JP3734290B2 - Quantum effect device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a quantum effect device, and more particularly to a quantum effect device having a memory function.
[0002]
[Prior art]
As memory capacity and miniaturization have increased, a new memory structure replacing the conventional DRAM has been required. As one of such memories, a memory using QCA (Quantum Cellular Automata) that operates in a region in which the number of electrons contributing to device operation is significantly reduced compared to a conventional DRAM has been proposed (CSLent et al., Quantum cellular automata; Nanotechnology, vol. 4, p49-57).
[0003]
FIG. 12 shows a cell structure of a memory using such a quantum effect. The cell 2 is composed of four (or five) quantum dots 1, and two electrons are injected into the cell. When two electrons are injected into the cell in this way, the electron distribution is present in the two quantum dots aligned on the diagonal line by the Coulomb force according to the electric field from the outside (quantums indicated by hatching in the figure). There are two electrons one by one in the dot). At this time, there are two states, that is, electrons exist in the right oblique quantum dots and electrons exist in the left oblique quantum dots . The two states of this constitutes a memory circuit by defining a 0,1.
[0004]
Such a memory is suitable for miniaturization and high integration due to features such as the premise of operation in a region with few electrons and a simple cell configuration, and is expected as a quantum effect memory device replacing the DRAM. It is increasing.
[0005]
[Problems to be solved by the invention]
However, the memory using the quantum effect proposed by Lent et al. Has the following problems, and has not yet provided a quantum effect device that actually operates at room temperature. That is, (1) The energy difference between the ground state and the excited state that determines 0 and 1 is less than 1 meV (size that can be processed by the current lithography technology), and the state of 0 and 1 cannot be kept stable with this energy difference. There is a problem that the room temperature operation of the element cannot be realized.
(2) Also, in order to operate at room temperature, the cell size and quantum dot type must be in atomic order, which makes the apparatus large, and there are major problems in manufacturing methods such as mask etching suitable for mass production cannot be applied. Has a point.
(3) As described above, since the energy difference between the ground state and the excited state is small, α-rays generated from U and Th contained in the package material, high-energy electron beams and X-rays used in the process, or There is a problem that a so-called soft error occurs due to electrons, holes, etc. generated by a high electric field generated inside the device.
[0006]
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a quantum effect device that solves the above problems and operates stably without being affected by thermal fluctuations and electrical fluctuations.
It is another object of the present invention to provide a memory in which information does not volatilize without being biased at all times.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a quantum effect device according to the present invention is provided with a first layer having a cell unit having at least four or more charge confining regions, and separated from the first layer. A second layer having a high concentration of charge, wherein a plurality of carriers exist in the cell unit, and the plurality of carriers move between the four or more charge confining regions in the cell unit. The resulting difference in polarization state of the plurality of carriers is defined as 0, 1, and the second layer induces charges having signs opposite to those charges corresponding to the charges of the plurality of carriers. It is characterized by that.
[0008]
The quantum effect device according to the present invention is characterized in that the second layer is a metal layer or a semiconductor layer in which a high concentration of charge exists.
In the quantum effect device according to the present invention, the charge confining region is formed of a first semiconductor, and the first semiconductor layer and the second layer are formed by a second semiconductor having a larger band gap than the semiconductor, or a first insulator. The layers are separated from each other.
[0009]
Further, the quantum effect device according to the present invention is formed on the third semiconductor or the second insulator having a large band gap formed on the first layer and the third semiconductor or the second insulator. A bit line and a word line.
[0010]
In addition, the quantum effect device according to the present invention includes the charge confinement region and a band structure surrounding the region so that there are two carriers in the cell unit, and the third or more carriers do not enter the cell. It is characterized by having.
[0011]
[Action]
When there is a point charge on a layer (image charge layer) where a high-concentration charge such as metal or two-dimensional electron gas exists, the point charge having the opposite sign to the point charge in the image charge layer The charge in the image charge layer is rearranged so that there is. This is a phenomenon observed in a substance (image charge layer) in which a sufficient number of electrons are present to screen a local electrical gradient, where the electric lines of force of the point charge enter the interface of the image charge layer, This occurs by arranging a large number of electrons in the image charge layer so as to be perpendicular to the interface.
[0012]
According to the present invention, a plurality of charges are confined in a unit cell so as to form a polarization state, and this cell is disposed close to the image charge layer, thereby rearranging the point charges in the cell. The point charge having the opposite sign in the image charge layer is strongly coupled to realize an extremely stable polarization state.
[0013]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1A shows a memory using the quantum effect according to the first embodiment of the present invention. In this embodiment, the cell 2 forming the memory is composed of four quantum dot cells, and a metal layer is used as the image charge layer 4 for stabilizing the bistable state. The cell 2 and the image charge layer 4 are insulated by an insulating layer 3.
[0014]
The manufacturing method of a present Example is demonstrated below.
On the GaAs substrate 5, a metal layer 4 made of Mo is laminated by 500 angstroms (hereinafter referred to as A) by sputtering, vapor deposition or the like. Next, 200A of SiO2 film is laminated as the insulating layer 3 by the CVD method. Four quantum dot cells made of GaAs / AlGaAs are formed on the SiO2 insulating layer 3.
[0015]
At this time, there is a large carrier supply layer called the metal layer 4, and electrons are supplied from the metal layer 4 into the cell 2 so as to be polarized by controlling the size of the quantum dots and the film thickness of the insulating layer 3.
[0016]
Meanwhile, the quantum dot in each cell energy level is required to be one. The nth energy level of the quantum dot is determined by the size L of the quantum dot. The energy level at this time can be roughly expressed by the following equation.
[0017]
En = (h / 2π) ² π ² n ² / (2 mL ² ) (1)
By reducing the size of the quantum dots, the energy level interval in the quantum dots can be increased. At this time, the energy discontinuity (energy difference) of the conduction band of the semiconductor inside and outside the quantum dot is designed so that the second energy level in the quantum dot is larger than this energy discontinuity. Just keep it. By designing in this way, two electrons can be supplied to the quantum dot diameter from the metal layer 4 via the insulator 3, and no more electrons can enter the cell because of the high energy level.
[0018]
Further, by configuring as described above, a polarization state is caused in the cell 2, and an image charge corresponding to the charge in the cell is generated in the metal layer 4, so that the polarization state of the cell is stabilized. FIG. 2 shows how an image charge (positive charge in this case) corresponding to the charge in the cell (negative charge in this case) is induced in the metal layer.
[0019]
FIG. 3 schematically shows how the eigenvalues that characterize the two stable states of the memory thus formed are changed. As shown in the figure, the energy state of the electrons confined in the quantum dot shows a jump value due to the quantum effect, and the energy difference between the ground state and the excited state is about 50 meV when the diameter of the quantum dot is about 500 A. Thus, when this is converted into temperature, it becomes room temperature or higher, indicating that room temperature operation can be easily performed.
[0020]
On the other hand, although not shown in the figure, in the quantum effect memory suggested by Lent et al., The energy difference between the ground state and the excited state is only 0.5 meV, which is 5K in terms of temperature, and cannot operate at room temperature.
[0021]
As described above, according to the present invention, a cell portion that performs a memory operation is a layer having a charge that is high enough to cause an image charge phenomenon, such as a metal or a highly doped semiconductor through an insulating layer or the like. By forming the structure, an extremely stable polarization state can be created, and a quantum effect memory capable of operating at room temperature can be created.
[0022]
FIG. 4 is a sectional view of a memory using the quantum effect according to the second embodiment of the present invention.
In this embodiment, the two-dimensional electron gas layer 8 supplied with electrons from the uniform doping layer 6 is used as an image charge layer, and quantum dots are formed on the two-dimensional electron gas layer 8 via a semiconductor 9 having a large band gap. The system 10 is formed.
[0023]
A method for creating the memory device according to this embodiment will be described below.
On a substrate 6 made of n-type AlGaAs or n-type InP or the like, an MBE method is used to form an i-type AlGaAs spacer layer 7, an image charge layer 8 made of i-type GaAs or i-type InGaAs, and an i-type AlGaAs semiconductor layer 9 (band gap). A large semiconductor layer) and GaAs.
[0024]
Next, the quantum dots 10 are formed by patterning the GaAs layer stacked on the uppermost layer using photolithography. Further, the memory device of the present invention can be formed by laminating the AlGaAs semiconductor layer 11 on this substrate using the MBE method.
[0025]
At this time, the combination of the quantum dot 10 / semiconductor layer 11 in the cell includes InGaAs / AlInAs, InGaAs / InP, InGaAs / GaInSb, etc. in addition to GaAs / AlGaAs.
[0026]
FIG. 5 is a sectional view of a memory using the quantum effect according to the third embodiment of the present invention.
In this embodiment, the two-dimensional electron gas layer 8 supplied with electrons from the planar doping layer 13 is used as an image charge layer, and the quantum dot system 10 is formed on the two-dimensional electron gas layer 8 via a semiconductor 9 having a large band gap. Is formed.
A method for creating the memory device according to this embodiment will be described below.
[0027]
A planar doped layer 13 is formed by planarly doping Si on the surface of the substrate 6 made of i-type AlGaAs. Next, an i-type AlGaAs spacer layer 7, an image charge layer 8 made of i-type InGaAs, and an i-type AlGaAs semiconductor layer 9 (semiconductor layer having a large band gap) are formed on the substrate 12 on which the planar doped layer 13 is formed using the MBE method. ), And GaAs.
[0028]
Next, the quantum dots 10 are formed by patterning the GaAs layer stacked on the uppermost layer using photolithography. Further, the memory device of the present invention can be formed by laminating the AlGaAs semiconductor layer 11 on this substrate using the MBE method.
[0029]
At this time, the combination of the quantum dot 10 / semiconductor layer 11 in the cell includes InGaAs / AlInAs, InGaAs / InP, InGaAs / GaInSb, etc. in addition to GaAs / AlGaAs.
[0030]
FIG. 6 is a sectional view of a memory using a quantum effect according to the fourth embodiment of the present invention.
In this embodiment, an n ⁺ layer 14 is used as an image charge layer, and a quantum well 10 is formed on the n ⁺ layer 14 via an insulating layer 9.
[0031]
A method for creating the memory device according to this embodiment will be described below.
On the n + -type GaAs semiconductor substrate 6, i-type AlGaAs 9 (semiconductor with a large band gap) is laminated using MBE, and further GaAs is laminated.
[0032]
Next, the quantum dots 10 are formed by patterning the GaAs layer stacked on the uppermost layer using photolithography. Further, the memory device of the present invention can be formed by laminating the AlGaAs semiconductor layer 11 on this substrate using the MBE method.
[0033]
In this embodiment, n ⁺ GaAs 14 functions as an image charge layer. Further, an n ⁺ Si layer can be used as the image charge layer 14 and 9 can be a SiO ₂ layer. Further, the p ⁺ layer may be used as an image charge layer instead of the n ⁺ layer.
[0034]
At this time, the combination of the quantum dot 10 / semiconductor layer 11 in the cell includes InGaAs / AlInAs, InGaAs / InP, InGaAs / GaInSb, etc. in addition to GaAs / AlGaAs.
[0035]
FIG. 7 shows a band diagram when both the cells constituting the quantum dots and the image charge layer are made of semiconductors. FIG. 8 shows a band diagram when the cell constituting the quantum dot is made of a semiconductor and the image charge layer is made of metal.
[0036]
In this case, when the cell is formed of a semiconductor, a semiconductor having a small band gap is used for the quantum dot portion, and the surrounding portion can be formed of a semiconductor having a larger band gap than the semiconductor of the quantum dot. For example, GaAs can be used for the quantum dots, and GaAlAs can be used for the surrounding portions. Further, the isolation between the cell and other cells can be made of a semiconductor having a higher band gap or an insulating layer.
[0037]
Examples of combinations of quantum dots in one cell and surrounding material systems include InGaAs / AlGaAs, SiGe / Si, InPb / InAs, Si / SiO ₂ , and Al / Al ₂ O ₃ , It can also be used for an interface material system that generates a two-dimensional gas as an image charge layer.
[0038]
Examples of the metal serving as the image charge layer include W, CaF, TiN, Al, Au, and Pt. Substance used as this time image charge layer, screening length due to the charge, for example in Thomas-Fermi approximation, can the electron concentration n, and the Fermi energy was EF, given by (6πe2n / EF) ^1/2, It is only necessary that the length of the material system be larger than the size of the region confining the charge in the cell.
[0039]
In addition, the quantum dot diameter is limited by the screening length of the material system of the image charge layer, and these relations are such that the quantum dot diameter> the screening length, so that the quantum dot diameter in the region where charges accumulate in the quantum dot system. The mirror image can be clearly displayed on the image charge layer. That is, by making the screening length sufficiently short, the charges in the image charge layer can move easily. The screening length of 10 ¹⁸ / cm ³ GaAs is 10 angstroms.
[0040]
FIG. 9 is a perspective view of a memory using the quantum effect according to the fifth embodiment of the present invention. In this embodiment, a plurality of cells are grounded at intervals equal to the cell size, and word lines and bit lines are arranged to integrate the memory.
[0041]
A metal layer 4 that is an image charge layer is formed on a substrate 5, and a plurality of memory cells are formed on the metal layer 4 via an insulating layer 3. Further, two adjacent quantum dots in the memory cell are provided with a bit line 7 and a word line 6 formed by Al lines.
[0042]
FIG. 11 shows an enlarged view of this quantum dot, bit line 7 and word line 6. The bit line 7 and the word line 6 are formed via a highly doped semiconductor 16 (for example, n ⁺ Si) and the interlayer insulating film 15 and serve as electrodes for transmitting information to or reading information from the in-cell dots.
[0043]
The electrodes forming the bit line 7 and the word line 6 and the dot in the cell are close to each other through the interlayer insulating layer 16, but these electrodes have a role of giving an electric field effect in the cell, It is not directly connected to the cell.
[0044]
In addition, although highly doped semiconductors are attached to these electrodes, by doing so, it is possible to avoid the direct influence of the current flowing through the word lines and bit lines in the quantum cells.
[0045]
FIG. 10 is a circuit diagram showing the relationship between bit lines and word line memory cells. Although the present invention has been described with respect to four quantum dot cells including four quantum dots in one cell, the present invention is not limited to four quantum dots, and can be realized in cells including five quantum dots or quantum dots of six or more quantum dots. It is.
[0046]
In addition, the number of electrons confined in one cell is not limited to two, and may be two or more. This is because a very stable ground state can be realized by generating a polarization state by image charge as in the present invention.
[0047]
【The invention's effect】
As described above, in the present invention, image dots having a sign opposite to that in the quantum dots are induced by forming quantum dots at intervals on the high-concentration charge layer, and the Coulomb mutual relationship between these charges is induced. As a result of strong electrical coupling caused by the action, it is possible to realize an extremely stable polarization state that is resistant to thermal fluctuations and electrical fluctuations at room temperature.
[Brief description of the drawings]
FIG. 1 is a perspective view of a quantum effect device according to a first embodiment of the present invention. FIG. 2 is a diagram showing electric lines of force generated between an image charge induced in an image charge layer and an original charge. FIG. 4 is a cross-sectional view of the quantum effect device according to the second embodiment of the present invention. FIG. 5 is a diagram according to the third embodiment of the present invention. FIG. 6 is a sectional view of a quantum effect device according to a fourth embodiment of the present invention. FIG. 7 is a band diagram of a quantum dot and an image charge layer of the quantum effect device of the present invention. FIG. 8 is a band diagram of a quantum dot and an image charge layer of the quantum effect device of the present invention. FIG. 9 is a perspective view of a device in which a memory device using the quantum effect of the present invention is integrated. [10] The memory device using the quantum effect of the present invention FIG. 11 is a sectional view of a memory device using the quantum effect of the present invention. FIG. 12 is a diagram of a conventional quantum effect device.
DESCRIPTION OF SYMBOLS 1 ... Quantum dot 2 ... Cell 3 ... Insulator 4 ... Image charge layer 5 ... Substrate 6 ... Uniform modulation
DESCRIPTION OF SYMBOLS 7 ... Insulating layer 8 ... Two-dimensional electronic layer 9 ... Semiconductor layer 10 with a large band gap ... Quantum dot 11 ... Insulating layer 12 ... Substrate 13 ... Planar dope layer 14 ... n ⁺ semiconductor layer 15 ... Interlayer insulating film 16 ... High concentration semiconductor layer

Claims (5)

A first layer having a cell unit having at least four charge confining regions, and a second layer having a high concentration of charges provided separately from the first layer, A plurality of carriers exist in a cell unit, and the difference in polarization state of the plurality of carriers caused by the movement of the plurality of carriers between the four or more charge confinement regions in the cell unit is 0, 1 The quantum effect device is characterized in that a charge having a sign opposite to that of the plurality of carriers is induced in the second layer corresponding to the charges of the plurality of carriers .   2. The quantum effect device according to claim 1, wherein the second layer is a metal layer or a semiconductor layer having a high concentration of charge.   The charge confinement region is made of a first semiconductor, and the first layer and the second layer are separated from each other by a second semiconductor having a larger band gap than the semiconductor, or by a first insulator. 3. The quantum effect device according to claim 1, wherein the quantum effect device is characterized in that:   A third semiconductor or second insulator having a large band gap formed on the first layer; and a bit line and a word line formed on the third semiconductor or second insulator. The quantum effect device according to claim 1, wherein the quantum effect device is provided.   2. The charge confinement region and a band structure surrounding the region are provided so that there are two carriers in the cell unit, and the third or more carriers do not enter the cell. The quantum effect device according to claim 1, claim 2, claim 3 or claim 4.

Images