JP3607943B2 - Optical input / current output device using photo-induced phase modulation of charge density wave - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching element or a memory element, and more particularly to a light input / current output type switching element or memory element using light-induced phase modulation of a charge density wave.
[0002]
[Prior art]
Most of the optical input / current (voltage) output type devices use a photocurrent due to semiconductor band-to-band excitation or a photoelectric effect, such as a photodiode or a photoconductive cell. Since such an element simply replaces light energy with electric energy as it is, a non-linear circuit is separately required to exhibit an on / off switch function.
[0003]
In addition, the phototransistor has an on / off switch function by light, but there is no function of recording information in the element itself, and a separate memory circuit or memory element is required to record on / off information. .
[0004]
Further, although the charge coupled device and the magneto-optical recording device have a memory function in the device itself, a specific output circuit or a magnetic detection device is required to read out information.
[0005]
[Problems to be solved by the invention]
On the other hand, with the development and practical application of information and communication processing using light, such as the development of information communication networks using optical fibers, the development of optical computers and optical neurocomputers, etc., it is easy to record optical information and output it as electronic information And a simple switching method of an electronic circuit using an optical signal are required.
[0006]
However, when an optical element such as a conventional phototransistor or a magneto-optical recording element is used, an additional circuit or an additional device is required as described above, and there is a problem that it is not suitable for handling a huge amount of optical information instantaneously. is there.
[0007]
Therefore, the present invention has been made in view of the above-described conventional problems, and an opto-electric switching element and a memory element suitable for processing optical information without requiring an additional circuit or an additional element. Its purpose is to provide.
[0008]
That is, in contrast to the above-described conventional technology, in the present invention, light directly acts on the electronic state of a material exhibiting a charge density wave state, and as a result, the electric conduction state of the substance is changed greatly. An input / current output type memory or switch is realized. The objective of optical / electrical conversion is achieved with the simplest circuit configuration without requiring an intermediate circuit or an intermediate material for converting information.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a light input / current output element formed of a material capable of light-induced phase modulation of a charge density wave, comprising a pair of electrodes formed on a surface of the light input / current output element. An optical input / current output element having a light irradiation part formed between the electrodes is provided. The material is selected from the group comprising K _0.30 MoO ₃ , Rb _0.30 MoO ₃ , (K _1-X Rb _X ) _0.30 MoO ₃ , NbSe ₃ , TaSe ₃ , and a layered transition metal chalcogenide. A light input / current output element which is a material to be processed. Further, the light input / current output element has a condensing means for irradiating the light irradiation unit with an optical signal in the vicinity of the light irradiation unit.
[0010]
An element according to the present invention is an optical switching element formed of a material capable of photoinduced phase modulation of a charge density wave, and includes a pair of electrodes formed on a surface thereof and a light formed between the pair of electrodes. A first state comprising a state where a charge density wave formed by applying a predetermined voltage between the pair of electrodes is distorted and light irradiation to the light irradiation unit. An optical switching element having a second state in which distortion of the charge density wave disappears.
[0011]
An element according to the present invention is an optical memory element formed of a material capable of photoinduced phase modulation of a charge density wave, and is formed between a pair of electrodes formed on a surface thereof and the pair of electrodes. A first state formed by distortion of a charge density wave formed by applying a predetermined voltage between the pair of electrodes, and light irradiation to the light irradiation unit. An optical memory element having a second state in which the first state has disappeared.
[0012]
Furthermore, the present invention provides an optical switching element formed of a material capable of light-induced phase modulation of a charge density wave, and having a pair of electrodes formed on a surface thereof and a light irradiation portion formed between the pair of electrodes. ,
A first step of applying a predetermined voltage between the pair of electrodes to form a state in which a charge density wave is distorted in the substance and bringing the electrodes into a conductive state; and light irradiation to the light irradiation unit And a second step of eliminating the distorted state of the charge density wave.
[0013]
The present invention relates to an optical memory element formed of a material capable of photoinduced phase modulation of a charge density wave, and having a pair of electrodes formed on the surface thereof and a light irradiation part formed between the pair of electrodes. ,
By applying an on-pulse having a first voltage equal to or higher than a predetermined voltage between the pair of electrodes, a state in which a charge density wave is distorted is formed in the substance, and a first state in which conduction between the electrodes is possible A step of forming a second state in which the distortion of the charge density wave is eliminated by irradiating the light irradiation unit with off-pulse light; and a second lower than the first voltage between the pair of electrodes. Applying a signal pulse having a voltage to detect whether the memory element is in the first state or the second state, and storing predetermined information in the memory element Is the method.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. The following description is an example of the present invention and is intended to illustrate the general principle of the present invention, and the present invention is limited to only the configuration specifically described in this embodiment. It is not a thing. In the following detailed description and in the drawings, like elements are designated with like reference numerals.
[0015]
The operation of the charge density wave device will be described below.
The charge density wave state refers to a state in which the density of electrons changes in a spatially constant cycle in a metal exhibiting one-dimensional or two-dimensional electrical conduction, and accordingly the lattice is distorted in the same cycle. The charge density wave is often abbreviated as CWD (charge density wave).
[0016]
A charge density wave can be driven by an electric field to conduct electricity. This corresponds to a state in which many localized electron clouds are collectively moving. On the other hand, the movement of the charge density wave is hindered by a local potential change due to lattice defects or impurity atoms. The state in which the movement of the charge density wave is prevented is usually expressed as “pinned”, in which case the movement of the electron cloud is blocked.
[0017]
When the charge density wave is pinned, the electron cloud cannot move and no current flows in a weak electric field, but the pinning is lost and the electron cloud starts moving above a certain electric field. This state is expressed as “slip” with respect to the crystal lattice of the density wave.
[0018]
In a material in a charge density wave state, “slip” on the crystal lattice of the density wave mainly contributes to the current. By the way, the phase of the density wave is spatially pinned by impurities or lattice defects that are inevitably present in the normal material as described above. In order to induce the “slip”, a certain level of voltage (Sh require the application of the threshold voltage V _t). Since the current increases rapidly when the applied voltage exceeds V _t , this type of material exhibits essentially non-linear conductivity.
[0019]
Furthermore, different likelihood of slippage by the phase modulation pattern of the charge density wave, thus V _t are different. For example, once a slip occurs, the pattern changes to a pattern in which current easily flows, and thereafter, V _t decreases (V _t at this time is expressed as V _tv ).
[0020]
Next, when light is irradiated, V _t increases by smoothing the modulation pattern that has been deformed into a pattern in which the current easily flows (V _t at this time is expressed as V _tp ). Thus, the threshold voltage has an effect of memorizing the presence or absence of light irradiation.
[0021]
The present invention controls this nonlinearity and memory effect of the material by light. That, V _t is increased by smoothing the phase modulation of the density wave by light, and using that this effect is maintained even after the light irradiation, in which to the switch and memory operations.
[0022]
FIG. 1 is a schematic diagram of a charge density wave device 1 of the present invention and a circuit device for explaining the operation thereof. In the present invention, as shown in FIG. 1, a pair of electrodes 3 and 4 are provided on the surface of a substance 2 showing a charge density wave state constituting the charge density wave device 1, and a voltage applied by a voltage generator 5 is provided on the surface. A switching or memory function is realized by selecting the magnitude and order of the amount of light supplied from the light collecting means 6 such as a lens.
[0023]
FIG. 2 is a diagram showing the structure of the charge density wave device 1 according to the embodiment of the present invention, in which a pair of electrodes 3 and 4 are provided on the surface of a crystal piece 7 of a substance showing a charge density wave state having a front surface and a back surface, A light irradiation unit 12 is provided between the pair of electrodes 3 and 4. As a substance exhibiting a charge density wave state, K _0.30 MoO ₃ was used. Rb _0.30 MoO ₃ or _{(K 1-X R b X} ) can also be used _0.30 M o O _3. In addition, a quasi-one-dimensional metal such as NbSe ₃ or TaSe ₃ can be used, and a layered transition metal chalcogenide can also be used. If necessary, an antireflection film can be formed on the surface of the light irradiation unit 12.
[0024]
The thickness of the crystal piece is not particularly limited, but may be about 1 to 100 μm. In this embodiment, the distance between the electrodes 3 and 4 is 25 μm and the electrode width is 50 μm, but the present invention is not limited to this value. As the electrodes 3 and 4, a silver thin film formed by mask vapor deposition was used.
[0025]
In the switch operation, as shown in FIG. 3, the state (i) where the density wave is flowing is irradiated with light (ii) to smooth the phase modulation pattern of the density wave to stop the slip, and the current between them is reduced. It can be blocked (iii).
[0026]
FIG. 4 shows the voltage-current characteristics of the charge density wave device shown in FIG. A solid line is a characteristic in a state where no light is irradiated, and a dotted line is a characteristic when light having a wavelength of 532 nm is irradiated with 56 mW / cm ² of steady light on the element surface. In the embodiment shown in FIG. 4, the voltage at which the current rises is 0.75 v when light is not irradiated, but is 0.97 v when light is irradiated. Therefore, if an intermediate voltage between these electrodes 3 and 4 is applied, for example, 0.85 to 0.9 V, this element can be switched depending on the presence or absence of light irradiation.
[0027]
The difference in impedance between the electrodes when irradiated with steady light (56 mW / cm ² ) is shown below.
Voltage between electrodes Without light irradiation With light irradiation 0.85v 31.1 MΩ 1.55 GΩ
0.90v 4.29MΩ 1.06GΩ
Since the threshold voltage (voltage at which the current rises) when no light is irradiated is determined by impurities or lattice defects in the crystal, it can be generally controlled by controlling the impurity concentration. An easier artificial control is to change the composition ratio of the crystal so that lattice distortion occurs. FIG. 5 shows the threshold electric field (E _T (V / cm)) change of (K _1-X Rb _X ) _0.30 MoO ₃ when potassium (K) is replaced with rubidium (Rb).
[0028]
As described above, the phase modulation pattern of the charge density wave is displaced to a pattern in which current easily flows after slipping. This modulation pattern is preserved even when the voltage is removed. Therefore, thereafter, V _t decreases and the threshold value becomes V _tv . On the other hand, when the light is irradiated, the modulation pattern of the density wave is smoothed and the modulation pattern generated by the slip is eliminated, so that the threshold value increases and becomes V _tp . Thus, the charge density wave device has a function of memorizing the presence or absence of light irradiation. That is, the state in which V _t is decreased by energization or the state in which V _t is increased by light irradiation continues until the next application of an external field that causes the reverse process. It operates as a memory that is maintained without any special operation.
[0029]
An example of the operation of the charge density wave device 1 as a memory in the circuit configuration shown in FIG. 1 is shown in FIG. Reference numeral 5 denotes a pulse voltage generator. As an input voltage, a voltage pulse equal to or higher than V _tp (hereinafter referred to as an on-pulse) and a voltage pulse satisfying V _tv <V <V _tp (hereinafter referred to as a signal pulse) are shown in FIG. As shown in a), it occurs at a predetermined cycle.
[0030]
That is, FIG. 6A shows a case where a plurality of signal pulses are generated after generating an on pulse of V _tp or more as an input voltage. Reference numeral 13 is a reference resistor for detecting the output current of the charge density wave device 1. The voltage across the reference resistor 13 is observed with an oscilloscope 14. A light pulse (hereinafter referred to as an “off pulse”) having a predetermined period from an optical signal supply means (not shown) is applied to the surface of the charge density wave device 1 through the light collecting means 6.
[0031]
As the off pulse, it is necessary to irradiate the operation surface of the charge density wave device with light having an energy density of at least 8.4 mJ / cm ² . In this case, since the total amount of energy becomes a problem for the modulation of the phase of the charge density wave, for example, by applying 8.4 mJ / cm ² of energy with picosecond pulse light, a high inversion speed of picosecond can be realized. . In this case, if the distance between the electrodes is 25 μm and the width of the electrodes is 50 μm, this corresponds to injecting a total amount of light energy of 100 nJ between the electrodes. On the contrary, if necessary, the state can be changed by irradiating very weak light for a long time.
[0032]
FIG. 6B and FIG. 6C show the relationship between the off pulse and the output current when the off pulse is irradiated. FIG. 6B shows that by applying an off pulse immediately after application of an on pulse, an off state in which a subsequent signal pulse does not appear as an output current is maintained until the next on pulse is applied.
[0033]
FIG. 6C shows a state in which the signal pulse is blocked by the off pulse after passing one signal pulse after the on pulse. In any case, both the on and off states are cleared by the off pulse and the on pulse, respectively, and the state is maintained until cleared.
[0034]
FIG. 7 is a diagram showing a second structural example of the charge density wave device 1 of the present invention. For example, a thin film 9 of a material showing a charge density wave state such as Rb _0.30 MoO _{3 is} formed on the surface of the single crystal sapphire substrate 8 with a thickness of 0.5 μm, for example. The formation of the thin film 9 is not limited to this method, but it is preferable to use a laser ablation method. By using the laser ablation method, when using Rb _0.30 MoO ₃ or the like that requires a strict definition of the composition ratio as the charge density wave material, the composition ratio of the formed thin film matches the composition ratio of the raw material. It becomes possible to make it. The thickness of the thin film can be about 0.1 to 1 μm. The thin film 9 is formed so as to have anisotropy, and therefore, a single crystal substrate such as the sapphire substrate 8 is used. As the other substrate, a semiconductor single crystal substrate can be used. The electrodes 3 and 4 can be formed by lithography other than mask vapor deposition.
[0035]
FIG. 7 shows an example in which an optical fiber 10 having a tapered tip 11 is used instead of the lens shown in FIG. It is preferable to deposit a metal thin film on the tip portion 11 to increase the reflectance at the surface.
[0036]
Although only one charge density wave device is shown in FIG. 7, actually, a plurality of charge density wave devices are arranged on the substrate 8 in, for example, a linear form or a matrix form. In this case, the thin film is separated by, for example, chemical etching to form individual charge density wave elements 1. If necessary, another optical element such as an optical logic element can be formed on the substrate 8.
[0037]
Although several embodiments of the present invention have been illustrated and described above, the embodiments of the present invention described herein are merely examples, and various embodiments can be made without departing from the technical scope of the present invention. It is clear that deformation is possible.
[0038]
Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, at least one of the problems described in the column of the problem to be solved by the invention can be solved, and is described in the column of the effect of the invention. In the case where at least one of the existing effects is obtained, an effect obtained by deleting this constituent element can be extracted as an invention.
[0039]
【The invention's effect】
As shown in FIGS. 3 and 6, in the present invention, by using the nonlinearity inherent in the substance and the reset effect that light brings to the density wave, the current is turned on in a state where the density wave is flowing constantly. · as an off optical switch, also by leaving the absence of Kosoto field was caused changes in V _t, it acts as a memory that stores the value of the changed V _t.
[0040]
According to the present invention, a substance capable of light-induced phase modulation of a charge density wave can be used as an optical switch element or a memory element without providing an external circuit as a single substance.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a charge density wave device 1 of the present invention and a circuit device for explaining its operation.
FIG. 2 is a view showing a structural example of a charge density wave device 1 of the present invention.
FIG. 3 is a diagram showing a switch operation by light irradiation.
FIG. 4 is a diagram showing voltage-current characteristics of a charge density wave device.
FIG. 5 is a diagram showing a change in threshold electric field (E _T (V / cm)) for (K _1-X Rb _X ) _0.30 MoO ₃ .
FIG. 6 is a diagram illustrating an example of an operation of a charge density wave device as a memory.
FIG. 7 is a diagram showing a second structural example of the charge density wave device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Charge density wave element 2 ... Material which shows a charge density wave state 3 ... Electrode 4 ... Electrode 5 ... Pulse voltage generator 6 ... Condensing means 7 ... Crystal piece 8 ... Sapphire substrate 9 ... Thin film 10 ... Optical fiber 11 ... Tip Unit 12 ... Light irradiation unit 13 Reference resistance 14 Oscilloscope

Claims (6)

_{K 0.30 M o O 3, R} b 0.30 M o O 3, (K 1-X R b X) 0.30 M o O 3, N b S e 3, T a S e 3 and layered, A light input / current output element formed of a material selected from a group including a transition metal chalcogenide, a pair of electrodes formed on a surface thereof, and a light irradiation unit formed between the pair of electrodes, An optical input / current output element comprising: The light input / current output element according to claim 1, further comprising a condensing unit for irradiating the light irradiation unit with an optical signal in the vicinity of the light irradiation unit. _{K 0.30 M o O 3, R} b 0.30 M o O 3, (K 1-X R b X) 0.30 M o O 3, N b S e 3, T a S e 3 and layered, An optical switching element formed of a material selected from a group including a transition metal chalcogenide having a pair of electrodes formed on a surface thereof and a light irradiation portion formed between the pair of electrodes. ,
The first state, in which the charge density wave formed by applying a predetermined voltage between the pair of electrodes is distorted, and the distortion of the charge density wave disappeared by the light irradiation to the light irradiation part. An optical switching element having a state of 2. _{K 0.30 M o O 3, R} b 0.30 M o O 3, (K 1-X R b X) 0.30 M o O 3, N b S e 3, T a S e 3 and layered, An optical memory element formed of a material selected from the group containing transition metal chalcogenides, comprising a pair of electrodes formed on the surface thereof, and a light irradiation part formed between the pair of electrodes. ,
The first state, in which the charge density wave formed by applying a predetermined voltage between the pair of electrodes is distorted, and the distortion of the charge density wave disappeared by the light irradiation to the light irradiation part. An optical memory device characterized by having a state of 2. _{K 0.30 M o O 3, R} b 0.30 M o O 3, (K 1-X R b X) 0.30 M o O 3, N b S e 3, T a S e 3 and layered, In an optical switching element having a pair of electrodes formed on a surface thereof and a light irradiation part formed between the pair of electrodes, formed of a material selected from a group including a transition metal chalcogenide of
A first step of forming a state in which a charge density wave is distorted in the substance by applying a predetermined voltage between the pair of electrodes and bringing the electrodes into a conductive state;
And a second step of eliminating distortion of the charge density wave state by irradiating the light irradiating unit with light. _{K 0.30 M o O 3, R} b 0.30 M o O 3, (K 1-X R b X) 0.30 M o O 3, N b S e 3, T a S e 3 and layered, In an optical memory element having a pair of electrodes formed on a surface thereof and a light irradiation portion formed between the pair of electrodes, formed of a material selected from a group including a transition metal chalcogenide of
By applying an on-pulse having a first voltage equal to or higher than a predetermined voltage between the pair of electrodes, a state in which a charge density wave is distorted is formed in the substance, and a first state in which conduction between the electrodes is possible Steps,
Enabling the formation of a second state in which the distortion of the charge density wave is eliminated by irradiation of off-pulse light to the light irradiation unit;
Applying a signal pulse having a second voltage lower than the first voltage between the pair of electrodes to detect whether the memory element is in the first state or the second state; A method for storing predetermined information in the memory element.

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