JPH1093028A - Quantum effect element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inject desired electrons or holes in basic cells and hold this state by forming a basic cell layer and conductive layer connected to electrodes through an insulating layer or energy barrier layer of a fixed thickness on the upper and lower side of the basic cell layer. SOLUTION: A first Si oxide insulating layer 2 of several nanometers thickness is formed on a first n-type Si conductive layer 1 and quantum boxes 6 of several nanometers at one side each are formed thereon. Two quantum boxes 6 form a basic cell 3. The boxes 6 are covered with an Si oxide film 4 of several tens of nanometers thick 3 and a second n-type polycrystalline Si conductive layer 5 is formed thereon. The first conductive layer is grounded through contacts from the back of the substrate, and second conductive layer is connected to a power voltage through contacts. Thus it is possible to inject electrons into the basic cell layer 3 with the substrate back grounded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum effect device composed of a quantum box, and more particularly to a novel storage device and a logic device with very low power consumption.

[0002]

2. Description of the Related Art Various devices using a quantum box have been proposed so far. In particular, recently, a cell in which electrons and holes can freely flow between a small number of quantum boxes by a tunnel effect has been proposed. Research has begun on coupled quantum boxes that contain a small number of electrons and holes as the minimum unit.

In particular, C.I. S. QC proposed by Lent and others
A (Quantum Cellular Automa)
ta) has attracted attention as an unprecedented breakthrough device. In brief, for example, a basic cell (basic four quantum box cell) composed of four quantum boxes as shown in FIG. 2 is considered. This basic cell is formed of a heterojunction system such as AlGaAs / GaAs, and the size of one quantum box in the cell is about the De Broglie length (20-30 nm). When only two electrons are put into this basic cell, the electrons recede from each other due to Coulomb repulsion, and a stable state with the lowest energy is obtained when each of them comes on a diagonal line. Here, since there are two diagonal lines, it is understood that there are two stable states in this basic cell. Considering the use of these two stable states (0, 1), this element can be used as a basic element of a current binary memory or logic circuit.

However, this basic cell has one major problem. That is, there is a problem of how to insert two electrons or holes into this basic cell. If one or three or more electrons or holes enter this basic cell, it is completely useless as a binary device.
nt himself also pointed out that the problem of how to put two electrons or holes in this basic cell has not yet been solved properly. Furthermore, the two electrons or holes entering the basic cell must now remain in the basic cell without a bias applied, but the problem has not yet been solved.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in consideration of the above-described problems. It is intended to provide an element.

[0006]

In order to achieve the above-mentioned object, the present invention uses two small quantum boxes capable of spatially confining carriers as a basic cell. Has a finite value, the quantum mechanical tunnel probability between the quantum boxes of carriers between the basic cells is sufficiently small to be negligible compared to the value in the cell, and the basic cell is not connected to the wiring or In a quantum effect device composed of a plurality of basic cells used as basic elements such as memory and logic circuits, electrodes are provided via a basic cell layer including a plurality of basic cells and an insulating layer or energy barrier layer with a certain thickness. The quantum effect device is characterized in that a conductive layer connected to the element is formed above or below the basic cell layer.

Further, the following quantum effect device is provided as a desirable embodiment of the present invention. That is, one conductive layer connected to an electrode through an insulating film or an energy barrier layer having a certain thickness is provided above and below the basic cell layer, and the thickness of the insulating layer or the height of the energy barrier layer is reduced. Different quantum effect devices are provided on the upper and lower sides.

That is, when a bias voltage is not applied to a conductive layer existing through an insulating layer or an energy barrier layer above and below the basic cell layer, or under normal operating conditions of the element, the basic cell layer and the conductive layer To provide a quantum effect element characterized in that no carrier moves between the quantum effect element and the quantum effect element.

Further, when a large bias voltage different from the normal operating condition of the device is applied between the conductive layers, the movement of carriers due to the tunnel effect between one conductive layer and the basic cell layer exists. However, there is provided a quantum effect element characterized in that no carrier moves between the other conductive layer and the basic cell layer.

Further, when the large bias voltage is released after the carrier is injected into the basic cell by the above method, the carrier injected into the quantum cell does not apply a bias voltage to the conductive layer, or the device operates under normal operating conditions. In the following, there is provided a quantum effect element which does not move to the conductive layer.

Further, the present invention provides a quantum effect device characterized in that only one carrier is injected into the basic cell when the carrier is injected from the conductive layer into the basic cell layer by the above method.
In addition, the device has another electrode capable of controlling one potential of the quantum box in the basic cell, and applies a voltage to the electrode when injecting carriers from the conductive layer into the basic cell to apply a voltage to the electrode. The quantum effect element is characterized in that the energy of one of the quantum boxes is increased so that only one carrier is allowed to enter a basic cell.

In the present invention, carriers are electrons or holes. When the carrier is an electron, the quantum box can be formed from a semiconductor or a metal, and when the carrier is a hole, the quantum box can be formed from a semiconductor. Further, the insulating layer or the energy barrier layer can be made of an insulator or a semiconductor, and the outer conductive layer can be made of a semiconductor or a metal. In addition, the semiconductor does not necessarily have to be a material having a bal 7 shape, and for example, a material such as polycrystal or fine particles can be used.

[0013]

FIG. 1 shows a first embodiment of a basic cell constituted by two quantum boxes according to the present invention. In this embodiment, an n-type Si layer 1 is formed as a first conductive layer, a Si oxide film 2 having a thickness of about several nm is formed thereon as an insulating film, and a plurality of quantum boxes 6 each having a side of several nm are formed thereon. And these quantum boxes are 2
The basic cell 3 is configured in units of units. The plurality of quantum boxes are covered with a Si oxide film 4 having a thickness of several tens nm,
An n-type polycrystalline Si5 as a second conductive layer is formed thereon. The first conductive layer is contacted and grounded from the back surface of the substrate, and the second conductive layer is also contacted and connected to the power supply voltage.

The method for producing the quantum effect device of this embodiment is as follows. On the surface of the n-type Si substrate 1, several n
After forming the m-th Si oxide film 2, amorphous Si having a thickness of several nm is formed by CVD. Next, the surface amorphous S
After recrystallizing the i-film by laser annealing,
After applying a resist and performing patterning by a normal developing process, other surface Si layers are removed by dry etching except for the quantum box region. Here, STM (S
scanning Probe Microscope)
And AFM (Atomic Force Microsc)
patterning of the quantum box may be performed by a local anodic oxidation method using a probe such as ope). However, in this case, the anodic oxide film can be used as it is as an energy barrier layer or a tunnel barrier layer, so that there is no need for etching. Next, a few tens of nm of Si oxide film 4 is deposited by CVD, and an n-type polysilicon layer 5 is further deposited thereon. Finally, the n-type polysilicon layer 5 on the back and front surfaces of the substrate 1
Contact each other. In this embodiment, electrons can be injected into the basic cell layer 3 by grounding the back surface of the substrate. Since the oxide film thickness on the surface side is sufficiently larger than the oxide film thickness on the substrate side, electrons can be injected into the basic cell layer from the substrate side. In this case, as shown in FIG. 3, when a voltage of several volts is applied with the electrode on the surface side being positive and electrons are injected from the substrate side into the quantum box of the basic cell layer by a tunnel effect, the state density of the basic cell, that is, Depending on the effective mass and size of the material used, it is possible to reliably inject only one electron per cell. What is important here is that the quantum box is very small, a few nanometers, and even if the second electron tries to enter the quantum box, injection is prohibited by the Coulomb blockade effect. Therefore, one electron can be injected into one cell. It is to become. The size of the quantum box is Si / SiO ₂
In a system, about 1 nm to 10 nm is desirable. In this case, 2
The energy required to enter the second electron is several tens to several hundreds of meV than the charging energy, and the second electron does not enter even at room temperature.
The state where only the electrons enter is maintained.

FIG. 4 shows a second embodiment of the present invention. Here, the difference from the first embodiment is that an electrode is attached to one of the quantum boxes of the basic cell. In the first embodiment, since the size of the quantum box could be made extremely small as several nm, one electron could be injected by a sufficient Coulomb blockade effect even in a basic cell having two quantum boxes. However, if the size of the quantum box cannot be made sufficiently small, giving at least one of the quantum boxes of the basic cell electrically high energy in advance makes it appear as if there is only one quantum box. Since the electron injection can be suppressed by the Coulomb blockade effect of one quantum box, the electron injection into the basic cell can be effectively performed.

In the above embodiment, the quantum box and S
i used an Si oxide film as an energy barrier layer,
For example, GaAs / Al as quantum box / energy barrier layer
GaAs, SiGe / Si, InP / AlInAsP,
A combination using a semiconductor heterojunction such as InGaAs / InP may be used, a metal such as Al or Au may be embedded in a Si oxide film as a quantum box, a silicon nitride film may be used as an insulating layer, and a conductive layer may be used. May be used as a metal. Further, the semiconductor or metal is not limited to bulk, and it is possible to use the polycrystalline body. Both the conductivity type and the p-type are good. Furthermore, the quantum effect element according to the present invention can be used as a basic element of a wiring, a memory, a logic circuit, or the like. As described above, the present invention can be variously modified and applied without departing from the gist thereof.

[0017]

As described above, according to the present invention, the basic cell is constituted by two quantum boxes, and a conductive layer is provided on at least one of the upper and lower sides of the basic cell layer via an insulating layer or an energy barrier layer. This makes it possible to provide an extremely stable, ultra-low power consumption quantum effect element in which only one electron is injected with high efficiency in the basic cell and the state is maintained even when the electron beam is left alone.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic cell according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a conventional quantum cellular automan device.

FIG. 3 is a band diagram for explaining electron injection into a basic cell according to the first embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a basic cell according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... n-type Si 1st conductive layer 2 ... Si oxide film 1st insulating layer 3 ... Basic cell layer 4 ... Si oxide film 2nd insulating layer 5 ... n-type polycrystalline Si 2nd conductive layer 6 ... Quantum box

Claims (2)

[Claims] 1. A basic cell comprising two small quantum boxes capable of spatially confining electrons or holes, in which quantum mechanical tunneling probability between electron or hole quantum boxes is finite. Between the basic cells, the quantum mechanical tunneling probability between the electron or hole quantum boxes is negligibly small compared to the value in the cell, and the basic cell is used for wiring, memory, logic circuit, etc. In a quantum effect device composed of a plurality of basic cells used as basic elements, a basic cell layer including a plurality of basic cells and a conductive layer connected to an electrode via an insulating layer or an energy barrier layer having a certain thickness are included. A quantum effect element formed above or below a basic cell layer. 2. A conductive layer connected to an electrode via an insulating layer or an energy barrier layer having a certain thickness is provided above and below the basic cell layer, and the thickness of the insulating layer or the energy barrier layer is 2. The quantum effect device according to claim 1, wherein the height is different between the upper side and the lower side.