JP3311033B2 - One-electron tunneling element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-electron tunneling device formed by connecting a plurality of ultrafine tunnel junctions in series.

[0002]

2. Description of the Related Art When one electron tunnels with a single tunnel junction (junction capacitance: C, junction resistance: R), ΔE = e ² before and after the tunnel. A change in electrostatic energy of about / 2C is a problem. ΔE can be greater than the thermal energy in an ultrafine tunnel junction where the junction capacitance C is very small. Depending on the charge amount of the tunnel junction, tunneling of electrons causes such an increase in energy, so that even tunneling of one electron is prohibited. This is the Coulomb blockage
Blockade) (KKLikharev, IBM J. Res. Devel
op., 32, 144 (1988)). Therefore, although the tunnel phenomenon is originally due to the wave nature of the electrons, in the device using the ultrafine tunnel junction, the electrons are tunneled one by one in particles.

A one-electron tunneling device utilizing the electron behavior of such an ultrafine tunnel junction is expected to be a device having a simple structure and suitable for miniaturization and high integration.

In order to clearly show Coulomb blockade in an ultrafine tunnel junction, ΔE needs to be larger than any of thermal and quantum mechanical fluctuations (see the above-mentioned literature). That is, assuming that the Boltzmann constant is k _B , the Planck constant is h, and the absolute temperature is T, it is necessary to satisfy the condition that ΔE is sufficiently larger than k _B T and ΔE is sufficiently larger than h / 2πRC. Furthermore, in a device having one tunnel junction, stable Coulomb blockade cannot be expected due to excitation of the electromagnetic mode of the entire circuit, and a multiple tunnel junction structure (tunnel element column structure) in which a plurality of tunnel junctions are connected in series is effective. It is known that (YVNaza
rov, Zh. Eksp. Teor. Fiz., 96, 975 (1989)).

A one-electron tunneling element has a junction capacitance C
In the case of the aF order, there is a possibility of operating at room temperature. Only
However, in such ultra-fine and highly integrated devices, there are various reasons.
Somewhat low temperature operation is required. In such cases, t
The basic element size of the tunneling element is the inelastic scattering of electrons.
Phase interference length L determined by_F= (Dτ_in)^1/2 (This is T^-p(P = 1 ~ 2)
And the thermal diffusion length L, which is a measure of blurring due to heat._T= (1/2) (hD / k_BT)^1/2  May be smaller (P.A. Lee et al., Phys.
v.B 35, 1039 (1987)). Where D, τ_inIs it
These are the electron diffusion constant and the inelastic scattering time, respectively.

However, the quantum effect due to impurity scattering changes the electronic state of the lead wire / electrode, and has a great effect on Coulomb blockage. The electron conduction characteristics of the lead wire / electrode fluctuate randomly, and the characteristics of the tunnel junction device utilizing Coulomb blockage also fluctuate randomly. Therefore, various one-electron tunneling devices (KKLikh
arev, IBM J. Res. Develop., 32, 144 (1988)) fluctuates and does not function properly.

[0007]

As described above, the conventionally proposed one-electron tunneling device has a problem that fluctuations in the conduction characteristics of the lead wires and electrodes hinder normal operation of the device.

The present invention has been made in view of the above circumstances, and has as its object to improve the characteristics by reducing the effects of quantum fluctuations and external circuits generated in functional basic units. An object of the present invention is to provide an electron tunneling device.

[0009]

According to the present invention, there is provided a tunnel element array in which a plurality of ultrafine tunnel junctions in which the charge energy of one electron is larger than the thermal energy at an operating temperature are connected in series. In a one-electron tunneling element provided with a charge modulating section and a pair of signal extracting sections sandwiching the charge modulating section, a series connection direction of a tunnel junction in each of the charge modulating section and the pair of signal extracting sections is provided.
And wherein the orthogonal directions of the length, and the length of the tunnel element row of the range sandwiched between a pair of signal extraction portion is set longer than any of the inelastic scattering length and thermal diffusion length of electrons and I do.

In the present invention, more preferably, the region between the pair of signal extraction portions of the tunnel element array includes two or more tunnel junctions, and the power supply terminals at both ends of the tunnel element array and each signal extraction section. At least one or more tunnel junctions are included between them.

[0011]

[Function] In a single tunneling element whose main element is an ultrafine tunnel junction in which the charging energy of one electron is larger than the thermal energy at the operating temperature, stable Coulomb blockage can be expected by exciting the electromagnetic mode of the entire circuit. Therefore, a one-electron tunneling element having a structure in which tunnel elements are connected in series is effective. On the other hand, since the phase information of the electronic wave, to be stored over a phase interference L _F or thermal diffusion length L _T inelastic scattering length of such electron scattering,
In smaller systems than L _F and L _T, various quantum effects due to phase interference effect becomes obvious. In particular, when the size of the conduction characteristic measurement direction of the conductor is larger than the elastic scattering distance (mean free path) 1 due to impurities, it reflects that electrons are randomly scattered by impurities and the phase of the wave function is randomly changed. As a result, the conductance of the conductor fluctuates. Since this fluctuation reflects the microscopic spatial arrangement of impurities, the fluctuation is different even in a conductor similarly prepared and cannot be used as a basic element having the same characteristics.

Therefore, in a one-electron tunneling element,
Are also basic elements such as multiple tunnel junctions, charge modulation sections,
Each of the signal extraction sections is larger than the phase interference length.
It is necessary to do. That is, L is their length,
L_C = Max ｛L_F, L_Tよ う so that it is bigger than
Design basic elements. So the fluctuations are average
And the fluctuation of the conduction characteristics is (L_C/ L)^{(4-d) / 4}  (P.A. Lee et al., Phys. Rev. B 35, 1039)
 (1987)). Here, d is the dimension of the electronic system.

Further, an external power supply terminal section such as a constant current source and a constant voltage source and a tunnel element row, a signal extraction section such as a potential difference,
In relation to the basic functional element called the charge modulation section,
By including two or more tunnel junctions between a pair of signal extraction parts and inserting at least one or more tunnel junctions between a power supply terminal part and a signal extraction part, an influence on element characteristics of an external circuit is obtained. Can be greatly reduced.

By constructing a basic unit of the element function by the basic elements having the above conditions, a one-electron tunneling element having stable characteristics and a composite one-electron tunneling element using the same as a basic unit are constructed. Things become possible.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to embodiments.

FIG. 1 is a plan view of one electron tunneling element according to one embodiment of the present invention. Basic element is lead wire electrode 2.
And an ultrafine tunnel element composed of a tunnel junction 1 provided between the adjacent lead wire electrodes 2, and a plurality of these are connected in series to form a tunnel element row. A pair of signals (potential difference)
The extraction portions 5 and 6 are drawn out from the center electrode 2 in a continuous state. A charge modulation section 7 for controlling the charge state of the tunnel junction 1 from outside by capacitive coupling is provided between the signal extraction sections 5 and 6. Power supply terminals 3 and 4 are provided at both ends of the tunnel element row. In this embodiment, two tunnel junctions 1 are provided between one power supply terminal 3 and the signal extraction unit 4 and between the other power supply terminal 4 and the signal extraction unit 6, respectively.

An external power supply 8 is connected between the power supply terminals 3 and 4 at both ends of the element. The external power supply 8 may be either a voltage source or a current source. The modulation voltage source 9 is also connected to the charge modulation section 7.

FIG. 2 shows an example of the main structure of FIG. Adjacent ones of the lead wires 2 of the tunnel junction are arranged so as to partially overlap each other, and the tunnel junction 1 is configured with a tunnel insulating film interposed between the overlapping portions.
The lead electrode 2 has, for example, a line width of 0.05 μm and a thickness of 0.5 μm.
The tunnel oxide film is an Al oxide having a thickness of 3 nm. The junction area of the tunnel junction 1 is, for example, 0.05 × 0.01 μm ² ). The charge modulation section electrode 7 is laminated on the lead wire electrode 2 via the insulating film 11.

In the device configuration shown in FIG. 1, the size of each part is as follows. The length L _A of the signal extraction units 5 and 6,
Both L _B and the length L _G of the charge modulation section 7 are equal to 0.
2 μm, the distance L _AB between the signal extraction units 5 and 6 is 0.37
μm. These are larger than the phase interference length L _C (= 0.04 μm) at the operating temperature of 15K.

In the embodiment, the number of tunnel junctions between the signal extraction units 5 and 6 is set to thirteen, which is L _AB > L
_It suffices if there are two or more in the range satisfying _C. In the embodiment, two tunnel junctions are provided between the signal extraction units 5 and 6 and the power supply terminal units 3 and 4, respectively. At least one tunnel junction may be provided.

FIGS. 3 (a) and 3 (b) show the potential difference V between a pair of signal output portions of the devices of the comparative example and the embodiment according to the change of the potential U of the charge modulation portion during the constant current operation. Fig. 3 (a)
In the comparative example, the length L _AB of the element row between the signal extraction units is set to L _C
FIG. 3B shows the case of the embodiment. In the comparative example, the fluctuation that differs for each tunnel element appears in the periodic fluctuation of the potential difference, whereas in the present embodiment, such fluctuation is suppressed and a beautiful periodic fluctuation is obtained.

The present invention is not limited to the above embodiment. For example, in the embodiment, the tunnel junction is formed of a metal and a metal oxide, but a semiconductor such as silicon may be used instead of the metal, and a silicon oxide film or the like can be used as the tunnel insulating film. That is, a tunnel element row can be formed by the MOS transistor structure. The tunnel junction can also be formed using a so-called point contact pinch-off state in which a part of the channel of a silicon oxide or silicon MOS transistor is locally narrowed to about the wavelength of electrons. In addition, the present invention can be variously modified and implemented without departing from the spirit thereof.

[0023]

As described above, according to the present invention, each element of the basic unit on the element function of a one-electron tunneling element using an ultrafine tunnel junction is selected so as not to be affected by an external circuit. And excellent device characteristics with little fluctuation can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a one-electron tunneling device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a main part structure of the embodiment.

FIG. 3 is a view showing element characteristics of the example together with a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tunnel junction part, 2 ... Lead wire electrode, 3, 4 ... Power terminal part, 5, 6 ... Signal extraction part, 7 ... Charge modulation part, 8 ... Constant current source, 10 ... Tunnel insulating film, 11 ... Insulating film .

Claims (2)

(57) [Claims] 1. A tunnel element array in which a plurality of ultra-fine tunnel junctions in which the charge energy of one electron is larger than the thermal energy at an operating temperature is connected in series. In a one-electron tunneling element provided with a pair of signal extraction units with a modulation unit interposed therebetween, each of the charge modulation unit and the pair of signal extraction units is provided.
In the direction perpendicular to the series connection direction of the tunnel junction
It is, and single-electron tunneling device, characterized in that the length of the tunnel element row of the range sandwiched between a pair of signal extraction portion is set longer than any of the inelastic scattering length and thermal diffusion length of the electrons. 2. The semiconductor device according to claim 1, wherein the tunnel element array includes two or more tunnel junctions in a region between the pair of signal extraction portions,
2. The one-electron tunneling device according to claim 1, wherein at least one or more tunnel junctions are provided between the power supply terminal portions at both ends of the tunnel device row and each signal extraction portion.