JP2003282893A - Double-tunnel junction element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double-tunnel junction element exhibiting a negative differential resistance, in a double-tunnel junction having a flexible structure. <P>SOLUTION: The double-tunnel junction element having a flexible structure, is provided with a first electrode 1 made of a conductive metal, a conductive semiconductor, or a conductive organic material, a second electrode 2 made of a conductive metal, a conductive semiconductor, or a conductive organic material, each intermediate electrode 3 for functioning as a Coulomb island which is made of metal molecules, semiconductor molecules, or organic molecules, a first barrier layer 4 having a flexible structure, each second barrier layer 5 having a flexible structure which is so existent between the second electrode 2 and each intermediate electrode 3 as to become a barrier for electrons and holes, and a double-tunnel junction comprising the first electrode 1, the first barrier layer 4, the intermediate electrodes 3, the second barrier layers 5, and the second electrode 2 which are arranged in this order. By this structure, in the state of applying a voltage across the first and second electrodes 1, 2, the perturbation of the Coulomb force caused by the going-in and going-out of electrons or holes so resonates with the mechanical natural frequency of each intermediate electrode 3 that the tunnel current flowing through the double-tunnel junction exhibits a negative differential resistance. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double tunnel junction element having a flexible structure, and more particularly to a negative differential resistance element applied to a functional element.

[0002]

2. Description of the Related Art Heretofore, an Esaki diode, which has a negative differential resistance by using a tunnel phenomenon, has been used.
Resonant tunnel diodes have been proposed and applied to ultra-high speed functional devices. These diodes are
Both are characterized by utilizing the distribution of electronic levels in the energy direction.

By the way, recently Gorelik et al.
ys. Rev. Lett magazine (Vol.80, 4526-
4529, 1998), in a double tunnel junction having a flexible structure, the Coulomb force on the intermediate electrode changes due to the temporal change in the amount of charge of the intermediate electrode acting as a Coulomb island. We propose a so-called electronic shuttle, in which the tunnel resistance is modulated by the mechanical vibration of the and electric charges are transferred between the electrodes.
This electron shuttle phenomenon is a new single-electron element that combines mechanical vibration and single-electron phenomenon, and its realization of current standard and its application to functional elements are being studied.

[0004]

However, it was not expected that a negative differential resistance would appear in the current-voltage dependence of the element exhibiting the electron shuttle phenomenon.

In view of the above situation, it is an object of the present invention to provide a double tunnel junction element which exhibits a negative differential resistance in a double tunnel junction having a flexible structure.

[0006]

In order to achieve the above object, the present invention provides [1] a double tunnel junction element having a flexible structure,
A first electrode made of a conductive metal, semiconductor or organic material and a second electrode made of a conductive metal, semiconductor or organic material
An electrode, an intermediate electrode made of a metal, a semiconductor, or an organic molecule that functions as a Coulomb island, and a barrier between electrons or holes that exists between the first electrode and the intermediate electrode,
A first barrier layer having a flexible structure, which is present between the second electrode and the intermediate electrode and serves as a barrier against electrons or holes;
A second barrier layer having a flexible structure, the first electrode, a first barrier layer, an intermediate electrode, a second barrier layer, and a double tunnel junction in which a second electrode is arranged in this order. When a voltage is applied between the first electrode and the second electrode, the perturbation of the Coulomb force due to the entry and exit of electrons or holes between the first electrode and the intermediate electrode and the mechanical natural vibration of the intermediate electrode are It is characterized by having a structure in which the voltage dependence of the tunnel current flowing through the double tunnel junction exhibits negative differential resistance due to resonance.

[2] In a double tunnel junction element having a flexible structure, a first electrode made of a conductive metal, semiconductor or organic material, a second electrode made of a conductive metal, semiconductor or organic material, and Coulomb A metal that functions as an island,
An intermediate electrode composed of a semiconductor or an organic molecule; a first barrier layer having a flexible structure, which is present between the first electrode and the intermediate electrode and serves as a barrier against electrons or holes; A second barrier layer having a flexible structure, which is present between the intermediate electrodes and serves as a barrier against electrons or holes; the first electrode, the first barrier layer, the intermediate electrode, and the second barrier layer; Second
Electrons or holes entering the intermediate electrode from the first electrode from the intermediate electrode with a voltage applied between the first electrode and the second electrode. Resonance between the perturbation of the Coulomb force caused by being transferred to the second electrode and the mechanical natural vibration of the intermediate electrode causes the voltage dependence of the tunnel current flowing through the double tunnel junction to produce a negative differential resistance. It is characterized by having a structure to be expressed.

[3] In the double tunnel junction device according to the above [1] or [2], the voltage dependence of the tunnel current of the double tunnel junction has a peak.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

FIG. 1 is a schematic diagram of a negative differential resistance element having a double tunnel junction having a flexible structure according to the present invention.

In this figure, 1 is a first electrode made of a conductive metal, a semiconductor or an organic material, 2 is a second electrode made of a conductive metal, a semiconductor or an organic material, 3 is a metal functioning as a Coulomb island, Intermediate electrodes made of a semiconductor or organic molecule, 4 is a first barrier layer having a flexible structure, which is present between the first electrode 1 and the intermediate electrode 3 and serves as a barrier against electrons or holes, and 5 is a second electrode. It is a second barrier layer having a flexible structure, which is present between 2 and the intermediate electrode 3 and serves as a barrier against electrons or holes.

The tunnel junction between the first electrode 1 and the intermediate electrode 3 is called a first junction, and the tunnel junction between the second electrode 2 and the intermediate electrode 3 is called a second junction.

According to the present invention, in the double tunnel junction having a flexible structure, the first electrode 1 or the second electrode 2 and the intermediate electrode 3 are provided.
Resonance between the perturbation of Coulomb force due to the entry and exit of electrons or holes and the mechanical natural vibration of the intermediate electrode 3.
Alternatively, the perturbation of the Coulomb force caused by the transfer of the electrons or holes entering the intermediate electrode 3 from the first electrode 1 to the second electrode 2 and the mechanical natural vibration of the intermediate electrode 3 may occur. The most significant feature is to provide a negative differential resistance element having a structure in which the voltage dependence of the tunnel current flowing through the double tunnel junction causes a negative differential resistance by resonating.

That is, according to the present invention, a first electrode 1 made of a conductive metal, a semiconductor or an organic material, a second electrode 2 made of a conductive metal, a semiconductor or an organic material, and a metal functioning as a Coulomb island, An intermediate electrode 3 made of a semiconductor or an organic molecule, and a first barrier layer (first junction) 4 existing between the first electrode 1 and the intermediate electrode 3 and having a flexible structure which serves as a barrier against electrons or holes. And the second electrode 2
And a second barrier layer (second junction) 5 which is present between the intermediate electrode 3 and serves as a barrier against electrons or holes and has a flexible structure.
In the double tunnel junction in which the first electrode 1, the first barrier layer 4, the intermediate electrode 3, the second barrier layer 5, and the second electrode 2 are arranged in this order, the first electrode 1 and the second electrode 2 When a voltage is applied between the first electrode 1 and the intermediate electrode 3, the perturbation of the Coulomb force caused by the entry and exit of electrons or holes between the first electrode 1 and the intermediate electrode 3 resonates with the natural vibration of the intermediate electrode 3. Alternatively, the perturbation of the Coulomb force caused by the transfer of the electrons or holes entering the intermediate electrode 3 from the first electrode 1 to the second electrode 2 and the mechanical natural vibration of the intermediate electrode 3 may occur. By resonating, the double tunnel junctions 4, 5
There is a peak in the voltage dependence of the tunnel current flowing through the.

Incoming and outgoing and transfer of electrons or holes between the electrodes 1 and 2 and the intermediate electrode 3 in the present invention occur as follows. Generally, in the tunnel junction, the tunnel junction between the first electrode 1 and the intermediate electrode 3 is referred to as the first junction 4, and the tunnel junction between the second electrode 2 and the intermediate electrode 3 is referred to as the second junction 5. E. Hanna and M.D. Tin
Kham et al. in Phys. Rev. B magazine (Vol 4
4, 5919-5922, 1991), the tunnel rate at each junction is

[0016]

[Equation 1]

It is expressed as follows. However, ΔEj is the energy change of the junction j corresponding to the increase or decrease of the unit charge in the intermediate electrode 3,

[0018]

[Equation 2]

It is expressed as follows.

Here, C1 and C2 are capacitances of the first junction 4 and the second junction 5, R1 and R2 are tunnel resistances of the first junction 4 and the second junction 5, T is an absolute temperature, and Q is an intermediate electrode 3. The above charge amount, Q0 is a compensation charge, kB is a Boltzmann constant, e is a unit charge, and V is a voltage applied to the second electrode 2 with the first electrode 1 as a reference. The probability that n electrons are present in a minute dot is the distribution coefficient σ (n) [where Σσ
(N) = 1], and the above equation is converted into the following rate equation σ (n) [Γ ₁ ⁺ (n) + Γ ₂ ⁺ (n)] = σ (n + 1) [Γ ₁ ⁻ (n + 1) + Γ ₂ ⁻ (n +
1)], the distribution coefficient σ (n) can be obtained.
From the distribution coefficient σ (n), the time average electron number N (V) on the intermediate electrode 3 is obtained as follows.

[0021]

[Equation 3]

When Coulomb blockage occurs in the double tunnel junction, the time average electron number N (V) is quantized and takes an integer value. By the way, in the region where N (V) is not an integer, between the smallest integer Na that is larger than N (V) and the largest integer Nb that is smaller than N (V). The number of charges on the intermediate electrode 3 goes in and out. The frequencies f1 and f2 of charge in and out of the intermediate electrode 3 at the first junction 4 and the second junction 5 are

[0023]

[Equation 4]

It becomes

Here, it is assumed that the tunnel resistance R1 is smaller than R2. In general, time average electron count N
The voltage dependence of (V) depends on the tunnel resistance ratio, and the larger the ratio of R1 and R2, the more the number of electrons on the intermediate electrode 3 is quantized by Coulomb blockage. Therefore, here R2 / R
It is assumed that 1 is 10 or more, more preferably 100 or more. At this time, f1 becomes larger than f2, and f1
Then, a phenomenon occurs in which electric charges flow in and out of the intermediate electrode 3. In the electrode system including the first electrode 1, the intermediate electrode 3, and the second electrode 2, an electrostatic force (Coulomb force) is periodically applied to the intermediate electrode 3 due to the inflow and outflow of the charge, and the intermediate electrode 3
Will oscillate along the external electric field generated between the first electrode 1 and the second electrode 2. When the frequency dependence of f1 is calculated, f1 has a maximum value when the fractional part of the number N (V) of time-averaged electrons is 0.5.

The frequency of charge transfer when electrons or holes entering the intermediate electrode from the first electrode are transferred to the second electrode from the intermediate electrode, and electrons entering the intermediate electrode from the second electrode Or the frequency of charge transfer when holes are transferred from the intermediate electrode to the first electrode is

[0027]

[Equation 5]

As described above, either f4 or f5 is obtained.

Here, it is assumed that the tunnel resistance R1 is smaller than R2, as in the case where charges flow in and out of one of the junctions, and that R2 / R1 is 10 or more, more preferably 100 or more. F4 when the voltage is positive
Becomes larger than f5, and a phenomenon in which charges are transferred at f4 occurs, and when the voltage is negative, f4 becomes f5
Therefore, a phenomenon in which charges are transferred at f5 occurs. In the electrode system including the first electrode 1, the intermediate electrode 3, and the second electrode 2, the Coulomb force is periodically applied to the intermediate electrode 3 by the transfer of the charges, and the intermediate electrode 3 is
It vibrates along the external electric field generated between the electrode 1 and the second electrode 2. Calculating the frequency dependence of f4 and f5 increases the absolute value of the voltage, and when the voltage is negative, f4 is constant in the voltage region below the voltage V at which N (V) is approximately equal to Nb. And when the voltage is positive,
F5 is constant in a voltage region equal to or higher than the voltage V at which N (V) is almost equal to Na.

On the other hand, in the double tunnel junction including the flexible structure in the portion supporting the intermediate electrode 3, the intermediate electrode 3 has a frequency f3 at which it mechanically resonates, and this f3 is f ₃ = 1 / 2π√ It is given by (k / M). Here, k is the apparent spring constant of the system supporting the intermediate electrode 3, and M is the apparent mass of the resonance system including the intermediate electrode 3.

Here, if the frequency f1 of mechanical excitation due to the Coulomb force caused by the charge and discharge of electric charges to and from the intermediate electrode 3 and the mechanical natural resonance frequency f3 match, the intermediate electrode 3 vibrates greatly due to resonance. Become. This intermediate electrode 3
Of the first junction 4 and the tunnel distance of the second junction 5
Modulate the tunnel distance of.

In general, the tunnel resistance changes exponentially with respect to the tunnel distance, and the tunnel rate increases as the tunnel distance decreases. Therefore, the modulation of the tunnel distance due to the vibration of the intermediate electrode 3 causes the modulation of the tunnel resistance, and the electric charge is transferred in synchronization with the mechanical vibration of the intermediate electrode, that is, the so-called electronic shuttle phenomenon causes the tunnel current to flow to the external circuit. It becomes easy to flow.

As described above, in the double tunnel junction having a flexible structure, when the average number of electrons on the intermediate electrode 3 has a value below the decimal point, the charge and the output cause the mechanical force by the Coulomb force. When there is excitation and the excitation frequency matches the natural resonance frequency of the intermediate electrode 3, the amplitude of the intermediate electrode 3 becomes large due to resonance, and the electron shuttle phenomenon is easily observed. Furthermore, the mechanical excitation frequency due to this Coulomb force depends on the Coulomb blockade phenomenon, and therefore has voltage dependence, and since the tunnel current increases in the voltage region where the electron entrance / exit frequency and the natural frequency of the intermediate electrode resonate, Negative differential resistance will be observed in the dependence of the current and voltage flowing through the external circuit.

Further, the perturbation frequency f4 or f5 of the Coulomb force caused by the transfer of electrons or holes entering the intermediate electrode 3 from the first electrode 1 to the second electrode 2 and the intermediate electrode 3 When the mechanical natural vibration frequencies f3 match, the amplitude of the intermediate electrode 3 increases due to resonance,
The so-called electron shuttle phenomenon, in which charges are transferred in synchronization with vibration, becomes easy to observe. Furthermore, the mechanical excitation frequency due to this Coulomb force depends on the Coulomb blockade phenomenon and therefore has voltage dependency, and since the tunneling current increases in the voltage region where the electron transfer frequency and the natural frequency of the intermediate electrode resonate, Negative differential resistance will be observed in the dependence of the current and voltage flowing through the external circuit.

The tunnel resistance R1 is the tunnel resistance R2.
Frequency f of electron ingress and egress, assuming smaller than
The maximum value of 1 and the frequency f4 or f5 corresponding to the transfer of electrons are as follows. When the change in the number of charges in the intermediate electrode 3 is the same, the maximum value of the frequency f1 of electron inflow and outflow is larger. Is higher than the frequency f4 or f5 corresponding to.

Further, the voltage dependence of f1 has a maximum value, whereas f4 or f5 monotonically increases with an increase in the absolute value of the voltage, and when the voltage is negative, N (V Is substantially equal to Nb in a voltage range equal to or lower than V, and when the voltage is positive, f4 is substantially constant in a voltage range equal to or higher than V in which N (V) is substantially equal to Na. Therefore, the resonance with the mechanical natural frequency of the intermediate electrode 4 will be observed both when the charge goes in and out and when the charge is transferred.

Although it is assumed that the tunnel resistance R1 is smaller than the tunnel resistance R2 in the initial state, the resonance causes the amplitude to increase and the intermediate electrode 3 to move to the second position.
When there is a moment when the tunnel resistance R1 becomes larger than the tunnel resistance R2 when approaching the electrode 2, a charge having a polarity opposite to that of the charge transferred before the amplitude becomes large due to resonance from the second electrode 2. Entering the intermediate electrode 3, the intermediate electrode 3
The electron shuttle may be observed in the so-called returning process in which the electron is transferred when the electron approaches the first electrode 1.

Further, the intermediate electrode 3 may be made of metal, fine semiconductor particles, or organic molecules as long as it has a size and an electrostatic capacity such that the Coulomb blockade phenomenon can be observed. When using semiconductors and organic molecules,
Since there are discrete electronic levels, the Coulomb blockade phenomenon is affected by the electronic levels. However, even if the intermediate electrode 3 is a semiconductor, even if the intermediate electrode 3 is a semiconductor It may be a molecule.

The flexible structure in the first barrier layer 4 and the second barrier layer 5 between the first junction and the second junction may be such that the portion supporting the intermediate electrode 3 has a flexible structure. That is, since the intermediate electrode 3 may be supported by at least one barrier layer having a flexible structure, one of the joints may be a space in which a vacuum or gas exists.

In the flexible structure of the present invention, in the vibration system including the intermediate electrode 3 and the first barrier layer 4 and the second barrier layer 5 including the flexible structure, the number of charges existing on the intermediate electrode 3 causes resonance of the vibration system. A material or structure that changes the tunnel resistances R1 and R2 when changing in synchronization with the frequency is preferable, and an organic material or a liquid is preferable as the material.

Specific examples of the double tunnel junction element of the present invention will be described below.

FIG. 2 is a block diagram of a double tunnel junction device showing a specific example of the present invention.

In this figure, 11 is a mica substrate and 12
Is a gold film [gold (111) crystal plane], 13 is a 1,6 hexanedithiol self-assembled film on the gold film 12, and 14 is an average particle diameter of the 1,6 hexanedithiol self-assembled film 13. 8 nm colloidal gold fine particles (commercially available product: perfect metal manufactured by vacuum metallurgy), 15 is a scanning probe. In this structure, the scanning probe 15 includes the first electrode 1, the gold film 12 includes the second electrode 2, the gold fine particles 14 include the intermediate electrode 3, the hexanedithiol self-assembled film 13 includes the second barrier layer 5, and the scanning probe 15. The space between the gold particles 14 corresponds to the first barrier layer 4.

A gold film 12 was deposited on the mica substrate 11 and heat-treated to obtain a gold (111) crystal plane. This gold film 12
A 1,6 hexanedithiol self-assembled film 13 was formed on the attached mica substrate 11, and colloidal gold fine particles 14 having an average particle size of 8 nm were implanted. The element in which the colloidal gold fine particles 14 and the mica substrate 11 with the gold film 12 are chemically bonded by two thiol groups is put in a vacuum, and the scanning probe (tungsten probe) 15 is brought close to it, and the current-voltage characteristic at the time of probe vibration is measured. did. As a result, the tungsten probe 1
5, the applied voltage is 0.17V, 0.23V,
At 0.3 V and 0.35 V, a clear negative differential resistance was observed.

FIG. 3 is a diagram showing a measurement result showing negative resistance (peak) by the double tunnel junction element of the present invention, and FIG. 3 (a) is a positive bias side showing negative resistance (peak). 3B is a diagram showing the measurement result on the negative bias side in which the negative resistance (peak) appears. In these figures, the horizontal axis represents voltage and the vertical axis represents current.

The negative resistance (peak) in FIG. 3 is
This is because resonance between the excitation system and the natural vibration of the intermediate electrode due to the entry and exit or transfer of electrons occurs in the plurality of intermediate electrodes 3. The simultaneous occurrence of the resonance phenomenon in the plurality of intermediate electrodes means that the double tunnel junction according to the present invention can be used in parallel, and from the viewpoint that the device current can be increased. preferable.

This measurement was carried out when the probe was vibrated. The probe frequency was several orders of magnitude lower than the mechanical resonance frequency f3, and the distance between the scanning probe and the fine gold particles was modulated. It ’s just that. Furthermore, when the voltage dependence was measured without vibrating the probe, the same current peak was observed as the current-voltage characteristic at the same position as in FIG.

The present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0049]

As described above in detail, according to the present invention, in a double tunnel junction having a flexible structure, a single electron or a single hole can enter and exit between one electrode and an intermediate electrode. Resonance between the perturbation of the resulting Coulomb force and the mechanical natural vibration of the intermediate electrode makes it possible to develop a negative differential resistance of the tunnel current flowing through the double tunnel junction.

The present invention can be used as a device having a negative differential resistance generally used in electronic circuits, and includes an oscillator, a trigger circuit, an identification circuit for identifying and outputting an input data signal, and an ultra-high speed digital signal. -It can be used for functional devices such as shift registers and ultra-high speed devices.

[Brief description of drawings]

FIG. 1 is a schematic view of a negative differential resistance element including a double tunnel junction having a flexible structure according to the present invention.

FIG. 2 is a configuration diagram of a double tunnel junction element showing a specific example of the present invention.

FIG. 3 is a diagram showing a measurement result in which a negative resistance (peak) appears by the double tunnel junction element of the present invention.

[Explanation of symbols]

1st electrode 2 Second electrode 3 intermediate electrode 4 First barrier layer (first junction) 5 Second barrier layer (second junction) 11 Mica substrate 12 Gold film [gold (111) crystal plane] 13 1,6 Hexanedithiol self-assembled film 14 Colloidal gold particles 15 Scanning probe (tungsten probe)

Claims (3)

[Claims] 1. A double tunnel junction element having a flexible structure, wherein (a) a first electrode made of a conductive metal, semiconductor or organic material and (b) a first electrode made of a conductive metal, semiconductor or organic material. Two electrodes, (c) an intermediate electrode composed of a metal, a semiconductor, or an organic molecule that functions as a Coulomb island, and (d) a barrier existing between the first electrode and the intermediate electrode for electrons or holes. A first barrier layer having a flexible structure, and (e) a second barrier layer having a flexible structure, which is present between the second electrode and the intermediate electrode and serves as a barrier against electrons or holes, ( f) A double tunnel junction in which the first electrode, the first barrier layer, the intermediate electrode, the second barrier layer, and the second electrode are arranged in this order, and (g) the first electrode and the second electrode. Electrons between the first electrode and the intermediate electrode are applied with a voltage applied between the electrodes. Resonance between the perturbation of the Coulomb force due to the entrance and exit of holes and the mechanical natural vibration of the intermediate electrode causes the voltage dependence of the tunnel current flowing through the double tunnel junction to exhibit a negative differential resistance. A double tunnel junction device having a structure. 2. A double tunnel junction element having a flexible structure, wherein (a) a first electrode made of a conductive metal, semiconductor or organic material and (b) a first electrode made of a conductive metal, semiconductor or organic material. Two electrodes, (c) an intermediate electrode composed of a metal, a semiconductor, or an organic molecule that functions as a Coulomb island, and (d) a barrier existing between the first electrode and the intermediate electrode for electrons or holes. A first barrier layer having a flexible structure, and (e) a second barrier layer having a flexible structure, which is present between the second electrode and the intermediate electrode and serves as a barrier against electrons or holes, ( f) A double tunnel junction in which the first electrode, the first barrier layer, the intermediate electrode, the second barrier layer, and the second electrode are arranged in this order, and (g) the first electrode and the second electrode. With the voltage applied between the electrodes, the electric current from the first electrode into the intermediate electrode The voltage of the tunnel current flowing through the double tunnel junction due to the resonance of the Coulomb force perturbation caused by the transfer of the child or the hole from the intermediate electrode to the second electrode and the mechanical natural vibration of the intermediate electrode. A double tunnel junction device having a structure in which the dependence exhibits a negative differential resistance. 3. The double tunnel junction element according to claim 1 or 2, wherein the voltage dependence of the tunnel current of the double tunnel junction has a peak.