JP3190907B2 - Single electronic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called single-electron device utilizing a one-electron charging effect, and more particularly to a gate-to-drain-source current caused by a drain-source voltage.
The present invention relates to a single electronic device capable of canceling a shift in voltage dependency between sources.

[0002]

2. Description of the Related Art A so-called single-electron element utilizing the charging effect of one electron is used as a three-terminal switch element similar to a MOSFET which is a mainstream of a switch element in a current semiconductor integrated circuit. In recent years, attention has been paid to the ultimate low power consumption that can control individual devices and the high integration that comes from the fact that the operating principle can be applied to the atomic level. In particular, among single-electron elements, single-electron transistors, which have a simple structure and function as three-terminal switching elements, have been studied for their applicability to logic circuits. FIG. 11 shows an equivalent circuit of a single-electron transistor. As shown in the equivalent circuit of FIG. 11, one island 1 (hereinafter referred to as a conduction island) serving as a localized region of electrons surrounded by a broken line is connected to the conduction island via the tunnel junctions 2 and 3. , 5 (hereinafter, the electrode having a lower potential is referred to as a source electrode 5 and the electrode having a higher potential is referred to as a drain electrode 4), a conductive island 1 and a capacitance (hereinafter, referred to as a drain electrode 4)
This is an electronic device having a structure having at least one control electrode 7 (gate electrode) coupled via a capacitor 6. In the following, the principle of operation of a single-electron transistor according to the present invention will be briefly described. It should be noted that single-electron elements other than single-electron transistors and their operating principles are described, for example, in Single Charge
Tunneling (Plenum Press, 1992, ISBN 0-306-442
29-9).

An important factor in understanding the operation of a single-electron transistor is the change in free energy when one electron enters or exits a conduction island. The change in free energy, the total capacitance C _sigma conductive islands, the gate capacitance C _G, capacitance C _S of the tunnel junction of the source _side, the capacitance C _D of the tunnel junction on the drain _side, the gate - source voltage V _GS, the drain - it can be determined by using the source voltage V _DS. Assuming that V _DS << e / C _} for simplicity, the source electrode 5
When electrons in the conduction islands 1 is a tunnel from the change [Delta] F _S of the free energy from the previous tunnel

(Equation 1) Becomes Where n is the number of electrons in the conduction island before the electrons tunnel. In order for electrons to tunnel from the source to the conduction island, ΔF _S ≧ 0 must be satisfied.
Once an electron tunnels from a source to a conduction island, the process of passing that electron to the drain is more free energy than stopping that electron at the conduction island or entering the next conduction electron. Occurs with the highest probability. In other words, the source, conduction island, drain and electrons move,
Current will flow. Therefore, as can be seen from (Equation 1),

(Equation 2) At this time, current flows (turns ON), and otherwise, no current flows (turns OFF). However, the above discussion has been made on the assumption that the temperature is absolute zero degrees.

When the temperature is finite, the excitation causes V
_{In the case of GS} ≠ e / _CG (1/2 + n), current flows,

(Equation 3) In this case, the current value becomes the smallest because the loss is the highest in free energy. This is shown in FIG. FIG. 12 shows a single-electron transistor having a source capacitance and a drain capacitance of 1 aF each, a source and a drain tunnel resistance of 500 kΩ, a gate capacitance of 3 aF, and an operating temperature of 4.2.
The current flowing between the drain and source of the single-electron transistor when K is expressed as a function of the gate-source voltage _VGS . Thus, the single-electron transistor is simply turned on (or takes the maximum current) when the gate voltage is expressed by (Equation 2), and turned off when the gate voltage is expressed by (Equation 3) ( Or take the minimum current).

[0005]

The object of the invention is to be Solved However, the above discussion is one that has been made on the assumption of V _{DS <<} e / C _Σ. The conduction island of the single-electron transistor is capacitively coupled not only to the gate electrode but also to the source / drain electrode via the tunnel junction. Therefore, there is a disadvantage that the potential of the conductive island easily changes depending on the voltage between the drain and the source, and cannot be controlled only by the control electrode (gate electrode). This is shown in FIG.
FIG. 13 shows the drain-source capacitance of the single-electron transistor when the source capacitance and the drain capacitance of the single-electron transistor are 1 aF each, the tunnel resistance of the source and the drain is 500 kΩ, the gate capacitance is 3 aF, and the operating temperature is 4.2 K. The current flowing between the source and the gate-source voltage V _GS
It is expressed as a function of The drain-source voltage is used as the second parameter. To switch ON and OFF states of the single-electron transistor as described above, it is necessary to shake the gate voltage by _{e / (2C G) = 26.6mV} , when _V DS ~0 _{is V} GS = 0 in most flow hardly OFF state _{current, V GS = e / (2C} G)
With this, an ON state where the current can flow most easily is obtained. However, when the voltage between the drain and the source is increased, the potential of the conductive island shifts, and the maximum value and the minimum value of the current can no longer be obtained at V _GS = 0 and V _GS = e / (2C _G ). In particular, V _DS =
When e / (2C _G ), V _GS = 0 and V _GS = e / (2
In C _G ), the current flowing through the single-electron transistor becomes exactly the same, and the ON state and the OFF state of the single-electron transistor can no longer be controlled by the gate voltage.

On the other hand, as a switching element controlled by a gate electrode, it is desirable to be able to control a state in which a current is most likely to flow and a state in which a current is least likely to flow only by a gate voltage regardless of a potential difference between switches. However, the single-electron transistor is greatly affected by the drain-source voltage as described above, and is turned ON only by the gate electrode.
/ OFF state cannot be controlled. In view of the above, the present invention provides a single unit that can control an ON state (a state where a current has a maximum value) and an OFF state (a state where a current has a minimum value) with only a gate-source voltage, regardless of a drain-source voltage. It is to provide an electronic transistor.

[0007]

According to a first aspect of the present invention, there is provided a first electrode formed on a support substrate, a first insulating film formed on the first electrode, and a first insulating film formed on the first insulating film. The conductive island, a second insulating film formed on the conductive island, a second electrode formed on the second insulating film, and a source that is in tunnel junction with the conductive island and sandwiches the conductive island. A single electronic device comprising: a region and a drain region; and a conductor connecting one of the first electrode or the second electrode to the drain region. According to a second aspect of the present invention, the capacitance between the conductive island and the first electrode, the second electrode, the source region, and the drain region is C _B , C, respectively.
_G, when the _{C S} and _{C D,} a single electronic device according to the first invention, wherein a relationship of _{C G -C B -C D + C} S = 0 holds. The single-electron transistor according to the present invention has at least one or more capacitors and a second (or third, fourth,...) Via a conductive island serving as a localized region of electrons of the single-electron transistor. A gate electrode is added, and the newly added gate electrode is connected to an electrode connected to a conductive island of a single-electron transistor via a tunnel junction. With such a configuration, it is possible to correct the shift of the characteristic of the gate-source voltage dependency of the drain-source current due to the drain-source voltage. As a result, it is possible to supply a single-electron transistor whose ON / OFF state can be controlled by a gate-source voltage regardless of a drain-source voltage. In the simplest case, a single-electron transistor has a second
FIG. 1 shows a configuration example in which one gate electrode is added and the drain electrode is connected to the second gate electrode.

The present invention is, of course, not limited to such a single-electron transistor, but has a conductive island serving as a region where electrons are localized, and utilizes the Coulomb blockade effect or the one-electron charging effect. It can be applied to any device. For example, FIG. 2 shows a configuration example applied to a so-called multi-junction element having four tunnel junctions.
Shown in Here, in FIG. 2, each second conductive island is connected to each second conductive island.
Although all of the gate electrodes are connected to only one electrode connected to one end of the tunnel junction, connecting only one second gate electrode to an electrode connected to one end of the tunnel junction has a remarkable effect. It is possible to obtain Further, a remarkable effect can be obtained similarly in the case where more than two electrodes are connected to the conduction island via the tunnel junction as shown in FIG. Next, a method of optimal design of each capacitance value will be described by taking the case of a single electron transistor as an example. First,
Calculate quantitatively how the application of V _DS shifts the V _GS dependence of I _DS . First, the potential of the conduction island has become V _dot by applying a V _DS.
The change in free energy when electrons enter and exit the conduction island from the source electrode and the number of electrons in the conduction island changes from n to n ± 1 is ΔF _S (n → n ± 1), assuming that the source potential is the ground potential. ,

(Equation 4) Becomes On the other hand, when electrons exit from the conduction island to the drain electrode,
Or the change in free energy upon entry is ΔF _D (n →
n ± 1),

(Equation 5) Becomes

[0009] when applying a positive V _DS, when the current value of the single-electron transistor condition to take a minimum value, equal probability that electrons tunnel to the drain from the probability and conducting island tunnel to the conduction islands from the source is there. Since the tunnel probability is a function of the free energy change ΔF and the tunnel resistance, when the source / drain tunnel resistances are equal, the tunnel probabilities are equal if the free energy changes are equal between the source side tunnel and the drain side tunnel. Therefore, the condition for a single electron transistor to take the minimum current is:

(Equation 6)

(Equation 7) Therefore,

(Equation 8) Becomes Although the case where the _VDS is positive has been described above, the same argument holds true when the VDS is negative. On the other hand, when the potential difference between the second gate electrode and the source connected to the conductive island through the capacitor C _B and V _BS, the potential V _dot of conducting islands can be written as follows.

[0010]

(Equation 9)However, for simplicity, before the electrons tunnel to the conduction island,
Assuming that the initial number of electrons in the conduction island is 0,
The assumptions do not undermine the generality of the following calculations. This
Here, the drain electrode and the second control gate electrode are connected, and V
_BS= V_DSThen, from (Equation 6) and (Equation 7), V
_DSThe shift of the gate voltage characteristic due to _GSIs next
I can write.

[0011]

(Equation 10) Therefore,

[Equation 11] Gate voltage dependence of the shift by the V _DS when satisfying Δ
It can be seen that V _GS can be completely eliminated. As a simple case, consider an example as shown in FIG. 1 in which a second gate electrode is added to a single-electron transistor, and the second gate electrode and the drain electrode are connected. The capacitance between the first gate electrode and the conductive island is equal to the capacitance between the second gate electrode and the conductive island (C _G = C _B ), and the capacitance of the source tunnel junction is equal to the capacitance of the drain tunnel junction ( C
_S = _{C D)} when _it can be seen from equation (9) is one example that can correct the _{V GS-dependent} shift of the _{I DS} by _{V DS.} FIG. 4 shows a computer simulation result of the single-electron transistor according to the present invention having the above-described configuration. FIG. 4 shows that the source capacitance and the drain capacitance of the single-electron transistor are 1 aF, respectively, the tunnel resistance of the source and the drain are both 500 kΩ,
The capacitance of the gate electrode is 2 aF and the capacitance of the second gate electrode is 2
aF and the operating temperature were 4.2K. As shown in FIG.
When the gate voltage of the first gate electrode is 0 V, the single electron transistor is in an OFF state (state in which the current value is minimum), and when the gate voltage is e / (2C _G ), the single electron transistor is in an ON state (maximum current value). ). Of course, the combination of capacitances is not limited to this, and the shift effect can be corrected with any capacitance value as long as the combination satisfies (Equation 9).

Further, the effect obtained by simply connecting the control electrode connected to the conductive island via the capacitor and the electrode connected to the conductive island via the tunnel junction without performing the optimal design for the capacitance value is not as effective. Needless to say, it's big.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment will be described with reference to the drawings. FIG. 5 shows a single-electron transistor according to the present invention, that is, a second gate electrode 14 is provided, two single-electron transistors having the second gate electrode 14 connected to the drain are connected in series, and the charge of the load capacitance 21 is This is a circuit for discharging by these two single electron transistors of the present invention. This circuit represents a two-input NAND circuit which outputs a connection point 25 between a load capacitor 21 and a single electron transistor array. At the input of the logic "0" is zero volts, the logic of the input "1" is represented by e / (2C _G) volts, the output of the logic "0" is zero volts, the logic of the output "1" is accumulated early It is expressed by dividing the charge and the total capacitance of the output node. FIG. 6 shows a simulation result of the circuit of FIG. 5 by a computer. However, the resistance of the tunnel junction of the single electron transistor is set to 50
0 kΩ, a source capacitance of 0.1 aF, and a drain capacitance of 0.1 aF.
1 aF and the gate capacitance were 0.1 aF. The load capacitance _CF was 1 fF, the floating capacitance 22 of the contact connecting the single electron transistors was 5 aF, the temperature was 77 K, and the initial number of charges stored in the load capacitance was 2500 e. However, these values are one of typical values, and it goes without saying that the operation of this circuit is not limited to these parameters. Using the above parameters,
The above-mentioned input voltage is 0V at logic "0" and e / at logic "1".
(2C _G ) to 0.8 V, and the output voltage is 0 with logic “0”.
V, about 2500 e / (C _F ) to 0.4 V at logic “1”
Becomes

As a conventional example corresponding to FIG. 5, a case where a voltage 28 equal to the initial voltage of a load capacitance is applied to a second gate electrode connected to a conduction island of a single-electron transistor via a capacitance (Tacker, Journal)・ Applied ・
Physics, vol. 72, no. 9, p4399-
413, 1992) is shown in FIG. 14, and the simulation result is shown in FIG. As another conventional example, FIG. 16 shows a circuit diagram when a single electron transistor (same as above) having the second control gate grounded is connected in series, and FIG. 17 shows a simulation result thereof. FIG. 18 shows the simulation results of FIGS. 6, 15, and 17 written on the same drawing for easier comparison. As can be seen from FIG. 18, the single electron transistor of the present invention completely maintains the potential of the output load capacitance until the input voltage is applied,
It has excellent characteristics of interrupting current. Also, comparing the discharge characteristics, the characteristic 29 in the case where the fixed voltage is applied to the second gate of the conventional example can discharge only about 60% of the initial voltage, but the single electron transistor of the present invention completely discharges. is made of. Further, it can be seen that the discharge is faster than the characteristic 30 of the conventional example in which the second gate is grounded. This is because, by completely canceling the characteristic shift, the ON state where the maximum current can always flow is effectively corrected. FIG. 19 shows a comparison with the conventional example in a table.

As an example similar to FIG. 5, FIG. 7 shows a case where two single electron transistors of the present invention are connected in parallel, that is, a two-input NOR circuit. This circuit also operates with very high performance, like the circuit of FIG. In the above-described circuit, the same discussion can be naturally made when an electronic device utilizing the Coulomb blockade effect or the single electron charging effect is used instead of the single electron transistor. A second embodiment will be described with reference to the drawings. FIG. 8 shows a single-electron transistor according to the present invention, that is, a second control gate, and two single-electron transistors having the second control gate and the drain connected in series. This is a circuit for charging with these two single electron transistors of the present invention. A third embodiment will be described with reference to the drawings. FIG. 9 is a cross-sectional view of one example of manufacturing a single-electron transistor according to the present invention. Single-electron transistors are called S
MOSFET having ultra-thin silicon layer formed on OI (Silicon-On-Insulator) substrate
Has a structure. Before the formation of the gate insulating film 35, the surface of the ultra-thin silicon layer is roughened by an alkali chemical solution, for example, a choline treatment.

On the silicon surface after the surface treatment, the thickness fluctuation of several nm is repeated at a period of 15 to 40 nm in the plane. In the present embodiment, the silicon layer is extremely thin to 3 nm before performing the chemical treatment. For this reason, the thickness of the silicon film after the chemical treatment becomes 1 nm or less at a thin portion, and a tunnel junction where electrons cannot easily enter is locally formed. After that, the gate insulating film is thermally oxidized or CV
D (Chemical Vapor Deposition)
The single-electron transistor of the present invention can be manufactured by depositing by n) or the like and passing through the same process as a normal MOSFET, and then taking the potential of the substrate and the source or drain in common. FIG. 10 shows an equivalent circuit diagram.

[0017]

According to the present invention, the ON state (the state where the current takes the maximum value) and the OFF state (the state where the current becomes the minimum value) are controlled only by the gate-source voltage regardless of the drain-source voltage. A single electron transistor that can be provided.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of a single-electron transistor in which a second gate electrode is added to a conductive island via a second capacitor, and the second gate electrode and the drain electrode are connected.

FIG. 2 is an equivalent circuit diagram in the case of a multi-junction element having four tunnel junctions.

FIG. 3 is an equivalent circuit diagram in the case of a single electronic device having four tunnel junctions connected to conductive islands.

FIG. 4 is a diagram showing the configuration of FIG. 1 in which the source resistance and the drain resistance are equal, and the gate capacitance and the second gate capacitance are equal ( _CG
= C _B ) and a graph showing the V _GS dependence of I _DS when the source capacitance and the drain capacitance are equal (C _S = C _D ).

FIG. 5 shows a single-electron transistor provided with a second control gate, two single-electron transistors according to the present invention in which the second control gate and the drain electrode are connected in series,
FIG. 3 is an equivalent circuit diagram for discharging a load capacitance.

6 is a graph showing the time dependence of the discharge characteristics of the load capacitance in the equivalent circuit diagram of FIG.

FIG. 7 shows a single-electron transistor provided with a second control gate. Two conventional single-electron transistors having a fixed voltage biased to the second control gate are connected in series,
FIG. 9 is an equivalent circuit diagram for performing a NOR operation by discharging a load capacitance.

FIG. 8 shows a single-electron transistor provided with a second control gate. Two conventional single-electron transistors having a fixed voltage biased to the second control gate are connected in series,
The equivalent circuit diagram which performs an AND operation by charging a load capacity.

FIG. 9 is a cross-sectional view illustrating an example of manufacturing a single-electron transistor according to the present invention.

10 is an equivalent circuit diagram of the single electron transistor of FIG.

FIG. 11 is an equivalent circuit diagram of a conventional single-electron transistor.

FIG. 12 is a graph showing the gate-source voltage dependence of the drain-source current of a single-electron transistor.

FIG. 13 is a graph showing the gate-source voltage dependency of the drain-source current of a single-electron transistor (the drain-source voltage is used as a second parameter).

FIG. 14 shows a single-electron transistor provided with a second control gate. Two conventional single-electron transistors having a fixed voltage biased in cascade are connected to the second control gate to discharge the load capacitance. Circuit diagram for performing a NAND operation by the following.

FIG. 15 is a graph showing the time dependency of the discharge characteristic of the load capacitance in the equivalent circuit diagram of FIG. 14;

FIG. 16 is an equivalent circuit diagram in which a single control transistor is provided with a second control gate, and two conventional single-electron transistors in which the second gate electrode is grounded are connected in series to discharge a load capacitance.

17 is a graph showing the time dependence of the discharge characteristics of the load capacitance in the circuit diagram of FIG.

FIG. 18 is a graph summarizing the simulation results of the output voltages of FIGS. 6, 15, and 17;

FIG. 19 is a comparison table between a conventional single-electron transistor and a single-electron transistor according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Conductive island 2,3 Tunnel junction 4,5 Electrode (or source / drain electrode) connected to conductive island via tunnel junction 6 Capacitor connected to conductive island 7 Control electrode connected to conductive island via capacitor (or 8 Gate-source voltage dependence of drain-source current when drain-source voltage is 1 mV 9 OFF state of single electron transistor 10 ON state of single electron transistor 11 When drain-source voltage is 1 mV Drain-
Gate-source voltage dependence of source current 12 Gate-source voltage dependence of drain-source current when drain-source voltage is 10 mV 13 Gate-source voltage dependence of drain-source current when drain-source voltage is 20 mV Characteristic 14 Second control gate 15 Capacitance between second control gate and conduction island serving as a localized region of electrons 16 Tunnel junction 17 Gate capacitance 18 Single electron according to the present invention when drain-source voltage is 1 mV Gate-source voltage dependence of the drain-source current of the transistor 19 Gate-source voltage dependence of the drain-source current of the single electron transistor according to the present invention when the drain-source voltage is 10 mV 20 The drain-source voltage is 20 mV Of the drain-source current of the single electron transistor according to the present invention at the time of - source voltage dependency 21 the load capacitance 22 stray capacitance 23 Input A 24 Input B 25 output node 26 input A of the logic tree of the logic tree output node, the input voltage waveform 27 waveforms to the output node of the logical tree to B. The initial charge of the output node is 2500 elementary charges. The single-electron transistor is the single-electron transistor of the present invention, and the second control gate is short-circuited to the drain. 28 Power supply biasing the second control gate with a fixed voltage (initial voltage at output node) 29 Waveform to output node of logic tree. The initial charge of the output node is 2500 elementary charges. The single-electron transistor is a conventional single-electron transistor in which the second control gate is biased to a fixed voltage. 30 Waveform to output node of logic tree. The initial charge of the output node is 2500 elementary charges. The single-electron transistor is a conventional single-electron transistor, and the second control gate is grounded. Reference Signs List 31 power supply voltage to logic tree 32 silicon substrate 33 insulating film on silicon substrate 34 silicon on insulating film (SOI) 35 gate insulating film 36 gate electrode 37 interlayer insulating film 38 metal wiring 39 thin film silicon roughened by chemical treatment channel

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/66 H01L 29/06

Claims (2)

(57) [Claims] A first electrode formed on the support substrate; a first insulating film formed on the first electrode; a conductive island formed on the first insulating film; and a conductive island formed on the conductive island. The second insulating film, a second electrode formed on the second insulating film, and a tunnel junction with the conductive island, and
A single electronic device comprising: a source region and a drain region sandwiching the conductive island; and a conductor connecting one of the first electrode or the second electrode to the drain region. 2. When the capacitance between the conductive island and the first electrode, the second electrode, the source region and the drain region is C _B , C _G , C _S and C _D , respectively, C _{G -C B -C D + C S =} 0 single electronic device according to claim 1, wherein is established that the relationship expression.