcurrent changes electrical conductivity (with reference to Y.Watanabe, J.G.Bdxorz, A.Biestsch, Ch.Gerber, D.Widmer, A.Beck; Applied Physics Letters, vol.78, pp.3738-3740,2001).
Like this, the various technology of utilizing ferroelectric polarization are arranged.In addition, in ferroelectric memory, the phenomenon of its insulating properties variation along with the variation of spontaneous polarization is the phenomenon that makes the characteristic variation of ferroelectric memory, but these characteristics are about several times～variation of several about 10 times conductivity.
It is good utilizing stability, production and the reliability of the ferroelectric memory that the existing market of the variation of ferroelectric spontaneous polarization sells, and this is proved by memory application widely.But ferroelectric memory in the past is with moving the electric field that produces by the electric charge that is accompanied by the spontaneous polarization counter-rotating, as the voltage that drives semiconductor switch, is 2 times.The limited problem of raising that therefore, complex structure, integrated level are arranged.And then it is enough good to say so at aspects such as holding time of the number of repetition of life-span of memory, switch and non-volatile electric charge.On the other hand, though,, also do not realize owing to do not find suitable ferroelectric material to directly utilizing the variation of spontaneous polarization itself to attempt in the switch yet.
Summary of the invention
The present invention puts in view of the above problems and makes, and purpose provides a kind of simple in structure, ferroelectric electric switch that integrated level is high and uses its memory element.
Electric switch of the present invention is characterised in that to have: the ferroelectric substrate that has added metal; Be arranged on the pair of electrodes on the above-mentioned ferroelectric substrate; The electric field applying unit that the polarised direction of the part of above-mentioned ferroelectric substrate is changed; By above-mentioned polarised direction is changed, make the resistance change of above-mentioned ferroelectric substrate.
Memory element of the present invention is characterised in that to have a plurality of electric switches of the present invention; The resistance value that is keeping the above-mentioned ferroelectric substrate of above-mentioned each electric switch.
Description of drawings
Figure 1A is the stereogram of structure of the electric switch of expression embodiments of the present invention 1.
Figure 1B is the stereogram of structure of the another kind of electric switch of expression embodiments of the present invention 1.
Fig. 2 A is the figure that is used for illustrating the polarised direction when the ferroelectric substrate applied voltage.
Fig. 2 B is the figure that is used for illustrating the polarised direction when the ferroelectric substrate applied voltage.
Fig. 2 C is the figure that is used for illustrating the polarised direction when the ferroelectric substrate applied voltage.
Fig. 2 D is the electric field of the hysteresis characteristic of expression when the ferroelectric substrate applied voltage and the graph of a relation of polarization.
The current-voltage characteristic separately of the state shown in the state shown in Fig. 3 presentation graphs 2A and Fig. 2 C.
Time and changes in resistance when Fig. 4 A represents that the ferroelectric substrate applied direct voltage.
Fig. 4 B represents the frequency and the changes in resistance of ferroelectric substrate.
Fig. 5 A is the vertical view that is used for illustrating the shape of electrode.
Fig. 5 B represents the length of periphery of each electrode of electrode pair and the relation of resistance.
Fig. 6 A is the end view of structure of the 1st electric switch of expression execution mode 2.
Fig. 6 B is the vertical view of structure of the 2nd electric switch of expression execution mode 2.
Fig. 7 A is the end view of structure of the 3rd electric switch of expression execution mode 2.
Fig. 7 B is illustrated in the electric current mobile between electrode pair and the figure of time relation.
Fig. 8 A is the end view of structure of the 4th electric switch of expression present embodiment 2.
The figure of the relation of Fig. 8 B voltage that to be expression apply the ferroelectric substrate of the 4th electric switch of present embodiment 2 and effluxion.
Fig. 8 C is the figure that is illustrated in the relation of the electric current that flows through in the 4th electric switch of present embodiment 2 and effluxion.
Fig. 9 A is the vertical view of structure of the electric switch of expression embodiments of the present invention 3.
Fig. 9 B is the cutaway view of structure of the electric switch of expression embodiments of the present invention 3.
Fig. 9 C be expression embodiments of the present invention 3 generation the vertical view of structure of electric switch of state of domain wall (domain wall: polarization wall).
Fig. 9 D be expression embodiments of the present invention 3 generation the cutaway view of structure of electric switch of state of domain wall.
Figure 10 is the structure chart of structure of the another kind of electric switch of expression execution mode 3.
Figure 11 A is the vertical view of structure of the 1st electric switch of expression embodiments of the present invention 4.
Figure 11 B is the cutaway view of structure of the 1st electric switch of expression embodiments of the present invention 4.
Figure 11 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 1st domain wall.
Figure 11 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 1st domain wall.
Figure 12 A is the vertical view of structure of the 2nd electric switch of expression embodiments of the present invention 4.
Figure 12 B is the cutaway view of structure of the 2nd electric switch of expression embodiments of the present invention 4.
Figure 12 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 2nd domain wall.
Figure 12 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 2nd domain wall.
Figure 13 A is the vertical view of structure of the 3rd electric switch of expression embodiments of the present invention 4.
Figure 13 B is the cutaway view of structure of the 3rd electric switch of expression embodiments of the present invention 4.
Figure 13 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 3rd domain wall.
Figure 13 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 3rd domain wall.
Figure 14 A is the vertical view of structure of the 4th electric switch of expression embodiments of the present invention 4.
Figure 14 B is the cutaway view of structure of the 4th electric switch of expression embodiments of the present invention 4.
Figure 14 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 4th domain wall.
Figure 14 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 4th domain wall.
Figure 15 A is the vertical view of structure of the 5th electric switch of expression embodiments of the present invention 4.
Figure 15 B is the cutaway view of structure of the 5th electric switch of expression embodiments of the present invention 4.
Figure 15 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 5th domain wall.
Figure 15 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 5th domain wall.
Figure 16 A is the vertical view of structure of the 6th electric switch of expression embodiments of the present invention 4.
Figure 16 B is the cutaway view of structure of the 6th electric switch of expression embodiments of the present invention 4.
Figure 16 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 6th domain wall.
Figure 16 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 6th domain wall.
Figure 17 A is the vertical view of structure of the 7th electric switch of expression embodiments of the present invention 4.
Figure 17 B is the cutaway view of structure of the 7th electric switch of expression embodiments of the present invention 4.
Figure 17 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 7th domain wall.
Figure 17 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 7th domain wall.
Figure 18 A is the vertical view of structure of the 8th electric switch of expression embodiments of the present invention 4.
Figure 18 B is the cutaway view of structure of the 8th electric switch of expression embodiments of the present invention 4.
Figure 18 C be expression embodiments of the present invention 4 generation the vertical view of structure of electric switch of state of the 8th domain wall.
Figure 18 D be expression embodiments of the present invention 4 generation the cutaway view of structure of electric switch of state of the 8th domain wall.
Figure 19 is the electric switch of expression execution mode 5 and the schematic diagram of the structure of the experimental system of measuring it.
Figure 20 A is that to make the ferroelectric substrate be undoped LiNbO 3, the graph of a relation that applies voltage and electric current when making its thickness be 0.15mm.
Figure 20 B is that to make the ferroelectric substrate be the LiNbO of 5mol%Mg of having mixed 3, the graph of a relation that applies electric field and electric current when making its thickness be 1mm.
Figure 21 A is the figure of situation of the polarization of electrode of the state that expression polarization begins to reverse, resistance reduces.
Figure 21 B represents that the polarization reversal of having reversed is reversed again, the figure of the situation of the state polarization of electrode of resistance reinstatement.
Figure 22 is the molar concentration of the Mg that mixes in the ferroelectric substrate and the graph of a relation of interelectrode changes in resistance amount.
Figure 23 A is the figure that expression is accompanied by the interelectrode voltage waveform of effluxion.
Figure 23 B is the figure that expression is accompanied by the interelectrode current waveform of effluxion.
Figure 24 is the stereogram of structure of the memory element of expression execution mode 6.
Figure 25 is the stereogram of structure of specifically representing the memory element of execution mode 6.
Embodiment
Electric switch of the present invention changes ferroelectric electrical conductivity significantly by controlling ferroelectric spontaneous polarization and carries out switch.Thus, because can be with ferroelectric as direct switch, so can realize the higher electric switch of integrated level with simple structure.
In addition, preferably, above-mentioned ferroelectric substrate is an oxide.Thus, the ferroelectric substrate has high-insulativity.Therefore, can realize bigger resistance variations by switch.
In addition, preferably, above-mentioned ferroelectric substrate is made of the ferroelectric material of single polarization, above-mentioned electric field applying unit with the polarised direction of above-mentioned ferroelectric substrate opposed towards on apply electric field.Thus, because the polarised direction unanimity, so can be with the low voltage drive switch.
In addition, preferably, above-mentioned ferroelectric substrate when polarization reversal residual have with above-mentioned counter-rotating after the opposed internal electric field of polarization.Thus, can see the changes in resistance of ferroelectric substrate.
In addition, preferably, above-mentioned electric field applying unit applies electric field to above-mentioned ferroelectric substrate, and above-mentioned electric field is the AC field of frequency more than or equal to 5Hz.Thus, the resistance of ferroelectric substrate does not change along with the time, so be stable.
In addition, preferably, above-mentioned electric field applying unit applies electric field to above-mentioned ferroelectric substrate, and above-mentioned electric field is the high-frequency electric field that superposeed.Thus, can be reduced in and the ferroelectric substrate of low resistanceization is reversed and required electric current during high resistance again.Therefore can reduce the driving electric of electric switch.
In addition, preferably, add above-mentioned metal in the above-mentioned ferroelectric substrate to and be at least a among Mg, Zn, In, Sc, Cu, the Fe, above-mentioned ferroelectric substrate is LiNbO 3Thus, can see the changes in resistance of ferroelectric substrate.
In addition, above-mentioned ferroelectric substrate can be the LiNbO that has added the Z plate of above-mentioned metal 3
In addition, preferably, above-mentioned ferroelectric substrate is the ferroelectric crystallization after single polarization is handled.Thus, because the polarised direction unanimity, so can carry out the driving of switch with low-voltage.
In addition, preferably, above-mentioned ferroelectric substrate is polycrystalline or amorphous (noncrystalline) material.Thus, the ferroelectric substrate can be made film, thus do not need in the mill body (bulk: crystalline growth bulk), can easily make.
In addition, preferably, above-mentioned pair of electrodes is arranged along the direction of the spontaneous polarization of above-mentioned ferroelectric substrate, and above-mentioned electric field applying unit is by applying electric field between above-mentioned pair of electrodes, control the polarised direction of the part of above-mentioned ferroelectric substrate, and control the resistance between above-mentioned pair of electrodes.Thus, constituted electric switch.
In addition, preferably, also has the pair of electrodes that forms roughly arranging on the direction of quadrature with the spontaneous polarization direction of above-mentioned ferroelectric substrate, above-mentioned electric field applying unit is by applying electric field between the pair of electrodes that forms along above-mentioned spontaneous polarization direction arrangement, control the polarised direction of the part of above-mentioned ferroelectric substrate, be controlled at and the spontaneous polarization direction is roughly arranged on the direction of quadrature and resistance between the pair of electrodes that forms.Thus, constituted electric switch.
In addition, preferably, above-mentioned ferroelectric substrate is applied electric field, the polarised direction of 10%～90% part in the above-mentioned ferroelectric part that applies electric field is changed by above-mentioned electric field applying unit.Thus, the resistance value of part of electric field of can having controlled applying of above-mentioned ferroelectric substrate.
In addition, the direction of the spontaneous polarization of above-mentioned ferroelectric substrate can be with respect to the surperficial approximate vertical of above-mentioned ferroelectric substrate.
In addition, the direction of the spontaneous polarization of ferroelectric substrate can be with respect to the surperficial almost parallel of above-mentioned ferroelectric substrate.
In addition, preferably, the maximum resistance of above-mentioned ferroelectric substrate is more than or equal to 100 times of minimum resistance.Thus, had function as electric switch.
In addition, preferably, certain electrode at least of above-mentioned pair of electrodes is a comb poles.Thus, the expansion of polarization reversal accelerates.
In addition, above-mentioned ferroelectric substrate can be the crystallization of single polarization, the Y direction almost parallel of direction that the electrode of above-mentioned comb poles refers to and above-mentioned crystallization.
In addition, preferably, above-mentioned electric field applying unit is by the above-mentioned ferroelectric polarised direction of control, form near between above-mentioned pair of electrodes or elimination as the domain wall in the boundary line of different polarised directions, and change resistance value between above-mentioned pair of electrodes.Thus, can realize electric switch.
In addition, preferably, on the surface of above-mentioned ferroelectric substrate, be formed with groove, in above-mentioned groove, form above-mentioned pair of electrodes.Thus, Electric Field Distribution becomes evenly, has reduced the voltage that is used for driving electric switch.In addition, the influence of surface charge diminishes, and has improved the insulating properties between pair of electrodes.
In addition, preferably, the interpolation concentration of above-mentioned metal is more than or equal to 1mol%.Thus, can access the bigger resistance variations of ferroelectric substrate.
In addition, preferably, the direction of the spontaneous polarization of above-mentioned ferroelectric substrate is with respect to the surface tilt of above-mentioned ferroelectric substrate.That is, this ferroelectric substrate spontaneous polarization direction that is the ferroelectric substrate is cut complementary basis plate (off-cutsubstrate) with respect to what the ferroelectric substrate surface tilted to intersect.Thus, the polarization of ferroelectric substrate is controlled higher.Can reproducibility form uniform polarization reversal well.
In addition, preferably, the surface of above-mentioned ferroelectric substrate is provided with a pair of polarization electrode, and above-mentioned electric field applying unit applies electric field at above-mentioned a pair of polarization electricity consumption interpolar.Thus, owing to can polarizing with electrode and for detection resistance value flows through the electrode of electric current, so can drive electric switch effectively.
In addition, preferably, be provided with a pair of polarization electrode in the groove that forms on the surface of above-mentioned ferroelectric substrate, above-mentioned electric field applying unit applies electric field at above-mentioned a pair of polarization electricity consumption interpolar.Thus, Electric Field Distribution becomes evenly, has reduced the voltage that is used for driving electric switch.In addition, the influence of surface charge diminishes, and has improved the insulating properties between pair of electrodes.
In addition, above-mentioned electric field applying unit can be the electric switch element that is made of semi-conducting material.
In addition, preferably, has the heating part of the above-mentioned ferroelectric substrate of heating.Thus, by heating ferroelectric substrate, can be with the low voltage drive electric switch.
In addition, preferably, above-mentioned ferroelectric substrate has the ilmenite structure.Thus, the resistance of ferroelectric substrate reduces and becomes big.
In addition, preferably, the movement of electric charges of the above-mentioned ferroelectric substrate when changing above-mentioned polarised direction flows through electric current between above-mentioned pair of electrodes, make the resistance change between above-mentioned pair of electrodes.Thus, because the minimum flow of charge mistake that 2Ps * S is also arranged, resistance value significantly changes more than 2 figure places, so can use as switch fully.
In addition, preferably, above-mentioned ferroelectric substrate has been implemented the direction that makes spontaneous polarization and has handled along the polarization (poling) of single direction unanimity substantially.Thus, in crystallization no strain residual, can make the polarization is directed on the direction.
In addition, preferably, between at least one and above-mentioned ferroelectric substrate of above-mentioned pair of electrodes, be provided with insulating barrier.Thus, the electric field that can reduce to apply in order to make polarization reversal can drive electric switch with low power consumption.
In addition, memory element of the present invention is to use electric switch of the present invention to constitute.Thus, can realize the nonvolatile memory of high integration with simple structure.
In addition, preferably, above-mentioned each electric switch is arranged with a plurality of two-dimensionally.Thus, can easily realize two dimensional memory.
In addition, preferably, above-mentioned each electric switch is formed with a plurality of on semiconductor integrated circuit, and above-mentioned electric field applying unit is controlled by above-mentioned semiconductor integrated circuit.Thus, can easily control each electric switch.
In addition, preferably, the resistance value of the above-mentioned ferroelectric substrate of above-mentioned each electric switch is controlled by above-mentioned semiconductor integrated circuit, and the resistance value of the above-mentioned ferroelectric substrate of above-mentioned each electric switch is detected by above-mentioned semiconductor integrated circuit.Thus, easily stored information, easily read institute's canned data.
In addition, preferably, have illumination part, above-mentioned illumination part is mapped to the illumination below the wavelength 500nm on the above-mentioned ferroelectric substrate of each electric switch.Thus,, can make the resistance high resistanceization of all electric switches, so can realize the memory element that institute's canned data can be eliminated together by to all ferroelectric substrate irradiates lights.
In addition, preferably, has heating part with the above-mentioned ferroelectric substrate heating of above-mentioned each electric switch.Thus,, can make the resistance high resistanceization of all electric switches, so can realize the memory element that institute's canned data can be eliminated together by heating all ferroelectric substrates.
Ferroelectric electric switch of the present invention and use its memory element is to have utilized the variation of the ferroelectric spontaneous polarization that ferroelectric conductivity brings along with applying electric field and the characteristic that significantly changes.Particularly, be the variation that has utilized along with spontaneous polarization, ferroelectric from insulator to semiconductor or from the phenomenon of semiconductor to its conductivity marked change of insulator.This phenomenon is unknown by the people in the past, is that present inventors find according to experimental result.Utilize the variable characteristic of this ferroelectric conductivity, can realize the memory element of electric switch and this electric switch of use.
Specify embodiments of the present invention below.
(execution mode 1)
Electric switch to embodiments of the present invention 1 is illustrated.Figure 1A is the stereogram of structure of the electric switch 10a of expression embodiments of the present invention 1.In addition, Figure 1B is the stereogram of structure of the another kind of electric switch 10b of expression embodiments of the present invention 1.Shown in Figure 1A, the electric switch 10a of execution mode 1 has: the ferroelectric substrate 1 that has added metal; Electrode pair 2; The electric field applying unit, promptly voltage source 4.Electrode pair 2 is arranged on the ferroelectric substrate.Arrow among Figure 1A is represented the polarised direction of ferroelectric substrate 1.Electrode pair 2 is connected with voltage source 4 respectively.Electrode pair 2 is arranged on the surface and the back side of ferroelectric substrate 1, and they are along the direction configuration of polarization.
Action to this electric switch 10a is illustrated.At first, electrode pair 2 is being applied under the state of electric field, ferroelectric substrate 1 is an insulator, so conductivity is lower.Be high resistance, between electrode pair 2, do not have electric current to flow through.Then, the spontaneous polarization direction by voltage source 4 and ferroelectric substrate 1 applies electric field opposed to each other.Voltage source 4 can apply electric field to ferroelectric substrate 1, and the polarised direction of the part of ferroelectric substrate 1 is changed.Spontaneous polarization is reversed fully, if polarization finishes, then the conductivity between the electrode pair 2 uprises.Be to be low resistance between the electrode pair 2, electric current flows through.Then, if apply electric field opposite with the direction of present polarization reversal towards (spontaneous polarization originally towards) with 4 pairs of ferroelectric substrates 1 of voltage source, then the polarization of ferroelectric substrate 1 is returned to original spontaneous polarization state (counter-rotating again).Under this state, become high resistance between the electrode pair 2 once more.Like this,, can make electrolysis between 2, become conducting or non-conduction, move as switch by control voltage source 4.
Figure 1B is the stereogram of structure of the electric switch of the another kind of execution mode 1 of expression.With the difference of Figure 1A be: surperficial parallel towards with respect to ferroelectric substrate 1 of the spontaneous polarization of ferroelectric substrate 1 indicated by the arrow, electrode pair 2 along spontaneous polarization towards direction arranged side by side, be arranged on the same one side of ferroelectric substrate 1.In this structure, also the part that can change ferroelectric substrate 1 by control voltage source 4 is the polarised direction between the electrode pair 2.Thus, can make electrolysis between 2, become conducting or non-conduction.
Then, illustrate that the polarised direction by control ferroelectric substrate 1 can change the reason of the conductivity of ferroelectric substrate 1.Ferroelectric characteristic at first is described.Ferroelectric material has spontaneous polarization, and its polarised direction externally changes under the effect of electric field.Fig. 2 A, Fig. 2 B and Fig. 2 C are the figure that is used for illustrating the polarised direction when the ferroelectric substrate applied voltage, and Fig. 2 D is the electric field of the hysteresis characteristic of expression when the ferroelectric substrate is applied voltage and the graph of a relation of polarization.
When applying electric field, knownly show the hysteresis characteristic shown in Fig. 2 D by 4 pairs of ferroelectric substrates 1 of voltage source.Ferroelectric substrate 1 has the biasing of electric charge in crystallization, inside has electric field.This is called spontaneous polarization (Ps).If applying voltage from the outside with the opposed direction of this electric field, then the direction of spontaneous polarization changes.
For example, have in the single shaft direction under the situation of polarization, polarised direction has only 2 kinds.Shown in Fig. 2 A～Fig. 2 C, it is opposed that electrode pair 2 is set to clip ferroelectric substrate 1, is configured such that also electrode pair 2 opposed directions are along polarised direction.In addition, the arrow among the figure is represented the direction that polarizes.At first, ferroelectric substrate 1 is not being applied under the state of electric field, 1 spontaneous polarization of ferroelectric substrate, polarised direction is upwards in Fig. 2 A.If applying electric field with the opposed direction of polarised direction (downward among Fig. 2 A) by 4 pairs of these ferroelectric substrates 1 of voltage source, the moment that then surpasses counter-rotating electric field-Ec at the electric field that applies, the part of ferroelectric substrate 1 be the polarised direction of the periphery of electrode pair 2 do 180 degree counter-rotatings (Ps becomes-Ps), become the state shown in Fig. 2 B.In addition, in Fig. 2 A～Fig. 2 C, will make progress as "+" direction, will be downwards as "-" direction.As such to the state shown in Fig. 2 B from the state variation shown in Fig. 2 A, polarised direction is changed to reciprocal phenomenon and is called polarization reversal.As can be known, the state of Fig. 2 A is the place shown in the state 32a in Fig. 2 D, is applying electric field and becomes-during Ec, be changed to the state shown in the state 32b.The state that state 32c is arranged between state 32a and state 32b in addition.In addition, if by voltage source 4 from the outside in the opposite direction (the last direction Fig. 2 B) of polarization to ferroelectric substrate 1 (Fig. 2 B) on-load voltage of state 32b, then surpass the moment of Ec at electric field, polarised direction becomes and makes progress like that shown in Fig. 2 A.That is, in Fig. 2 D, be changed to state 32a via state 32d from state 32b.
Under the state 32a in Fig. 2 D, ferroelectric substrate 1 is original crystalline state, and under state 32b, the spontaneous polarization of the ferroelectric substrate 1 between the electrode pair 2 is an inverted status.State 32a and state 32b are stable states, and state 32c and state 32d are to the intermediateness of state 32a and state 32b variation, can regard crystal structure unsure state, transition state as.That is, shown in Fig. 2 C, only a part of reverse-poled of electrode pair 2 peripheries is not electrode pair 2 peripheral perfact polarization counter-rotatings.Therefore, at electrode 2 peripheries, polarised direction is that the downward polarization of reverse-poled mixes the state that exists with the upwards polarization of spontaneous polarization.In addition, spontaneous polarization is polarized to internal electric field.
Then, the electric current of the state that above-mentioned such polarised direction is changed changes and is illustrated.Ferroelectric is generally insulator, near the counter-rotating electric field Ec that polarization reversal takes place, has immediate current to flow through by the moving of internal charge that is accompanied by the spontaneous polarization counter-rotating.The quantity of electric charge of this electric current is proportional with counter-rotating area S, represents with 2Ps * S.If polarization reversal finishes, flow through this quantity of electric charge 2Ps * S that reverses required, then the mobile of electric current stops, and ferroelectric reverts to insulator.That is, only have electric current to flow through in the moment that polarization reversal takes place, this magnitude of current is also little.For example, utilize the electric current that transient flow is crossed between electrode pair 2 by this movement of electric charges, can carry out switch.
In addition, when insulator is applied high voltage, can produce the phenomenon of the so-called insulation damages that the electrical conductivity of insulator increases.This is that crystal structure is damaged by high electric field and loses the phenomenon of insulating properties, owing to crystallization is damaged crystal structure itself is changed, and is irreversible phenomenon.
Present inventors find that in ferroelectric crystallization, except insulation damages, electrical conductivity can increase in ferroelectric material.And then it can reversibly increase electrical conductivity.Particularly, in the uniaxiality ferroelectric substrate 1 with Fig. 2 A～Fig. 2 D explanation, state 32a among Fig. 2 D and 32b are stable status as mentioned above, and state 32c and 32d are transition state.But state 32c and 32d exist as the crystalline state of ferroelectric substrate 1, like this, under the state of a part of polarization reversal of the crystallization of ferroelectric substrate 1, find that the resistance of the crystallization of ferroelectric substrate 1 significantly reduces.The low resistance state of this ferroelectric substrate 1 is to exist among state 32c and the state 32d in the interstage to state 32a and 32b variation only.State 32c is a state such shown in Fig. 2 C, like this, is taking place on the part between the electrode pair 2 under the state of polarization reversal, and the resistance of ferroelectric substrate 1 reduces.
At first, if ferroelectric substrate 1 is applied and the opposed electric field of the spontaneous polarization of ferroelectric substrate 1 (about 2.6kV/mm), this ferroelectric substrate 1 is the Mg Li doped NbO to the Z plate 3Crystallization is carried out single polarization and is handled and obtain, and then in the moment of the polarization reversal of the part of crystallization, the resistance that observes crystallization significantly reduces.This ferroelectric substrate 1 is a resistance 10 10If the insulator that Ω cm is above is beginning polarization reversal then be reduced to 10 6Below the Ω cm.If continue to apply voltage again, then polarization reversal is proceeded, if polarization is reversed fully then reverted to insulator.Like this, as Mg Li doped NbO 3The ferroelectric substrate 1 of crystallization significantly reduce at the resistance of the stage crystallization midway of polarization reversal.In addition, if about 200 ℃ ferroelectric substrate 1 is being heat-treated under the state of low resistanceization, then by high resistanceization, resistance reaches the value that approaches original state.This moment polarization inversion unit shape invarianceization.
In addition, in the another kind experiment, to Mg Li doped NbO with the Z plate 3Crystallization (incorporation of Mg is 5mol%) is carried out single polarization and is handled the ferroelectric substrate 1 that constitutes, and applies and the opposed electric field of its spontaneous polarization (about 4kV/mm).As a result, in the moment of a part of polarization reversal of crystallization, the resistance of ferroelectric substrate 1 significantly reduces.Originally resistance is the above insulator of 1G Ω cm, if the beginning polarization reversal then is reduced to below the 1MG Ω cm.If continue to apply electric field again, then resistance increases once more.
Can expect by these results, at Mg Li doped NbO 3The interpolation that crystallization is such in the ferroelectric substrate of metal, after just beginning to form polarization reversal, under the residual state that internal electric field arranged, ferroelectric resistance can reduce.In addition, so-called internal electric field is meant after just beginning to make the spontaneous polarization counter-rotating, with the opposed electric field of the polarization that remains in the counter-rotating in the crystallization inside.
Like this, the phenomenon that reduces at the resistance midway of polarization reversal is at LiNbO 3, LiTaO 3And can observe in the ferroelectric crystallization such as KTP.Under the state that resistance reduces, in the inner strain that has the crystal structure that produces because of polarization reversal of crystallization, residual have and the opposed electric field of reverse-poled.Under this state, if apply and reverse after the opposed electric field of polarization, counter-rotating more then takes place under than the low voltage of common counter-rotating electric field Ec, turn back to original spontaneous polarization state.
State current-voltage characteristic separately shown in state shown in Fig. 3 presentation graphs 2A and Fig. 2 C.In Fig. 3, what solid line was represented is the state shown in Fig. 2 A, and what dotted line was represented is the state shown in Fig. 2 C.As shown in Figure 3, under the state of such ferroelectric substrate 1 perfact polarization shown in Fig. 2 A, ferroelectric substrate 1 is an insulator, does not have electric current to flow through.But, shown in Fig. 2 C, proceed to state midway and exist under the state with the opposed internal electric field of spontaneous polarization that reverses, ferroelectric substrate 1 low resistanceization and have electric current to flow through in polarization reversal.That is,, can see that ferroelectric resistance significantly reduces being in the state that being reversed between electrode of polarization take place fully and existing under the situation about not setting up simultaneously with these 2 conditions of the opposed internal electric field of spontaneous polarization of reversing.
Shown in Fig. 2 A or Fig. 2 B, if polarization reversal is carried out between electrode fully, then resistance becomes big once more.As the polarization reversal part, be preferably interelectrode about 10%～90%.In addition, it also is very important having internal electrode.As mentioned above, if the ferroelectric of low resistanceization is heat-treated then the resistance rising, can think that this is because the cause that internal electric field reduces about 200 ℃.In addition, the reduction of resistance can be thought because the strain of the crystal structure that produces by polarization reversal takes place.The strain of crystallization is the major reason of internal electric field, is because there is the reduction that resistance has taken place under the situation of internal electric field.
In addition, the ferroelectric resistance value of the state of resistance low resistanceization also is the degree same with semiconductor, and its characteristic also demonstrates the characteristic same with semiconductor.Particularly, ferroelectric has rectification characteristic.For example, deposit film on ferroelectric is investigated its current-voltage characteristic, and the result is because of the kind characteristic marked change of metal film.Can think that this is that rectification characteristic because of the working function of metal film variation has taken place because variation has taken place the state of the Schottky barrier of the contact portion between metal-semiconductor.That is, the ferroelectric of low resistanceization shows semi-conductive characteristic by part polarization.
As mentioned above, at the Mg of X plate Li doped NbO 3In, polarization inversion unit shows rectification characteristic, low resistanceization, and this sets forth.But this is a polarization reversal part low resistanceization, and is such with the ferroelectric substrate 1 of present embodiment 1, because of polarization reversal is different with existence low resistanceization along with the internal electric field of polarization reversal.
As mentioned above, the electric switch of execution mode 1 has: the state that internal electric field and polarization opposed with it all exist in ferroelectric substrate 1 (with reference to Fig. 2 C), state (with reference to Fig. 2 A or Fig. 2 B) with ferroelectric substrate 1 perfact polarization, by switching to wherein any state, with ferroelectric substrate 1 difference low resistanceization or high resistanceization.Thus, controlling electric switch is conducting or non-conduction.
But the state that has internal electric field is that crystal structure is unsettled.So, time of the resistance of the ferroelectric substrate 1 of low resistanceization changed measures.Time and changes in resistance when Fig. 4 A is illustrated in ferroelectric substrate 1 applied direct voltage.Make ferroelectric substrate 1 become the state shown in Fig. 2 C, the temperature survey of ferroelectric substrate 1 is 120 ℃.Shown in Fig. 4 A, resistance value increases gradually along with the process of time, becomes 2～3 times in several hours.This resistance that demonstrates the polarization reversal part increased along with the time.Changes in resistance is relevant with temperature, and is at room temperature very little, if surpass 100 ℃ then became 2～3 times in several hours.To make changes in resistance not too large in order stably using, to be preferably in the temperature below 50 ℃ and to use ferroelectric substrate 1.And then, also the frequency dependence of resistance is measured.Fig. 4 B represents the frequency and the changes in resistance of ferroelectric substrate 1.Ferroelectric polarization inversion unit given add high-frequency, come measuring resistance by current-voltage characteristic.Under the situation of direct current, the resistance about 1M Ω is to be increased to about 3M Ω under the 1kHz in frequency.But, change if observe the time of resistance, then make timeliness change almost disappearance by increasing frequency as can be known.In Fig. 4 B, also represent the resistance variable quantity of process in time.Shown in Fig. 4 B, under direct voltage or the situation less than the interchange of 5Hz, resistance value increased along with the time.But, for the interchange more than the 10Hz, almost there is not the time of resistance value to change, demonstrate stable value.Thus, as the signal of switch of control electric switch, use more than or equal to the AC signal of 5Hz just can, more preferably use the AC signal more than the 10Hz.
As mentioned above, make under the situation of ferroelectric substrate 1 low resistanceization its resistance relevant with the frequency of the high-frequency electric field that is applied (with reference to Fig. 4 B) by polarization reversal.Particularly, resistance increases if frequency becomes greatly.In addition, in that the ferroelectric substrate 1 of low resistanceization reverses again in order to make, high resistanceization and when applying electric field, must make the high-current flow mistake.So, as long as it is just passable to apply the high-frequency electric field that superposeed.Thus, the high resistanceization of ferroelectric substrate 1 can be realized, the electric current when applying electric field can be reduced.Therefore, can reduce the driving electric of electric switch.
Resistance value during with the ferroelectric low resistance is relevant with the surface area that polarization reversal takes place.Fig. 5 A is the vertical view of electrode that is used for illustrating the shape of electrode.Shown in Fig. 2 A, electrode pair 2 is being arranged setting on the polarised direction of ferroelectric substrate 1.Shown in Fig. 5 A, be preferably the shape of electrode pair 2 is made comb poles.Thus, can make the length of periphery of electrode pair 2 elongated.Fig. 5 B represents the length of periphery of each electrode of electrode pair 2 and the relation of resistance.Shown in Fig. 5 B, the length of the periphery (electrode edge) of each electrode by making electrode pair 2 is elongated, can make the resistance of ferroelectric substrate 1 become lower.That is, even identical electrode area, the electrode shape of making long peripheral distance can become lower resistance.So, can use for example comb poles etc.
In addition, also can use and for example have the dendritic electrode that electrode refers to and come shape electrode 2 on both sides.As the direction of electrode, if to make the direction of the finger of comb shape be the Y direction of crystallization then can improve characteristic.At the Mg Li doped NbO that uses the Z plate 3In the experiment of substrate, the easy degree that forms polarization reversal as can be known is different because of the direction that comb shape refers to.The direction situation consistent with Y direction that comb shape is referred to compared with the situation on the X-direction that is formed on its 90 ° of quadratures, and the diffusion velocity of polarization reversal is more than 10 times.Therefore, the direction that is formed at the finger of the comb shape in the crystallization preferably is set at Y direction.
In addition, as ferroelectric substrate 1, used the LiNbO of the Mg that mixed 3, this is because at LiNbO 3Can not get same effect in the crystallization.At LiNbO 3In itself, can't see the significantly raising that electrical conductivity is followed polarization reversal, in the characteristic of insulator, do not change.That is,, can realize that electrical conductivity changes along with the variation of polarised direction by in ferroelectric, adding metal.Equally, for LiTaO 3, at LiTaO 3In the crystalline monomer, before and after polarization reversal the variation of electrical conductivity not taking place, and be insulator equally, by metallic additionses such as interpolation Mg, can observe the variation of electrical conductivity.At the incorporation of the Mg that adds during, follow the changes in resistance amount of the ferroelectric substrate 1 that above-mentioned polarised direction changes to reduce about several percentage points significantly less than 1mol%.In order to realize the bigger resistance variations more than 10%, need to add the above metal of 1mol%.If it is carry out the above interpolation of 3mol% then resistance becomes below 1/10, just more effective.In addition, in other ferroelectric material,, can both realize the variation of same electrical conductivity so long as can increase the metal incorporation.
In addition, as ferroelectric substrate 1, also can be that the material of crystal grain such as imperfect crystal formation, crystallite just can access same effect so long as for example exist beyond the ferroelectric crystallization of single polarization.If utilize amorphous, crystallite structure, can utilize thin-film material, so do not need a large amount of crystalline growths, device manufacturing becomes easy.In addition,, crystallite amorphous by making can increase the incorporation of metallic additions.So can increase the changes in resistance amount of 2 of electrode pairs.But, if owing to increase the incorporation of metal then the lattice strain of crystallization increases, so when drawing large-scale crystallization, can produce crack etc., the growth of the uniform large-scale crystallization difficulty that becomes.For example at LiNbO 3Situation under be difficult to add the above Mg of 10mol%, so under the situation of using single crystallization base plate, incorporation is preferably below the 10mol%.
In addition, make the MgO:LiNbO of the single polarization of spontaneous polarization 3, but for the ferroelectric that has added other metals, for example added the LiNbO of metals such as In, Sc, Cu and Fe 3, LiTaO 3, KTP or their crystallization mixed crystallization, also can access same effect.
In addition, material as ferroelectric substrate 1, the direction that also can be spontaneous polarization is perpendicular to the material beyond the Z base board on surface, for example also can be spontaneous polarization direction X plate parallel with base plan or Y plate or with cutting of substrate surface skewed crossing surplus (off-cut) substrate etc.It is controlled higher owing to what polarize to cut the complementary basis plate, uniform polarization reversal reproducibility is formed well, so more preferably.
In addition, as mentioned above, near room temperature, ferroelectric resistance variations is observed.Observe ferroelectric significantly resistance and reduce, might more cause the superconduction effect under the low temperature.Crystallization instability as described above under the higher state of temperature, the restriction of intersexuality sometimes by using at low temperatures, can solve the unsteadiness of crystallization.If under the low temperature below 0 ℃, utilize ferroelectric then can demonstrate superconducting characteristic, and by utilizing polarization reversal can constitute the electric switch of superconduction, so be effective.
(execution mode 2)
Use accompanying drawing that the electric switch of embodiments of the present invention 2 is illustrated.The electric switch of execution mode 2 and execution mode 1 are same, be by the polarization that the ferroelectric substrate of metal has been added in control change the ferroelectric substrate resistance, make the ferroelectric substrate become conducting or non-conduction electric switch.Though the structures of the configuration of electrode and electric field applying unit etc. are different, with employed ferroelectric substrate make with execution mode 1 in use identical just passable.
Fig. 6 A and Fig. 6 B are the figure of structure of the electric switch of expression execution mode 2.Fig. 6 A is the end view of structure of the 1st electric switch of expression execution mode 2.In the drawings, voltage is set to electrode pair 52, they are arranged along the direction of the spontaneous polarization of the ferroelectric substrate 51 shown in the arrow.In addition, voltage with electrode pair 52 clip ferroelectric substrate 51 ground be arranged on its surface and the back side on.And then, be provided with voltage with a face in the face of electrode pair 52 on, be provided with electric current with electrode pair 53 along the vertical direction of polarised direction.In addition, Fig. 6 B is the vertical view of structure of the electric switch of expression execution mode 2.A face of ferroelectric substrate 56 is provided with voltage with electrode pair 57, and they are arranged along the direction of the spontaneous polarization shown in the arrow.And then, be provided with voltage with same of the face of electrode pair 57 on, be provided with electric current with electrode 58 along the vertical direction of polarised direction.In Fig. 6 A and Fig. 6 B, voltage source 54 is electrically connected with electrode pair 52 and 57 with voltage, and current source 55 is electrically connected with electrode pair 53 and 58 with electric current.In addition, the ferroelectric substrate 51 of Fig. 6 A is the Z plate, and the ferroelectric substrate 56 of Fig. 6 B can be X plate or Y plate.In addition, in Fig. 6 A and Fig. 6 B, also can use and cut the complementary basis plate.
In the electric switch shown in Fig. 6 A and Fig. 6 B, working voltage source 54, at voltage with 52 of electrode pairs or voltage with 57 of electrode pairs, apply selectively with the electric field of the opposed direction of spontaneous polarization of ferroelectric substrate 51 and ferroelectric substrate 56 or with the unidirectional electric field of spontaneous polarization.Thus, voltage can be controlled to be high resistance or low resistance with 52 of electrode pairs and voltage respectively with the resistance of 57 of electrode pairs.By doing like this, also with 58 of electrode pairs resistance is controlled to be low resistance or high resistance with 53 of electrode pairs and electric current at electric current, electric current becomes conducting or non-conduction.
Fig. 7 A is the end view of structure of the 3rd electric switch of expression execution mode 2.The electric switch of Fig. 7 A is the electric switch that the current value of 62 of electrode pairs is carried out switch.Be formed with electrode (electrode pair 62) along polarised direction on the surface of ferroelectric substrate 61 and the back side, this electrode pair 62 is electrically connected with voltage source 63.
The electric field that is applied to 62 of electrode pairs by voltage source 63 is for surpassing the impulse electric field of counter-rotating electric field Ec.By applying electric field, a part of polarization reversal that the electrode pair on the ferroelectric substrate 61 is 62, the resistance reduction of ferroelectric substrate 61.Fig. 7 B is the figure that is illustrated in 62 electric currents that flow through of electrode pair and time relation.In Fig. 7 B, the place 64 of current-jump is the moment that applies impulse electric field.If apply impulse electric field, then the resistance of ferroelectric substrate 61 reduces, and shown in Fig. 7 B, flows through electric current 62 of electrode pairs.And then if apply the pulse voltage of "-", then electric current does not flow.That is, the place 65 of the current-jump of Fig. 7 B is the moment that has applied "-" pulse voltage.Like this,, the value of mobile electric current can be changed, switch can be carried out by superimposed pulse voltage in electric current.
Fig. 8 A is the end view of structure of the 4th electric switch of expression execution mode 2.The polarised direction of this electric switch (representing with arrow among the figure) differs 180 degree with the electric switch of Fig. 7 A, and other structures are identical.Voltage source 63 can make the pulse voltage that is applied on the ferroelectric substrate 61 alternately be "+" or "-".The figure of the relation of Fig. 8 B voltage that to be expression apply the ferroelectric substrate of the 4th electric switch of present embodiment 2 and effluxion.In addition, Fig. 8 C is the figure that is illustrated in the relation of the electric current that flows through in the 4th electric switch of present embodiment 2 and effluxion.By such pulse voltage shown in Fig. 8 B is applied to 62 of electrode pairs, can access current waveform such shown in Fig. 8 C.Hence one can see that, and the 4th electric switch moves as rectifier cell.That is, if the pulse voltage of voltage source 63 is applied in "-", then produce polarization reversal, electric current flows through, the then polarization reversal disappearance of voltage, the electric current that apply "+" do not flow through.By repeating this action, just can access rectification characteristic.Must apply counter-rotating electric field Ec (2.6Kv/mm) in order to carry out polarization reversal, but, use the following electric field of 0.5Kv/mm also to be fine in order to make the polarization reversal part reverse again and restore to the original state.This is because by existing internal electric field that reversal voltage is reduced.
(execution mode 3)
Use accompanying drawing that the electric switch of embodiments of the present invention 3 is illustrated.
In ferroelectric material, the state that being accompanied by the counter-rotating, electrical conductivity of spontaneous polarization increases reversibly exists, and is illustrated in execution mode 1 for this phenomenon, has set forth the opinion whether this phenomenon is subjected to the influence of builtin voltage.But,, except above-mentioned, can also enumerate the existence that has or not domain wall as the reason that produces this phenomenon.As domain wall, be do not exist together each other boundary line of polarised direction.Ferroelectric resistance is because of having or not the domain wall marked change.There is domain wall in initial stage the ferroelectric substrate being applied electric field between electrode, consider whether resistance therefore and significantly reduces.And then, if continue to apply electric field then polarization-reversed region expansion, if the polarization reversal end then forms the big polarization-reversed region of specific electrode surface.Because domain wall away from electrode, can increase once more so can expect interelectrode resistance.
Can think that there is bigger strain in crystal structure, has bigger internal electric field in the zone of spontaneous polarization acute variation in domain wall, be the reason that causes this phenomenon.So, in execution mode 3, also add the explanation of domain wall, electric switch is illustrated.
Fig. 9 A～Fig. 9 D is the figure of structure of the electric switch of expression embodiments of the present invention 3.Fig. 9 A is the vertical view of the structure of expression electric switch, Fig. 9 B is the cutaway view of the structure of expression electric switch, Fig. 9 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Fig. 9 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.In Fig. 9 A～Fig. 9 D, on the surface of ferroelectric substrate 81, be formed with electrode pair 82.This ferroelectric substrate 81 use by the ferroelectric substrate of execution mode 1 and execution mode 2 explanations just can, have same effect.The spontaneous polarization direction of ferroelectric substrate 81 is represented with arrow in the drawings.Along the spontaneous polarization direction, this electrode pair 82 is arranged along the spontaneous polarization direction of ferroelectric substrate 81 and is provided with.Shown in Fig. 9 A and Fig. 9 B, under the state that spontaneous polarization is changed, do not form the different zone of polarization 82 of electrode pairs, do not form domain wall.Under this state, ferroelectric substrate 81 is a high resistance, and wanting to flow through electric current 82 of electrode pairs can not.By the electric field applying unit that spontaneous polarization is changed, change the spontaneous polarization direction of ferroelectric substrate 81, thereby shown in Fig. 9 C and Fig. 9 D, produce the different zone 83 of polarised direction 82 of electrode pairs.In zone 83 and outside the zone 83, the polarised direction difference.The boundary line that this polarised direction is different is a domain wall 84.Because resistance significantly reduces in domain wall 84, so 82 low resistanceizations of electrode pair.Therefore, there is electric current to flow through 82 of electrode pairs.
In addition, though diagram not, shown in enforcement mode 1 and 2, the electric field applying unit is so long as can to apply for example voltage source etc. of electric field in the other direction at spontaneous polarization direction or its just passable.In addition, also can be at 82 voltage sources that apply voltage of electrode pair.As mentioned above,, apply voltage, can produce domain wall 84, thus, can change the resistance of 82 of electrode pairs in spontaneous polarization direction and opposite direction by 82 of electrode pairs.
The polarised direction in the zone 83 that polarised direction is different is different because of the difference of ferroelectric substrate 81.For example, at the MgO:LiNbO that uses single polarization 3Under the situation as ferroelectric substrate 81, make polarised direction change 180 ° by polarization reversal.Therefore, in the zone 83 different with ferroelectric substrate 81 polarised directions, polarised direction differs 180 °.Except this polarised direction, also has the surperficial parallel situation of polarised direction and ferroelectric substrate 81, perpendicular to the situation on ferroelectric substrate 81 surfaces and with respect to the situation of ferroelectric substrate 81 surface tilt etc.In addition, also have the stabilising direction of polarization to have a plurality of situations, in this case, determine the direction of polarization by the direction of an electric field that applies.
Ferroelectric substrate 81 is the crystallization of single polarization, and does not have in polarised direction under the situation of single polarization, the 81 single polarization of ferroelectric substrate need be handled the back and use.In addition, the thin film crystallization etc. that can use materials such as crystallite, amorphous, pottery, monocrystalline, liquid layer growth is as ferroelectric substrate 81, but because their polarised direction exists pell-mell, implements polarization and handle so be preferably.Handle as polarization, be meant that temperature increase with each material near the Curie temperature of its crystallization, by applying electric field, makes the processing method of polarised direction unanimity.Form spontaneous polarization owing to improve temperature, so in domain wall 84, be difficult for residual crystal strain.By cooling gradually under this state, can form the ferroelectric substrate 81 of microcosmic polarised direction unanimity.
For the low resistance state of the ferroelectric substrate 81 after handling of realizing polarizing, being preferably and making the temperature of ferroelectric substrate 81 is the temperature more much lower than Curie temperature, applies and the opposed electric field of poling electric field.Curie temperature mostly is hundreds of ℃ greatly.Therefore, polarization reversal temperature is preferably below 1/2 or below 100 ℃ of Curie temperature.By doing like this, can do origin cause of formation polarization reversal and make the state of residual crystal strain on the domain wall.
In Fig. 9 A～Fig. 9 D, use Mg Li doped NbO has been described 3Situation as ferroelectric substrate 81.The incorporation of Mg is 5mol%, is the crystallization after the single polarization of X cutting substrate is handled, and has the direction of spontaneous polarization, the direction that it is arranged along this electrode pair 82.Under the state of Fig. 9 A and Fig. 9 B, at 82 electric fields that apply 5kV/mm of electrode pair, be the opposite direction of spontaneous polarization by not shown electric field applying unit.For example, if make electrode pair 82 each other be spaced apart 1 μ m, then applying voltage is 5V.Produce domain wall by applying voltage.Promptly be changed to the state of Fig. 9 C and Fig. 9 D.This moment, the resistance of 82 of electrode pairs was hundreds of Ω.
If then applying for example voltage of 5V with opposite just now direction, then return to the state of Fig. 9 A and Fig. 9 B once more, the resistance that electrode pair is 82 increases to tens k Ω.Like this, the changes in resistance rate is more than 2 figure places.Promptly more than 100 times.
In addition, carry out applying the operation of above-mentioned electric field repeatedly, but can change the resistance of 82 of electrode pairs equally.After this resistance value of each state of Fig. 9 A, Fig. 9 B, Fig. 9 C and Fig. 9 D is exactly stable just changing a little after changing, even also can not change through some months resistance like this.Like this, because the polarization of ferroelectric substrate 81 is highly stable, so need not accept the electric supply from the outside halfway, the electric switch of execution mode 3 is the maintained switch state for good and all.
When changing the polarised direction of ferroelectric substrate 81, form or eliminated domain wall 84, but have bigger crystal strain at the position that produces domain wall 84 thus.Therefore, when increasing number of repetition, can residual crystallinity damage, but the crystallinity damage is relevant with the size in the zone of domain wall 84 the proportional minimizing of the boundary of action frequency and area.Area at domain wall is 1mm 2Under the above situation, number of repetition is about 1000 times.In order to realize the switch number of times more than 100,000 times, need only the domain wall area constraints at 100 μ m 2Below just can.By further area being reduced to 10 μ m 2Below, can further increase number of repetition.
In ferroelectric substrate 81, be doped with Mg as mentioned above.Add metallic additions like this owing to can reduce to be used for to make the value of the counter-rotating electric field Ec of spontaneous polarization counter-rotating, so be effective.For example, at LiNbO 3Under the situation of monomer crystallization, the value of counter-rotating electric field Ec is about 20Kv/mm, and by the magnesium about doping 5mol%, counter-rotating electric field Ec can be reduced to about 1/4.If crystallization applied voltage then make crystal strain, if apply high voltage repeatedly then can produce crack etc. by electrostriction effect.Therefore, it is more little to apply voltage to ferroelectric substrate 81, and the life-span of electric switch is long more.Add by carrying out metal, can significantly reduce applying voltage, thus the increase of the switch number of repetition of electric switch, so be effective.
In addition, value and the crystal structure of counter-rotating electric field Ec have much relations.Become effectively because crystallization is drawn, the suitable composition of ratio of components (congruent composition) is drawn so the crystallization of ferroelectric substrate 81 is mostly to depart from completely slightly.This is because the uniform crystallization of the easier drawing of this composition.Relative therewith, form (stoichiometric composition) by making it become chemical dose as can be known, the value of counter-rotating electric field Ec can significantly reduce.This is because the defect concentration that chemical dose is formed in the crystallization is littler, the control easily so spontaneous polarization becomes.For example at LiNbO 3, LiTaO 3In, the value of counter-rotating electric field Ec is reduced near 1/10 from 1/4.So, by using the chemical dose crystallization, can realize applying the lower voltage of voltage as ferroelectric substrate 81, can significantly increase the life-span of electric switch.In addition, the crystallization that chemical dose is formed, except crystallization draws, the also film forming that can be undertaken by epitaxial growth and easily forming.By using the ferroelectric substrate 81 of epitaxial film, can easily reduce counter-rotating electric field Ec, can increase the switch life of electric switch.
In addition, in execution mode 3, on the surface of ferroelectric substrate 81, form electrode pair 82, but the configuration of electrode pair 82 is not limited to this.For example, also can access same effect by ferroelectric substrate 81 being made filming, on its surface and the back side, being formed.In addition, what the resistance of ferroelectric substrate 81 reduced is the part of domain wall, so can reduce resistance by increasing the domain wall area.For example, the area of domain wall can be increased, ferroelectric substrate 81 low resistanceizations can be further made by electrode pair 82 is made comb poles etc.
Figure 10 is the structure chart of structure of the another kind of electric switch of expression execution mode 3.Ferroelectric substrate 91 is identical with above-mentioned ferroelectric substrate.Being formed with groove on the surface of ferroelectric substrate 91 is groove 96, and electrode pair 92 is formed at wherein.And then ferroelectric substrate 91 is provided with the heater 97 as the heating part.On electrode pair 92, connecting voltage source 98 as the electric field applying unit.In addition, the direction of plan naturally of ferroelectric substrate 91 is represented with arrow in Figure 10.The action of this electric switch is identical with above-mentioned electric switch.
In electric switch shown in Figure 10, when applying electric field, be preferably the temperature of ferroelectric substrate 91 is risen slightly than room temperature by 92 of 98 pairs of electrode pairs of voltage source.By the temperature of ferroelectric substrate 91 being become about 80 ℃, the required electric field Ec that applies of polarization reversal is reduced to about half by the heater 97 that is arranged on the ferroelectric substrate 91.Apply electric field Ec by reduction, can drive electric switch with lower consumption electric power.And then, because the strain of the crystallization that takes place when polarization reversal reduces, thus the durability of number of repetition significantly rise, so be effective.Particularly, be preferably at use ferroelectric substrate 91 more than 20 ℃.More preferably more than 40 ℃.
In addition,, Electric Field Distribution is become evenly, reduce the voltage that is used for forming the different zone of polarization by in groove 96, forming electrode pair 92.In addition, the influence of surface charge diminishes, and the insulating properties that electrode pair is 92 uprises, so be preferred.In addition, also can form electrode pair 92 in groove 96 and on the surface of ferroelectric substrate 91.
In the ferroelectric substrate 81 and 91 of execution mode 3, also can make amorphous or the crystallite structure, at this moment, can increase the incorporation of metal.In addition, by using the pottery behind the crystallite sintering etc., can utilize same characteristic.But, in film, need the boundary line of reverse-poled in order to form domain wall 84.Therefore, film need be made the to a certain degree crystal grain of above size, and as crystallite, the size that is preferably crystal grain is more than 1 μ m.The thickness of film is preferably more than the 1 μ m, below the 100 μ m.If, then can need film formation time with above-mentioned to compare film blocked up, the production variation, and can because of be used for the stress etc. of film forming substrate and produce problems such as crack.
(execution mode 4)
Use accompanying drawing that the electric switch of embodiments of the present invention 4 is illustrated.The electric switch of execution mode 4 is the structures that also have the electrode that is used for forming and eliminate domain wall in the electric switch of execution mode 3.In addition, in all figure, give identical symbol and omit explanation for parts with same function.Shown in Fig. 9 A～Fig. 9 D, make the electric switch action to having or not domain wall by control electrode.Can control ferroelectric spontaneous polarization by applying electric field.
Figure 11 A～Figure 11 D is the figure of structure of the 1st electric switch of expression embodiments of the present invention 4.Figure 11 A is the vertical view of the structure of expression electric switch, Figure 11 B is the cutaway view of the structure of expression electric switch, Figure 11 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 11 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.The 1st electric switch is formed with electrode pair 82 on the surface of ferroelectric substrate 81, and is provided with polarization electrode 95.As ferroelectric substrate 81 as long as use ferroelectric substrate just passable with characteristic of explanation among the embodiment 1～3.In addition, the spontaneous polarization direction of ferroelectric substrate 81 is represented with arrow in the drawings.Electrode pair 82 is in the same one side of ferroelectric substrate 81, along the vertical direction of the spontaneous polarization direction of ferroelectric substrate 81 and arrange setting.Polarization is provided with the direction parallel with the direction that electrode pair 82 is arranged with electrode 95 as length direction.In this electric switch,, shown in Figure 11 C and Figure 11 D, form the different zone 93 of polarization by applying electric field at electrode pair 82 and between polarizing with electrode 95.In addition, each electrode pair 82 is idiostatic each other.Periphery in the different zone 93 of polarization forms domain wall 94.Thus, 82 of electrode pairs are by low resistanceization.Under the state shown in Figure 11 A and Figure 11 B, because 82 of electrode pairs are high resistance, so do not have electric current to flow through (non-conduction) 82 of electrode pairs.But,, can make electric current flow through (conducting) 82 of electrode pairs by making the state of Figure 11 C and Figure 11 D.Promptly play effect as switch.State from Figure 11 C and Figure 11 D, by again when electrode pair 82 applies between with electrode 95 with polarization and makes 82 low resistances of electrode pair opposite direction apply voltage, 93 disappearances of different zones polarize, domain wall 94 disappears, so that the resistance high resistanceization of 82 of electrode pairs returns to original state.
Other appliance switch below is described, operating principle is same as described above, makes low resistanceization between electrode pair (conducting) by forming domain wall, and domain wall disappears and makes high resistanceization between electrode pair (non-conduction).Figure 12 A～Figure 12 D is the figure of structure of the 2nd electric switch of expression embodiments of the present invention 4.Figure 12 A is the vertical view of the structure of expression electric switch, Figure 12 B is the cutaway view of the structure of expression electric switch, Figure 12 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 12 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.The 2nd electric switch is formed with electrode pair 82 on the surface of ferroelectric substrate 81, and is provided with polarization electrode pair 105.In addition, the spontaneous polarization direction of ferroelectric substrate 81 is represented with arrow in the drawings.Electrode pair 82 is in the same one side of ferroelectric substrate 81, along the vertical direction of the spontaneous polarization direction of ferroelectric substrate 81 and arrange setting.Polarization is provided with the direction parallel with the direction that electrode pair 82 is arranged with electrode pair 105 as length direction, polarization clips electrode pair 82 each other with electrode pair 105 and is provided with.That is electrode pair 82 direction of arranging and the direction quadrature that polarizes and arrange, with electrode pair 105.In this electric switch,, shown in Figure 12 C and Figure 12 D, form the different zone 103 of polarization by between polarization is with electrode pair 105, applying electric field.Periphery in the different zone 103 of polarization forms domain wall 104.Thus, electrode pair 82 is each other by low resistanceization.Under the state shown in Figure 12 A and Figure 12 B, because 82 of electrode pairs are high resistance, so, can play effect as switch by switching these states selectively.At this moment, be preferably the direction of the spontaneous polarization that makes ferroelectric substrate 81 and be formed on the direction almost parallel of polarization with the electric field between the electrode pair 105.Thus, can reduce to be used for to control the electric field of the spontaneous polarization direction of ferroelectric substrate 81.
When the state shown in Figure 12 A and Figure 12 B begins to change to state shown in Figure 12 C and Figure 12 D, polarization is applied electric field with 105 of electrode pairs, but owing to do not have domain wall 104 at this moment, so ferroelectric substrate 81 is a high resistance state, it is easy applying electric field.But, when the state that begins to change to from the state shown in Figure 12 C and Figure 12 D shown in Figure 12 A and Figure 12 B, owing to have domain wall 104 with 105 of electrode pairs in polarization, so the resistance step-down, because electric current flows easily, so the electric power that consumes when applying electric field becomes greatly.In order to prevent this situation, for example forming between polarization is with electrode pair 105 and ferroelectric substrate 81, insulator film is effective.For example pass through SiO 2Be deposited in polarization with between electrode pair 105 and the ferroelectric substrate 81 Deng insulator film, can prevent flowing of electric current, the power consumption in the time of can significantly reducing the control polarization.
Figure 13 A～Figure 13 D is the figure of structure of the 3rd electric switch of expression embodiments of the present invention 4.Figure 13 A is the vertical view of the structure of expression electric switch, Figure 13 B is the cutaway view of the structure of expression electric switch, Figure 13 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 13 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.The 3rd electric switch is formed with electrode pair 82 on the surface of ferroelectric substrate 81, and is provided with polarization electrode 115.In addition, the spontaneous polarization direction of ferroelectric substrate 81 is the thickness direction of ferroelectric substrate 81 as representing with arrow among the figure.Electrode pair 82 is arranged and is arranged in the same one side of ferroelectric substrate 81.In addition, between electrode pair 82, be provided with polarization electrode 115.The the above-mentioned the 1st and the 2nd electric switch is a control polarised direction on the direction on the surface that is parallel to ferroelectric substrate 81, and the 3rd electric switch is the electric switch of control spontaneous polarization direction on respect to the direction of the Surface Vertical of ferroelectric substrate 81.In Figure 13 A and Figure 13 B,, then on direction, also produce electric field with respect to the Surface Vertical of ferroelectric substrate 81 if apply voltage between with electrode 115 at electrode pair 82 and polarization.As ferroelectric substrate 81, used the substrate that on direction, has spontaneous polarization with respect to its Surface Vertical, so shown in Figure 13 C and Figure 13 D, form the different zone 113 of spontaneous polarization, form domain wall 114.In addition, in order to reduce power consumption, be preferably below polarizing and form insulator film with electrode 115.
Figure 14 A～Figure 14 D is the figure of structure of the 4th electric switch of expression embodiments of the present invention 4.Figure 14 A is the vertical view of the structure of expression electric switch, Figure 14 B is the cutaway view of the structure of expression electric switch, Figure 14 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 14 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.The 4th electric switch is formed with electrode pair 82 on the surface of ferroelectric substrate 81, also be provided with polarization electrode pair 125.In addition, the spontaneous polarization direction of ferroelectric substrate 81 is the thickness direction of ferroelectric substrate 81 as representing with arrow among the figure.Electrode pair 82 is arranged and is arranged in the same one side of ferroelectric substrate 81.The surface of the 4th electric switch ferroelectric substrate 81 and the back side are provided with polarization electrode pair 125.The lip-deep polarization that is arranged on ferroelectric substrate 81 is arranged between the electrode pair 82 with one in the electrode pair 125.From the state of Figure 14 A and Figure 14 B, apply electric field by the polarization on the surface that is formed at ferroelectric substrate 81 and the back side with 125 of electrode pairs, become the state shown in Figure 14 C and Figure 14 D.In addition, the spontaneous polarization direction of ferroelectric substrate 81 is with respect to the Surface Vertical of ferroelectric substrate 81.Shown in Figure 14 C and Figure 14 D, form the different zone 123 of polarization 82 of electrode pairs, around it, form domain wall 124.Therefore, make 82 low resistanceizations of electrode pair.In addition, in the 4th electric switch,, preferably make ferroelectric substrate 81 filmings in order to reduce the driving voltage of polarization reversal.The thickness of ferroelectric substrate 81 is preferably below the 5 μ m.
Figure 15 A～Figure 15 D is the figure of structure of the 5th electric switch of expression embodiments of the present invention 4.Figure 15 A is the vertical view of the structure of expression electric switch, Figure 15 B is the cutaway view of the structure of expression electric switch, Figure 15 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 15 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.The ferroelectric substrate 81 of the 5th electric switch is formed with electrode pair 132 for cutting the complementary basis plate on its surface.And then, on ferroelectric substrate 81, also be provided with polarization electrode 135.By applying electric field between with electrode 135 at electrode pair 132 and polarization, the state from the state variation of Figure 15 A and Figure 15 B to Figure 15 C and Figure 15 D.What is called is cut the complementary basis plate, is meant that the spontaneous polarization direction has the substrate of angle with respect to the crystal surface of ferroelectric substrate 81.Because the polarization reversal part is along the direction growth of spontaneous polarization, shown in Figure 15 C and Figure 15 D, different zones 133 direction (direction among the figure shown in the arrow) along spontaneous polarization in the inside of ferroelectric substrate 81 that polarizes is grown.Slipping at the domain wall 134 that forms around the different zone 133 of polarization on the part in the inside of ferroelectric substrate 81 and forming.Since domain wall 134 be present in electrode pair 132 near, so that the resistance low resistanceization of 132 of electrode pairs.
Figure 16 A～Figure 16 D is the figure of structure of the 6th electric switch of expression embodiments of the present invention 4.Figure 16 A is the vertical view of the structure of expression electric switch, Figure 16 B is the cutaway view of the structure of expression electric switch, Figure 16 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 16 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.The 6th electric switch is formed with polarization electrode pair 145 on the surface of ferroelectric substrate 81, replace the polarization electrode of the 5th electric switch shown in Figure 15 A～15D.Be configured to direction and the direction quadrature of polarization that electrode pair 132 is arranged with electrode pair 145 arrangements.By applying electric field with 145 of electrode pairs in these polarization, state that can be from the state variation of Figure 16 A and Figure 16 B to Figure 16 C and Figure 16 D.Under the state shown in Figure 16 C and Figure 16 D, form the different zone 143 of polarization, around it, form domain wall 144.Therefore, make 132 low resistanceizations of electrode pair.
Figure 17 A～Figure 17 D is the figure of structure of the 7th electric switch of expression embodiments of the present invention 4.Figure 17 A is the vertical view of the structure of expression electric switch, Figure 17 B is the cutaway view of the structure of expression electric switch, Figure 17 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 17 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.The 7th electric switch is formed with polarization electrode pair 155 on the surface of ferroelectric substrate 81, replace the polarization electrode of the 5th electric switch shown in Figure 15 A～15D.By applying electric field with 155 of electrode pairs in these polarization, state that can be from the state variation of Figure 17 A and Figure 17 B to Figure 17 C and Figure 17 D.Under the state shown in Figure 17 C and Figure 17 D, form the different zone 153 of polarization, around it, form domain wall 154.Therefore, make 132 low resistanceizations of electrode pair.
The the 5th～the 7th electric switch uses and cuts the complementary basis plate as ferroelectric substrate 81.Thus, domain wall 134,144 and 154 is formed in ferroelectric substrate 132 inside.Therefore, polarization does not directly contact with domain wall 134,144,154 with 155 with electrode pair 145 with electrode 135, polarization.Thus, can significantly reduce from the power consumption that applies electric field of low resistance state when high resistance state moves.
The electric switch of execution mode 4 more than has been described, but has been not limited to the structure of the 1st～the 7th electric switch, so long as just passable in the structure that has electrode pair on the ferroelectric, the polarised direction between them is changed.
In addition, in the explanation of above-mentioned the 1st～the 7th electric switch, omitted explanation and diagram for the electric field applying unit, as long as the polarised direction of electric field applying unit control ferroelectric substrate 81 is can to apply electric field on the direction of polarised direction just passable being opposite to.It for example is the voltage source of explanation in the execution mode 1～3.In addition, can be the mechanism that electrode pair, external power source, electrostatic power sources, discharge, charged particle, ion, other ferroelectrics and semiconductor circuit (for example the electric switch element that is made of semi-conducting material etc.) produce electric field.
In addition, use electrode centering in the polarization of the 2nd, the 4th and the 6th electric switch, the size of each electrode is preferably asymmetrical shape.Be preferably especially, make the electrode of eliminating different spontaneous polarizations bigger than the electrode that forms.Here, the electrode of eliminating different spontaneous polarizations and the electrode of formation are illustrated.The polarization reversal of ferroelectric substrate is to produce polarization reversal nuclear, and polarization inversion unit is from the direction growth of counter-rotating nuclear to spontaneous polarization.LiNbO 3, LiTaO 3, KTP etc. determined the generation direction of polarization reversal nuclear, produces polarization from+Z face side.That is, be formed with polarization reversal and examine a side (at LiNbO 3, LiTaO 3, be+Z side among the KTP etc.) electrode be the electrode that forms different spontaneous polarizations, another electrode is (at LiNbO 3, LiTaO 3, be-Z side among the KTP etc.) be the electrode of eliminating different spontaneous polarizations.
At LiNbO 3, LiTaO 3In the crystallization etc. single polarization, the growth of polarization inversion unit is made of the generation of polarization reversal nuclear and the inversion section operation from the polarization reversal nucleus growth.Polarization reversal is along the growth of the C axle of crystallization, and the generation of polarized nucleus produces in+C side, so polarization reversal takes place to-C from+C.Therefore, polarization is arranged along polarised direction with electrode and is formed, ± it is effective that C axle side forms.At this moment, be preferably make be formed at+electrode of C side than be formed at-electrode shape of C side is little.The width limitations of the inversion section of the spontaneous polarization that forms is in the width of the electrode of+C side.By make apply with the electric field of its elimination-electrode of C lateral electrode ratio+C side is big, can make to eliminate to become more thorough, can increase changes in resistance.In addition, the C axle is a crystal axis, and is identical with the Z axle, the major axes orientation of the crystallization of expression uniaxiality.At LiNbO 3, LiTaO 3, among the KTP etc., the direction of spontaneous polarization is consistent with the C axle.
In addition, as the electrode pair that on the surface of ferroelectric substrate 81, forms, polarization with electrode pair and polarization with the material of electrode, except the metal materials such as Ta, Al, Au, Pt and Cu for example, also can utilize semi-conducting material.In addition, also can on these electrode materials, pile up polysilicon, directly form integrated circuit.
In addition, the ferroelectric material that also can use bulk also can use for example ferroelectric substrate of film as ferroelectric substrate 81.Figure 18 A～Figure 18 D is the figure of structure of the 8th electric switch of expression embodiments of the present invention 4.Figure 18 A is the vertical view of the structure of expression electric switch, Figure 18 B is the cutaway view of the structure of expression electric switch, Figure 18 C is the vertical view of structure of the electric switch of the expression state that produced domain wall, and Figure 18 D is the cutaway view of structure of the electric switch of the expression state that produced domain wall.
Figure 18 A～Figure 18 D is that the ferroelectric substrate 81 of the electric switch shown in Fig. 9 A～Fig. 9 D is film, is formed on the structure on the substrate 167.Move identical with the electric switch of the execution mode 3 shown in Fig. 9 A～Fig. 9 D.As film, can use the epitaxial film made by epitaxial growth, other amorphous film-formings etc.Epitaxial film is owing to utilizing the film with ferroelectric characteristic, so be effective.In addition, as the manufacture method of film, have ferroelectric material is fitted in the method for carrying out thin-film grinding on the substrate.As the method that is fitted on the substrate, the method by bonding agent, direct bonding method etc. are arranged.Behind joint, can grind by CMP and wait the thick ferroelectric film of a few μ m of formation.The method of thin-film grinding is different with the method for carrying out film forming by crystalline growth, is not limited to baseplate material.Therefore, semi-conducting material or dielectric substance etc. as substrate 167, can be formed on any material.If for example will join to as the ferroelectric thin film of ferroelectric substrate 81 on the semiconductor circuit that has formed circuit, then the electric field applying unit that can be had from semiconductor circuit applies voltage to ferroelectric substrate 81, perhaps read the changes in resistance of ferroelectric substrate 81 simultaneously, can constitute ferroelectric memory.
(execution mode 5)
Use accompanying drawing that the electric switch of embodiments of the present invention 5 is illustrated.Electric switch to execution mode 1～4 is illustrated, in execution mode 5, makes electric switch particularly, the result that expression is measured its each characteristic.
Figure 19 is the electric switch of expression execution mode 5 and the schematic diagram of the structure of the experimental system of measuring it.As shown in figure 19, electric switch 170 has: ferroelectric substrate 171; At electrode 172a that forms on the surface of ferroelectric substrate 171 and the electrode 172b that on the back side of ferroelectric substrate 171, forms; Voltage source 174 is as the electric field applying unit that applies electric field between electrode 172a and 172b.In ferroelectric substrate 171, use the LiNbO of the Mg doping of Z plate 3
In order to measure each characteristic, as shown in figure 19, electric switch 170 is immersed in the dielectric 177, between electrode 172a and 172b, apply electric field.Electric switch 170 is immersed in the dielectric 177, is in order to prevent that electric field from applying the discharge in the process.The relation that applies voltage and current between electrode 172a and 172b is measured.In addition, the arrow among the figure is the spontaneous polarization direction of ferroelectric substrate 171.Figure 20 A and Figure 20 B are the graphs of a relation that applies voltage and electric current of the electric switch of Figure 19.In Figure 19, will with the opposed direction of spontaneous polarization as positive direction.That is, in Figure 19, direction from the top down is a positive direction.Figure 20 A makes ferroelectric substrate 171 be undoped LiNbO 3, the graph of a relation that applies voltage and electric current when making its thickness be 0.15mm.In addition, Figure 20 B makes the LiNbO of ferroelectric substrate 171 for the 5mol%Mg that mixed 3, the graph of a relation that applies electric field and electric current when making its thickness be 1mm.
In Figure 20 A, make to apply electric field and increase, when applying voltage and becoming 3.15kV, the counter-rotating of beginning spontaneous polarization.In addition, the electric field that applies of this moment is the 21kV/mm as counter-rotating electric field Ec, if above this value, then have electric current to flow through between electrode 172a and 172b.Electric current stops if the spontaneous polarization of electrode 172a and 172b is reversed fully.Quantity of electric charge Q that flow through this moment and electrode area S and spontaneous polarization Ps are proportional, are the relation of Q=2S * Ps.If again electrode 172a and 172b are applied positive voltage, then there is electric current to flow through equally when reversing again in polarization.This is the general characteristic that ferroelectric shows, and is to take place by the moving of the quantity of electric charge that is accompanied by polarization reversal.
On the other hand, in Figure 20 B, make to apply electric field and increase, when applying voltage and becoming 3.9kV, the counter-rotating of beginning spontaneous polarization.In addition, the electric field that applies of this moment is the 3.9kV/mm as counter-rotating electric field Ec, if surpass this value, then electric current begins to flow through.Because the resistance between electrode 172a and 172b reduces, so electric current continues to flow through.If at the resistance between measurement electrode under this state, then compare with the resistance before the polarization reversal as can be known and reduced by 8 figure places.Then,, become-3.9kV/mm if voltage is reduced, then polarization counter-rotating again, electric current stops.Under this state, stop electric field and apply, the resistance between measurement electrode, the interelectrode resistance of result returns to the value roughly the same with original crystallization.In addition, above-mentioned action is undertaken by the order of " 1 ", " 2 ", " 3 ", " 4 ", " 5 " in Figure 20 B.
In addition, the polarization reversal state partly that produces between electrode 172a at this moment and 172b is observed, the result is represented in Figure 21 A and Figure 21 B.Figure 21 A represent to polarize begin to reverse, the situation of the polarization of the electrode 172a of state that resistance reduces.In addition, Figure 21 B represents that the polarization reversal of having reversed is reversed again, the situation of the polarization of the state electrode 172a of resistance reinstatement.By Figure 21 A as can be known, on a part, there is the different zone of polarised direction 190.In addition, as Figure 21 B as can be known, do not have polarization-reversed region, the direction of polarization all is consistent.The formation of polarization inversion unit and elimination as can be known, relevant with the variation of resistance value between electrode 172a and 172b.That is, the counter-rotating and the non-counter-rotating of the spontaneous polarization by ferroelectric substrate 171 can be controlled the electrical resistance of ferroelectric substrate 171.
And then, owing to can reduce reversal voltage,, be effective therefore so electric switch 170 consumption electric power are less by the filming of ferroelectric substrate 171.For example, when the thickness that makes ferroelectric substrate 171 was the 100nm left and right sides, in the ferroelectric substrate 171 of 3mol%Mg that mixed, reversal voltage was about 1.3V, owing to can carry out low voltage drive, so be effective.Under the situation of ferroelectric substrate 171, several times have been increased than reversal voltage with single crystalline phase for ferroelectric substrate 171 beyond the situation of crystalline substrate, that utilize imperfect crystal formation or microcrystalline state.Therefore, from applying the angle of electric field, the molar concentration that metal adds is preferably more than the 3mol%.In addition, the temperature that applies electric field and crystallization has much relations.Particularly, if make the temperature of ferroelectric substrate 171 rise to 120 ℃, the electric field Ec that then reverses is reduced to approximately general.Therefore, for example electric switch 170 has the heating parts such as heater of heating ferroelectric substrate 171, as long as ferroelectric substrate 171 is heated, just can carry out low voltage drive when carrying out switch.In addition, because the crystal strain that produces when making polarization reversal by heating reduces, so the durability of the number of repetition of electric switch 170 significantly rises.The temperature of the ferroelectric substrate 171 during as switch is preferably more than 20 ℃.In addition, more preferably more than 40 ℃.
In addition, in ferroelectric substrate 171, temperature is same with improving, and irradiation approaches ultraviolet light also can make counter-rotating electric field Ec reduce.As this light wavelength, be preferably below the 500nm, more preferably below the 400nm.By shining this short-wavelength light, can reduce counter-rotating electric field Ec, polarization reversal becomes easily, so can significantly increase the switch number of times, can prolong the life-span of electric switch 170.In addition, eliminating under the situation of the on off state of being stored at one stroke,, can eliminate reliably to noresidue while apply electric field by shining short-wavelength light.
In addition, in common suitable composition, the doping of counter-rotating electric field and Mg is inversely proportional.For example counter-rotating electric field Ec is 21kV/mm under the non-impurity-doped situation, is about 12kV/mm under the situation that 3mol% mixes, and is about 4kV/mm under the situation that 5mol% mixes.Therefore, can control inversion electric field Ec by the adjustment of metal-doped amount.If for example making the thickness of ferroelectric substrate 171 is about 100nm, then under the situation that 5mol% mixes, reversal voltage is 0.4V.If make ferroelectric substrate 171 filmings, the electric field that then reverses further reduces.If the counter-rotating electric field reduces, then can realize high speed motion and highly integrated.But if the counter-rotating electric field is low excessively, then very little interference also can produce counter-rotating and counter-rotating again, can eliminate the data of being stored.So, need to adjust the thickness of ferroelectric substrate 171 and the molar concentration of metallic additions, realize suitable counter-rotating electric field.
As reversal voltage, be preferably the scope of 0.01V～10V.This be because disturb under less than the situation of 0.01V, misoperation that the disturbance meeting makes memory becomes big.Be preferably the amount and the thickness of the metallic additions of adjusting ferroelectric substrate 171, realize reversal voltage in the above range.
In addition, the adjustment of counter-rotating electric field Ec also can be adjusted by the composition of crystallization.Form by making crystallization consist of chemical dose, can significantly reduce counter-rotating electric field Ec.According to actual measurement, very little for the correlation of the molar concentration of Mg, be for about about 4kV/mm between 1～5mol% in doping.Except the amount and the thickness of the metallic additions of above-mentioned ferroelectric substrate 171, also can adjust crystallization and form and realize above-mentioned suitable reversal voltage.
Then, resistance variations that polarization reversal is brought and the doping of Mg are studied.Figure 22 is the molar concentration of the Mg of doping in ferroelectric substrate 171 and the graph of a relation of the changes in resistance amount between electrode 172a and 172b.The electric field in the spontaneous polarization when counter-rotating electric field Ec that reverses increases along with the doping of the Mg of ferroelectric substrate 171 and reduces as can be known.In Figure 22, is not for applying the state (initial condition) of voltage to ferroelectric substrate 171, and ■ is the state (inverted status) of a part of polarization reversal, is the state of ferroelectric substrate 171 low resistanceizations, ▲ be once more the state (inverted status again) of counter-rotating.
As shown in figure 22, when the doping of Mg increased, the changes in resistance amount increased, under the situation of 5mol%, in initial condition, inverted status and inverted status observe the variation of the resistance value of maximum 6 figure places again.According to Figure 22,, need to add the above metal of 1mol% in order to have realized variation as the resistance value more than required 1 figure place of the effect of switch.Be preferably and add more than the 3mol%.At this moment, owing to can realize the variation of the resistance value that 4 figure places are above, so be preferred.
Then, use electric switch 170, measure continuous electric switch characteristic.Use the Mg, thickness of the 5mol% that mixed ferroelectric substrate 171 as 2mm.Temperature is set at 120 ℃.At this moment, reversal voltage is about 4kV.In addition, counter-rotating electric field Ec is about 2kV/mm.Applying voltage limit is maximum ± 6kV, and current value is restricted to maximum 400mA.This measurement result is represented in Figure 23 A and Figure 23 B.Figure 23 A represents to be accompanied by the electrode 172a of effluxion and the voltage waveform between 172b, and Figure 23 B represents to be accompanied by the electrode 172a of effluxion and the current waveform between 172b.In Figure 23 A, be located at voltage that the opposed direction of spontaneous polarization direction with ferroelectric substrate 171 applies for just, be located at the voltage that applies on the spontaneous polarization direction for negative.Equally, in Figure 23 B, be located at the electric current of the opposed direction of spontaneous polarization direction of ferroelectric substrate 171 for just, be located at electric current on the spontaneous polarization direction for negative.In addition, the label of being put down in writing among each figure is represented the same time.
If apply positive voltage (" 2 ", " 8 ", " 14 ", " 20 "), then shown in Figure 23 B, there is electric current to flow through like that, so the resistance between electrode 172a and 172b reduces as can be known above reversal voltage.On the other hand, if apply the required voltage that reverses again following-6kV (" 5 ", " 11 ", " 17 "), resistance increases as can be known, electric current reduces.Can confirm by polarization reversal and reverse again resistance to be reduced and increase.Thereby electric switch 170 is worked as switch as can be known.
In addition, by measuring as can be known, need initialization process in order to use this electric switch 170, and resistance changes in time.At first, below initialization process is described.In ferroelectric substrate 171, before the initial stage that applies electric field, the i.e. pulse of " 1 ", compare with the voltage shown in Figure 23 A, the variation of electric current is less like that shown in Figure 23 B.It is less that this shows that electric field applies the changes in resistance of being brought.That is, under this state (A-stage), resistance is not applying fully variation under the effect of electric field.In order to prevent this from occurring, before using electric switch 170, as long as carry out repeatedly by the switch that applies the polarization reversal that electric field carries out just passable.By doing like this, in ferroelectric substrate 171, can produce and apply the changes in resistance that electric field brings, electric switch 170 can be told switching response.Like this, will electric switch 170 be applied electric field so that the processing of electric switch 170 correct operations is called initialization process repeatedly.
Resistance then is described over time.Shown in Figure 23 B, by applying-pulse of 6kV, make that ferroelectric substrate 171 reverses again, after the high resistanceization, apply under the situation of negative electric field (" 6 ", " 12 ", " 18 "), show as electric current and flow hardly, resistance is very high.But under the situation that applies positive electric field under this state (" 7 ", " 13 ", " 19 "), current value is along with the time increases gradually as can be known.Particularly, current value is 50 μ A under the situation of " 7 ", and current value is 100 μ A under the situation of " 13 ", and current value is 120 μ A under the situation of " 19 ".Like this, under the state that has applied positive electric field, even identical as can be known condition, current value also can increase in time successively.Corresponding with it, resistance also reduces in time.Like this, though do not understand resistance in time and the concrete reason of phenomenon of change, change with certain timeliness of domain wall as can be known or aging relevant.
When constituting memories by electric switch 170, by the counter-rotating of spontaneous polarization, reverse and change resistance again, and read this resistance, differentiate the state of memory thus.In order to differentiate the state of resistance, need apply electric field to polarization inversion unit and differentiate resistance value.By this experimental result as can be known, resistance significantly changes because of having or not polarization reversal, but differentiates resistance in order stably to differentiate resistance, be preferably the electric field that applies with the direction equidirectional of original spontaneous polarization.By Figure 23 B as can be known, can read " 4 " and the resistance difference of " 6 ", the resistance difference of " 10 " and " 12 ", the resistance difference of " 16 " and " 18 ", differentiate resistance by each difference.That is, be preferably under the state of negative electric field (direction identical) and read resistance with spontaneous polarization.Can make changes in resistance big and more stable by reading by negative electric field.In Figure 23 B, if differentiate resistance by positive electric field, if then will be for example " 1 " compare as can be known with the resistance difference of " 15 " with " 13 " with the resistance difference of " 3 ", resistance difference diminishes.Resistance gradually changes like this, and its difference diminishes, so produce error in the differentiation of resistance.
In addition, in execution mode 5,, use the LiNbO of the Mg that mixed as ferroelectric substrate 171 3In addition, at LiTaO 3In also can observe the variation of conductivity by adding metallic additionses such as Mg.Thisly produce the resistance variations that is accompanied by ferroelectric polarization reversal, with the much relations that are configured with of crystallization by adding metal.As ferroelectric substrate 171, be preferably LiNbO 3Affiliated ilmenite structure.As ferroelectric substrate 171, used the MgO:LiNbO of polarization 3, but also can use the ferroelectric that has added metal in addition.For example with added metals such as In, Sc, Cu or Fe, LiNbO 3, LiTaO 3, KTP or their crystallization mixed crystallization, also can access same effect.In other ferroelectric materials, so long as can increase metal-doped amount, the variation that can both produce same electrical conductivity.
As ferroelectric substrate 171, use the ferroelectric crystallization of single polarization, if there is the material of crystal grains such as imperfect crystal formation, crystallite, can both obtain same effect.If utilize amorphous, crystallite structure, then can utilize thin-film material, so do not need the crystalline growth of body, it is easy that the manufacturing of device becomes.In addition,, crystallite amorphous by making can increase the doping of metallic additions, so can increase the changes in resistance amount, are preferred.If,, be difficult to carry out the growth of uniform large-scale crystallization so when the large-scale crystallization of drawing, can produce the crack owing to increase the metal doping amount then the lattice strain increase of crystallization.For example at LiNbO 3Situation under owing to be difficult to add the above Mg of 10mol%, under the situation of using single crystallization base plate, preferably make doping below 10mol%.But, under the situation of amorphous or crystallite structure, can further increase doping.In addition, by use sintering the pottery etc. of crystallite can utilize same characteristic.But, in film, need the boundary line of the spontaneous polarization of reversing in order to form domain wall.Therefore, film needs the crystal grain of certain above size.As crystallite, the size that is preferably crystal grain is more than 1 μ m.As the manufacture method of film, can be methods such as epitaxial growth, MBE, sputter, sol-gel process, laser ablation method.
In addition, can utilize the substrates such as thin film crystallization of materials such as crystallite, amorphous, pottery, single crystals, liquid layer growth, be very important but do when utilizing them that polarization handles.Polarization handle be with temperature increase near the Curie temperature of crystallization, make polarization be directed to a method on the direction by the operation that applies electric field.Because having improved temperature forms spontaneous polarization, so be difficult for residual crystal strain in domain wall.Therefore, when using, preferably use and carried out the substrate that polarization is handled on the direction of an electric field of controlling polarization applying electric field with structure of the present invention.In addition, the short-wavelength light below the illumination wavelength 500 μ m also is effective when polarization is handled.
In addition, in execution mode 5, on ferroelectric substrate 171, formed direct electrode 172a and 172b, can realize low power consumption by between electrode 172a, 172b and ferroelectric substrate 171, forming insulating barrier.In addition, apply electric field and be pulse type, carry out high resistanceization at short notice, also can realize low power consumption by making.
In addition, as ferroelectric substrate 171, be not limited to the substrate of Z plate of the Surface Vertical of spontaneous polarization and ferroelectric substrate 171.Also can utilize for example spontaneous polarization direction and ferroelectric substrate 171 parallel plane X, Y plate or cut complementary basis plate etc. with ferroelectric substrate 171 surfaces have an angle.The polarization of cutting the complementary basis plate is controlled higher, can reproducibility form uniform polarization reversal well, so more preferably.
In addition, by Figure 23 A and Figure 23 B as can be known, in the moment (" 2 ", " 8 ", " 14 ", " 20 ") that polarization reversal takes place with moment (" 5 ", " 11 ", " 17 ") of reversing again takes place, there is a large amount of electric currents to flow through in moment.This is the electric current that produces because of movement of electric charges, and the mobile quantity of electric charge can be represented with 2Ps * S.So-called electric current flows through, and has been meant the 171 low resistance changes of ferroelectric substrate.Also can utilize the low resistanceization of this ferroelectric substrate 171 to make electric switch 170 actions.
In electric switch, be generally electric field as the mechanism of polarization reversal and apply.As the mechanism that changes ferroelectric spontaneous polarization, so long as apply with the mechanism of the opposed electric field of spontaneous polarization, be the mechanism that electrode pair, external power source, static, discharge, charged particle, ion, other ferroelectrics, semiconductor circuit etc. produce electric fields, just can use.In addition, can also make the spontaneous polarization counter-rotating by stress from the outside.By using partly stress application and can control spontaneous polarization such as piezoelectrics.Also can and use in addition with electric field.Can also partly heat, utilize the electric field that produces because of thermoelectric effect to carry out polarization reversal.
In addition, about electrode shape, there is the structure that increases electrical conductivity.As mentioned above, be the part of domain wall because resistance reduces, so the reduction that the area of the domain wall by increasing the polarization reversal periphery can increase resistance.Because formed polarization inversion unit is relevant with electrode shape, so can increase the domain wall area.By using for example comb poles, can increase the area of domain wall.
In addition, in the electric switch of execution mode 1～5, be preferably between electrode that is used for forming polarization and ferroelectric substrate and form dielectric film.Can drive electric switch with low current thus, so can reduce power consumption.
(execution mode 6)
Use the memory element of description of drawings embodiments of the present invention 6.The memory element of execution mode 6 is by any electric switch two-dimensional arrangements in the above-mentioned execution mode 1～5 is constituted.High resistance and low resistance by reading electric switch can realize the function as two dimensional memory.
Figure 24 is the stereogram of structure of the memory element 220 of expression execution mode 6.Memory element 220 is to arrange any electric switch 222 in a plurality of execution modes 1～5 and constitute on semiconductor integrated circuit 221.Semiconductor integrated circuit 221 is made of silicon LSI (large scale integrated circuit), can apply electric field to electric switch 222.By applying electric field the spontaneous polarization direction of the ferroelectric substrate of electric switch 222 is changed, change the electrical conductivity of the part that has applied electric field thus.Because the variation of ferroelectric spontaneous polarization is stable, so also can preserve inverted status even cut-out applies electric field.In addition, can be not from outside supply capability and very stably, through storing for a long time.In addition, can read the state of being stored by the resistance that reads each electric switch 222, even reading state, the state of being stored can not be saved with changing yet.That is, memory element 220 is controlled the electric field that imposes on electric switch 222 by semiconductor integrated circuit 221, carries out the formation or the elimination of spontaneous polarization, comes store status, and detects this state.That is, play a role as memory element.By with electric switch 222 and semiconductor integrated circuit 221 combinations, can realize miniaturization and integrated.
In addition, as the voltage that produces by semiconductor integrated circuit 221, about several V standard, hope can be with low voltage drive.For this reason, electric switch 222 is preferably the structure with ferroelectric thin filmization.As the thickness of ferroelectric substrate, need be for below a few μ m.
But the ferroelectric substrate is understood the acute variation of Yin Wendu and is produced the surface field that is brought by thermoelectric effect.The part of the spontaneous polarization of being stored is disappeared.In order to carry out the operating stably of circuit, need preventing the structure of thermoelectric effect.For example preferably adopt the encapsulating structure that to avoid the temperature acute variation.The serviceability temperature scope is limited in about room temperature ± 50 ℃.In addition, monitor in addition external temperature, for the method for violent variations in temperature start protection circuit.In addition, go up the thermoelectric electric charge that takes place, also have the method that on the ferroelectric substrate surface, forms the film of conductivity in order to eliminate the surface.On a surface, form switch electrode, semiconductor circuit is directly contacted with this face, come driving switch.On a face, pile up the film of conductivity, can prevent the generation of thermoelectric electric charge.
In addition, in the memory element kind of execution mode 6, be preferably to have and be used for heating part that the content of being stored is eliminated together.As the heating part so long as for example heater just can.Heater can make the temperature of the ferroelectric substrate of all electric switches 222 rise.Under the state that the temperature of the ferroelectric substrate that makes all electric switches 222 by heater rises, apply voltage, the ferroelectric substrate is all returned to approach the state of high-resistance original insulator.Be heated to the temperature smaller or equal to Curie temperature, and by applying voltage, eliminate the strain of domain wall, resistance returns to the state that approaches original insulator.As heating-up temperature, be preferably for example more than 200 ℃.In addition, only also can eliminate together by improving temperature.If apply electric field under this state, then polarization is directed to a direction.Apply voltage and can change electrical characteristics by opposite direction from beginning next time, carry out low resistanceization in this direction.
In addition, also can have ultraviolet irradiation portion and replace heater.That is, can ultraviolet irradiation following about wavelength 400nm is just passable to the ultraviolet irradiation portion on the ferroelectric substrate of electric switch 222 as long as have.Penetrate ultraviolet ray from ultraviolet irradiation portion, shine the ferroelectric substrate of all electric switches 222, relax the crystal strain of domain wall, resistance is returned to approach the value of original insulator.Thereby, owing to can make a plurality of electric switch high resistanceization, so the storage of memory element 220 can be eliminated together.
In addition, also can for example and use heating and ultraviolet irradiation.It is above-mentioned that to eliminate as refreshing of resistance together also be effective.Under the situation of the switching characteristic variation that makes each electric switch 222 because of recycling memory element 220,, just can improve switching characteristic as long as refresh.
The difference of the memory element of execution mode 6 and ferroelectric memory in the past is, in the spontaneous polarization direction electrical conductivity of ferroelectric itself is changed, and by electrically detecting this difference, is used as memory element.
Figure 25 is the stereogram of structure of specifically representing the memory element of execution mode 6.As shown in figure 25, on the substrate 237 that is formed with semiconductor integrated circuit, form electrode 232b, form ferroelectric thin film 231 more thereon, more thereon with the electrode 232a of strip formation with electrode 232b quadrature with strip.Constitute memory element by this structure, this memory element is to arrange the electric switch 230 that is made of the ferroelectric thin film 231 that is clipped by electrode 232a and electrode 232b a plurality of and become clathrate.That is, opposed electrode 232a and electrode 232b form an electric switch 230 by clipping ferroelectric thin film 231.And then, though do not illustrate, have the electric field applying unit (not shown) that can apply electric field between opposed electrode 232a and the electrode 232b clipping ferroelectric thin film 231.Use this electric field applying unit, can control the conducting (ON) that is arranged in cancellate electric switch 230 and turn-off (OFF).Particularly, if select any electrode to apply electric field in constituting each of electrode 232a and electrode 232b, then the ferroelectric thin film 231 of the part of selectively electrode 232a and electrode 232b being intersected applies electric field, can change resistance.In addition, by selecting a plurality of electrode 232a and electrode 232b simultaneously, can also once on a plurality of points, write data.In order to read this state, otherwise it is just passable to detect this interelectrode resistance as long as select electrode.
Like this, the memory element of execution mode 6 constitutes easily, and can realize highly integrated.In addition, owing to can write simultaneously, so can significantly improve data processing speed.
As previously discussed, the electric switch of execution mode 1～5 is to have utilized by controlling the characteristic that ferroelectric spontaneous polarization can significantly change electrical conductivity.Particularly, be the counter-rotating that has utilized along with spontaneous polarization, ferroelectric is changed to low-resistance characteristic from high resistance.By this variation, ferroelectric can be changed to semiconductor from insulator.Utilize the electric switch of this characteristic by formation, can constitute the electric switch of high integration with simple structure.
In addition, though spontaneous polarization need apply electric field when counter-rotating, after counter-rotating, do not need electric field.So,,, also can be used as nonvolatile memory so for example pass through to use a plurality of these electric switches because this electric switch can continue to keep this state.
And then if use film as ferroelectric material, the singualtion of then easy realization and semiconductor integrated circuit so can constitute the memory element of high integration, is effective.
The electric switch of execution mode 1～5 and the memory element of execution mode 6 more than have been described, but the structure and materials shown in concrete etc. are an example after all, are not limited to these object lessons.
Industrial applicibility
The memory element of electric switch of the present invention and this electric switch of use can continue to keep The state of storage. Therefore, can be applied to nonvolatile memory, use it storage medium, And comprise in its widely equipment.

Claims (37)

1, a kind of electric switch is characterized in that having:
Added the ferroelectric substrate of metal;
Be arranged on the pair of electrodes on the above-mentioned ferroelectric substrate; And
The electric field applying unit that the polarised direction of the part between above-mentioned pair of electrodes among the above-mentioned ferroelectric substrate is changed,
Add above-mentioned metal in the above-mentioned ferroelectric substrate to and be at least a among Mg, Zn, In, Sc, Cu, the Fe;
By above-mentioned polarised direction is changed, make the resistance change of above-mentioned ferroelectric substrate.
2, electric switch as claimed in claim 1 is characterized in that, above-mentioned ferroelectric substrate is an oxide.
3, electric switch as claimed in claim 1 is characterized in that, above-mentioned ferroelectric substrate is made of the ferroelectric material of single polarization;
Above-mentioned electric field applying unit with the polarised direction of above-mentioned ferroelectric substrate opposed towards on apply electric field.
4, electric switch as claimed in claim 1 is characterized in that, above-mentioned ferroelectric substrate when polarization reversal residual have with above-mentioned counter-rotating after the opposed internal electric field of polarization.
5, electric switch as claimed in claim 1 is characterized in that, above-mentioned electric field applying unit applies electric field to above-mentioned ferroelectric substrate;
Above-mentioned electric field is the AC field of frequency more than or equal to 5Hz.
6, electric switch as claimed in claim 1 is characterized in that, above-mentioned electric field applying unit applies electric field to above-mentioned ferroelectric substrate;
Above-mentioned electric field is the electric field of high frequency ac signal of having superposeed.
7, electric switch as claimed in claim 1 is characterized in that,
Above-mentioned ferroelectric substrate is LiNbO 3
8, electric switch as claimed in claim 7 is characterized in that, above-mentioned ferroelectric substrate is the LiNbO that has added the Z plate of above-mentioned metal 3
9, electric switch as claimed in claim 1 is characterized in that, above-mentioned ferroelectric substrate is the ferroelectric crystallization after single polarization is handled.
10, electric switch as claimed in claim 1 is characterized in that, above-mentioned ferroelectric substrate is crystallite or amorphous materials.
11, electric switch as claimed in claim 1 is characterized in that, above-mentioned pair of electrodes is arranged along the direction of the spontaneous polarization of above-mentioned ferroelectric substrate and formed,
Above-mentioned electric field applying unit is controlled the polarised direction of the part of above-mentioned ferroelectric substrate by apply electric field between above-mentioned pair of electrodes,
Control the resistance between above-mentioned pair of electrodes.
12, electric switch as claimed in claim 11 is characterized in that, also has the pair of electrodes that forms roughly arranging on the direction of quadrature with the spontaneous polarization direction of above-mentioned ferroelectric substrate,
Above-mentioned electric field applying unit is controlled the polarised direction of the part of above-mentioned ferroelectric substrate by apply electric field between the pair of electrodes that forms along above-mentioned spontaneous polarization direction arrangement,
Be controlled at and the spontaneous polarization direction is roughly arranged on the direction of quadrature and resistance between the pair of electrodes that forms.
13, electric switch as claimed in claim 1 is characterized in that, by above-mentioned electric field applying unit above-mentioned ferroelectric substrate is applied electric field, and the polarised direction of 10%～90% part in the above-mentioned ferroelectric part that applies electric field is changed.
14, electric switch as claimed in claim 1 is characterized in that, the direction of the spontaneous polarization of above-mentioned ferroelectric substrate is with respect to the surperficial approximate vertical of above-mentioned ferroelectric substrate.
15, electric switch as claimed in claim 1 is characterized in that, the direction of the spontaneous polarization of ferroelectric substrate is with respect to the surperficial almost parallel of above-mentioned ferroelectric substrate.
16, electric switch as claimed in claim 1 is characterized in that, the maximum resistance of above-mentioned ferroelectric substrate is more than or equal to 100 times of minimum resistance.
17, electric switch as claimed in claim 11 is characterized in that, certain electrode at least of above-mentioned pair of electrodes is a comb poles.
18, electric switch as claimed in claim 17 is characterized in that, above-mentioned ferroelectric substrate is the crystallization of single polarization, the Y direction almost parallel of direction that the electrode of above-mentioned comb poles refers to and above-mentioned crystallization.
19, electric switch as claimed in claim 1, it is characterized in that, above-mentioned electric field applying unit is by the above-mentioned ferroelectric polarised direction of control, form near between above-mentioned pair of electrodes or elimination as the domain wall in the boundary line of different polarised directions, and change resistance value between above-mentioned pair of electrodes.
20, electric switch as claimed in claim 1 is characterized in that, is formed with groove on the surface of above-mentioned ferroelectric substrate, forms above-mentioned pair of electrodes in above-mentioned groove.
21, electric switch as claimed in claim 1 is characterized in that, the interpolation concentration of above-mentioned metal is more than or equal to 1mol% and smaller or equal to 10mol%.
22, electric switch as claimed in claim 1 is characterized in that, the direction of the spontaneous polarization of above-mentioned ferroelectric substrate is with respect to the surface tilt of above-mentioned ferroelectric substrate.
23, electric switch as claimed in claim 1 is characterized in that, the surface of above-mentioned ferroelectric substrate is provided with a pair of polarization electrode,
Above-mentioned electric field applying unit applies electric field at above-mentioned a pair of polarization electricity consumption interpolar.
24, electric switch as claimed in claim 1 is characterized in that, is provided with a pair of polarization electrode in the groove that forms on the surface of above-mentioned ferroelectric substrate,
Above-mentioned electric field applying unit applies electric field at above-mentioned a pair of polarization electricity consumption interpolar.
25, electric switch as claimed in claim 1 is characterized in that, above-mentioned electric field applying unit is the electric switch element that is made of semi-conducting material.
26, electric switch as claimed in claim 1 is characterized in that, has the heating part of the above-mentioned ferroelectric substrate of heating.
27, electric switch as claimed in claim 1 is characterized in that, above-mentioned ferroelectric substrate has the ilmenite structure.
28, electric switch as claimed in claim 1 is characterized in that, the movement of electric charges of the above-mentioned ferroelectric substrate when changing above-mentioned polarised direction flows through electric current between above-mentioned pair of electrodes, make the resistance change between above-mentioned pair of electrodes.
29, electric switch as claimed in claim 1 is characterized in that, above-mentioned ferroelectric substrate has been implemented the direction that makes spontaneous polarization and has handled along the polarization of single direction unanimity substantially.
30, electric switch as claimed in claim 1 is characterized in that, is provided with insulating barrier between at least one and above-mentioned ferroelectric substrate of above-mentioned pair of electrodes.
31, electric switch as claimed in claim 1 is characterized in that, changes by making above-mentioned polarised direction, and above-mentioned ferroelectric substrate is changed to insulator or semiconductor.
32, a kind of memory element is characterized in that,
Have a plurality of as each described electric switch of claim 1 to 31;
Above-mentioned memory element is keeping the resistance value of the above-mentioned ferroelectric substrate of above-mentioned each electric switch.
33, memory element as claimed in claim 32 is characterized in that, above-mentioned each electric switch is arranged with a plurality of two-dimensionally.
34, memory element as claimed in claim 32 is characterized in that, above-mentioned each electric switch is formed with a plurality of on semiconductor integrated circuit;
Above-mentioned electric field applying unit is controlled by above-mentioned semiconductor integrated circuit.
35, memory element as claimed in claim 34 is characterized in that, the resistance value of the above-mentioned ferroelectric substrate of above-mentioned each electric switch is controlled by above-mentioned semiconductor integrated circuit;
The resistance value of the above-mentioned ferroelectric substrate of above-mentioned each electric switch is detected by above-mentioned semiconductor integrated circuit.
36, memory element as claimed in claim 32 is characterized in that, has illumination part;
Above-mentioned illumination part is mapped to the illumination below the wavelength 500nm on the above-mentioned ferroelectric substrate of each electric switch.
37, memory element as claimed in claim 32 is characterized in that, has the heating part with the above-mentioned ferroelectric substrate heating of above-mentioned each electric switch.
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