JP2005039103A - Quantum mechanical switching method and device by metal atom/ metal cluster - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure high speed switching with any reduced limitation of electrode metal and an operation environment. <P>SOLUTION: An atmospheric pressure scanning tunnel microscope system is used, and Pt/Ir is used for a probe 2 as one electrode. A silver fine particle deposition film 6 is formed by dropping a dispersion solution obtained by dispersing silver fine particles being a metal cluster in acetone onto a graphite substrate 4 as the other electrode, and evaporating the acetone. Thereafter, the probe 2 is forced to approach the silver fine particle deposition film 6, and feedback is made off, voltage operation is performed by a power supply device 8, and a current change and a conductance change are measured by an ampere meter 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to fabrication of nanometer-scale ultra-fine structures represented by the current semiconductor industry, and more particularly to a quantum mechanical switch method and apparatus for performing nanocontact using a metal atom or metal cluster in which quantized conductance appears. It is.

Conventional nanocontact in the region where the quantized conductance appears has been performed using metal atoms, mainly noble metals (Au, Ag, Cu, etc.).
One is the generation of atomic bridges by mechanically bringing a gold probe into contact with each other in an ultrahigh vacuum (see Non-Patent Document 1). In this paper, a gold STM (scanning tunneling microscope) probe is brought into contact with the surface of a sample obtained by depositing gold on a thin copper wire, and gold atoms formed when a constant voltage is applied between the probe and the sample. The conductance is measured while observing the change of the cross-linking with a TEM (transmission electron microscope), thereby associating the structure of the gold atom cross-linking with the conductance. FIG. 4 shows a TEM image of how the atomic bridge becomes narrower by separating the probes in the order of (a) to (f). The upper and lower black triangular objects are the STM probe and the sample surface, and an atomic bridge is formed between them, and the atomic bridge disappears in (f). FIG. 5 shows a state in which the conductance decreases stepwise as the STM probe and the sample surface move away. FIGS. 5 (a) to (f) are the same as FIGS. 4 (a) to 4 (f). It corresponds to the state.

  On the other hand, a method for controlling the generation / extinction of atomic bridges using an electrochemical reaction in a solution has also been reported (see Non-Patent Document 2). In that paper, an STM probe (Pt / Ir) covered with wax on the surface of a gold substrate placed in a copper sulfate solution was approached to an interval of 10 to 150 nm, and then each of the probe and the substrate By controlling the oxidation / reduction reaction of copper ions or copper atoms by manipulating the electrode potential of copper, a copper atom bridge is formed between the electrodes and is eliminated. FIG. 6 is a conceptual diagram of the experimental system. The formation / disappearance of the copper atom bridge can be confirmed by a change in the interelectrode current.

Furthermore, there is an experimental example in which the conductance between the electrodes is observed by directly moving the metal cluster between the electrodes by using a cantilever of an atomic force microscope (AFM) to form a nanocontact (see Non-Patent Document 3). . First, the surface of the sample is observed with AFM, and the positions of the electrodes (Ti / Au: SiO ₂ surface after Ti is evaporated and Au is evaporated) and gold nanoparticles are confirmed. Then, turn off the feedback, bring the AFM probe near the back of the nanoparticle to be moved, and push and move the nanoparticle on the side surface of the AFM probe in the direction to move. After moving the nanoparticles, turn the feedback on and observe the image again to confirm the movement of the nanoparticles. This operation is repeated until the nanoparticles are moved to a desired position (FIGS. 7A to 7D). FIG. 8 shows a change in current when a voltage of 1 mV is applied between the electrodes and the nanoparticle is “intruded” and “extruded” between the electrodes repeatedly. As a result, a sudden increase in current is observed after the particles are pushed into the electrode, the resistance value between the electrodes at that time becomes 100Ω, and then the current becomes zero when the particles are pushed out of the electrode. As described above, switching control for turning on / off the bonding / non-bonding between the metal electrode and the metal nanoparticles is realized by the mechanical position manipulation of the nano-sized fine particles.

On the other hand, there is one research example that uses a solid electrolyte (for example, Ag ₂ S) to control the generation / extinction of atomic bridges by voltage manipulation (see Non-Patent Document 4). In this case, movement and precipitation of metal atoms in the solid electrolyte are used, and the quantized conductance can be sufficiently controlled. However, it is essential to make the electrode with a solid electrolyte.
Kunio Takayanagi, Yukito Kondo, Hideaki Onishi, Applied Physics 69, 10, 1215, (2000) CZ Li and NJ Tao, Appl. Phys. Lett., 72 (1998) 894. L. Samuelson, et.al, Appl. Phys. Lett., 72 (1998) 548 T. Hasegawa et.al.RIKEN Review 37 (2001) 7. Yugo Kawabata, Journal of the Physical Society of Japan, Vol. 55, No. 4, page 256

The formation of nanocontacts using the metal wires and metal clusters described above basically requires an ultra-high vacuum system.
In addition, the nanocontact control is based on the mechanical operation of both electrodes or the mechanical operation of the metal cluster, and requires a fine movement mechanism on the nanometer scale.

Electrochemical preparation requires an electrolyte solution.
When switching using nano-contact is performed, the on / off speed is extremely slow due to the mechanical operation as described above, and it does not serve as a switch.
In the atomic wire construction using the solid electrolyte, the switching speed is considered to be sufficiently fast, but it is necessary to use a solid electrolyte such as Ag ₂ S as the electrode.

  It is an object of the present invention to provide a quantum mechanical switching method and apparatus that can be switched at high speed with few restrictions on the electrode metal and the operating environment.

  In the quantum mechanical switching method of the present invention, metal electrodes facing each other with a gap are arranged in the vicinity of separable metal atoms or metal clusters, and the gap between the metal electrodes is connected by the metal atoms or the metal clusters for quantization. By setting the magnitude of a current flowing in units of conductance, and performing intermittent switching of voltage application between the metal electrodes or switching of the polarity of the applied voltage, the quantized conductance due to the metal atoms or metal clusters between the metal electrodes is changed. The nano-contact that generates a unit current is generated and extinguished.

  In contrast to the conventional nanocontact control technology described above, the present invention operates by simply arranging metal atoms or metal clusters between the electrodes, regardless of the element of the electrode metal. Also, regarding the operating environment, temperature adjustment is essentially unnecessary regardless of whether it is in ultra-high vacuum, atmospheric pressure or in solution.

  In the nanocontact control method of the present invention, an appropriate metal atom or metal cluster is arranged between electrodes close to a nanometer scale, for example, several to several hundreds of nanometers. To achieve contact at the atomic level of metal atoms or metal clusters and electrode metal, that is, nanocontact.

  The quantum mechanical switching device of the present invention that realizes this quantum mechanical switching method includes a metal atom or a metal cluster that can move separately from each other, and a current in units of quantized conductance that is connected by the metal atom or metal cluster. An opposing metal electrode arranged at an interval capable of generating a flowing nano-contact, and intermittent application of voltage between the metal electrodes so as to cause generation and disappearance of the contact by the metal atom or metal cluster between the metal electrodes or And a power supply device for switching the polarity of the applied voltage.

Metal clusters are classified into various particle sizes and are commercially available. As the metal atom, commercially available metal particles adsorbed on the surface by vacuum deposition can be used.
The voltage applied to the metal electrode by the power supply device can be several volts or less, and the switching speed of the voltage application to the metal electrode by the switching power supply device can be set to 100 kHz or more.

The present invention generates a contact state on an atomic scale by changing applied voltage between both electrodes at high speed in a simple environment in which metal atoms or metal clusters are arranged between electrodes brought close to a nanometer size. -An atomic switch that uses nanocontacts to disappear. Moreover, it can be realized at room temperature and pressure.
As a result, energy saving, process complexity reduction, and device construction based on a new method are expected for conventional semiconductor switches.

FIG. 1 is an outline of an apparatus for realizing the method of the present invention.
In the experiment, an atmospheric pressure scanning tunneling microscope system is used, and the probe 2 as one electrode is made of an alloy of Pt / Ir (Pt (80%) / Ir (20%)). Usually, Pt is segregated on the surface. Is used). On the graphite substrate 4 as the other electrode, a dispersion liquid in which silver fine particles having a particle size of 30 to 150 nm (nano silver: a product of NANO TNC, Korea), which is a metal cluster, are dispersed in acetone is dropped to evaporate the acetone. Thus, a silver fine particle deposition film 6 is formed. Then, after the probe 2 was brought close to the silver fine particle deposition film 6 and the feedback was turned off, voltage operation was performed by the power supply device 8 and current change and conductance change were measured by the ammeter 10.

  FIG. 2 shows the measurement results. The voltage applied between the electrodes 2 and 4 is shown in the upper part, and the observed conductance is shown in the lower part. The horizontal axis is time (seconds). When the sample voltage is plus 0.5 V, a tunnel current (about 1 nA) flows, but when the sample voltage is raised to plus 2 V, the current increases rapidly.

When this current was examined in detail, some of the changes were stepped. That is, it can be seen that it is quantized, and shows the formation of cross-links in atomic units. This data shows a nanoconductance value of 1G ₀ , which is quantized as will be apparent from the following explanation of quantized conductance, and shows a constant quantized conductance during voltage application. I understand that. This quantum number n is not necessarily 1, and depending on the position on the sample surface, n takes various values on the order of one digit. Even if the voltage square wave is repeatedly applied, the value of the quantized conductance is reproducible.

Here, the phrase “quantized conductance” will be described. Landauer's theory is often used to discuss the electronic conductivity of one-dimensional electron systems (see Non-Patent Document 5, for example). According to this, the conductance of the one-dimensional electron system that does not interact is 2e ² / h (e is the charge of the electron, and h is the Planck's constant) in the absence of electron scattering. This value is called quantized conductance and is a universal value independent of the system. Usually, it is often expressed as G = nG ₀ T (n is a positive integer) by multiplying by the transmission coefficient T, where G ₀ is a prime quantity of quantized conductance (1 / 12.4) S (S is Siemens) It is. Aside from organic molecules and the like, T is almost 1 in metal, so when nanocontact occurs like atomic bridge, conductance is quantized and shows discrete values.

  FIG. 3 shows an example in which the quantized conductance by nanocontact is measured by increasing the switching speed by controlling the quantized conductance by increasing the speed of applied voltage change. The waveform indicated by the symbol Vs represents the applied voltage, and the waveform indicated by the symbol C represents the conductance value associated therewith. This is a change in conductance when 6 waves of a square wave of ± 1.5 V and 40 kHz are applied as the applied voltage Vs. A bridge is formed when the applied voltage Vs is positive, and the applied voltage Vs disappears when the applied voltage Vs is negative. You can see that

  As shown in this example, when the polarity of the applied voltage Vs having the same absolute value is changed, when the applied voltage Vs can form a bridge in the positive region and disappear in the negative region, the switching of the polarity is more reliably performed. Control becomes possible.

In addition, the switching speed is a single trial both when the bridge is formed and when the bridge is extinguished, but a fast response up to 0.3 μs, that is, 300 MHz has been confirmed. It is certain to be.
Since FIG. 1 shows a configuration at the experimental stage, a flat plate is used as one of the electrodes 4. However, when the device is formed as a switch, the electrode shape may be appropriately changed depending on the application. .

  The quantum mechanical switching method and apparatus of the present invention can be used as a low-voltage, low-power consumption microminiature switch that is inexpensive and easy to manufacture. A relay switch can be formed by tripolarizing the electrodes. Moreover, there is a possibility that it can be used for a volatile memory because of its operation principle.

It is a perspective view which shows the electrode part in one Example roughly. In one Example, it is a figure which shows the mode of the change of the conductance between electrodes when the voltage of a square wave is applied. It is a figure which shows the conductance change when six continuous waves are applied to the square wave of ± 1.5 V and 40 kHz in the same embodiment. In the conventional method, a change in the gold atom bridge formed when a gold STM probe is brought into contact with the surface of a sample obtained by depositing gold on a thin copper wire and a constant voltage is applied between the probe and the sample is separated. It is the TEM image which showed the mode. It is a figure which shows the conductance change corresponding to the state of FIG. It is a conceptual diagram of the experimental system which produces | generates an atomic bridge | crosslinking using an electrochemical reaction in a solution in the conventional method. It is an AFM image which shows a mode that a metal cluster is moved between electrodes by the cantilever of AFM and a nanocontact is formed in the conventional method. It is a figure which shows an electric current change when a voltage is applied between electrodes in the method of FIG. 7, and the pushing-in of the nanoparticle between electrodes and the extrusion from an electrode are repeated.

Explanation of symbols

2 Probe 4 Graphite substrate 6 Silver fine particle deposition film 8 Power supply

Claims (7)

A metal electrode facing each other with a gap in the vicinity of metal atoms or metal clusters that can be separated from each other, and connecting the gaps between the metal electrodes with the metal atoms or the metal clusters to flow a current in units of quantized conductance. The contact of the voltage between the metal electrodes is switched or the polarity of the applied voltage is switched, so that a current in units of a quantized conductance by the metal atom or metal cluster flows between the metal electrodes. A quantum mechanical switching method characterized by causing generation and annihilation. The quantum mechanical switching method according to claim 1, wherein generation and disappearance of the nanocontact are performed under atmospheric pressure. Metal atoms or metal clusters separable from each other;
Opposite metal electrodes arranged at intervals capable of generating nanocontacts through which currents in units of quantized conductance are connected by the metal atoms or metal clusters;
A power supply device for intermittently applying a voltage between the metal electrodes or switching the polarity of the applied voltage so as to cause the generation and disappearance of the contact between the metal electrodes or the metal clusters between the metal electrodes. Quantum mechanical switch device. The quantum mechanical switching device according to claim 3, wherein the metal atoms or metal clusters are arranged under atmospheric pressure. The quantum mechanical switching device according to claim 4, wherein the metal atom or metal cluster is disposed in the air. The quantum mechanical switch device according to any one of claims 3 to 5, wherein a voltage applied to the metal electrode by the power supply device is several volts or less. The quantum mechanical switch device according to any one of claims 3 to 6, wherein a switching speed of a voltage applied to the metal electrode by the power supply device is set to 100 kHz or more.