JP2533134B2 - Particulate transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] Regarding a novel structure of a transistor utilizing a tunnel effect, a tunnelable distance between island-shaped particles and a source electrode and a drain electrode is widened to facilitate fabrication. In order to achieve the above, an island-shaped fine particle is provided between the source electrode and the drain electrode, and a tunnel current flows between the source electrode and the drain electrode through the fine particle, and the tunnel current flows to the fine particle. In a transistor controlled by a voltage applied to a gate electrode coupled by capacitance, the fine particles are composed of a conductive material and a first semiconductor layer, and a second portion is provided between the fine particles and a source electrode and a drain electrode. The barrier height for traveling carriers is
Is determined by the band discontinuity at the interface between the semiconductor layer and the second semiconductor layer.

[Field of Industrial Application] The present invention relates to a novel structure of a particle transistor, that is, a transistor utilizing a tunnel effect.

Transistors are basic elements of electronic calculators and other electronic equipment, and their speeding up and power consumption reduction are essential for performance improvement, and miniaturization, speeding up, and power consumption reduction due to improvements in currently used transistors. Is planned,
There is a limit to this, and accordingly, the advent of new transistors is desired.

[Conventional technology]

For example, if the MOSFET is miniaturized, the short channel effect appears and there is a limit to the shortening of the channel, and if these elements (transistors) are highly integrated, high-speed operation is possible due to the load capacitance due to the increase in wiring capacitance and fanout. It is damaged, and for that reason, an element having a large Gm (transmission conductance) is required, but there is a limit to that.

Therefore, the inventor has proposed a new structure utilizing the tunnel effect as a high speed, high Gm, low power consumption transistor (see Japanese Patent Application No. 62-054844). FIG. 5 is a principle diagram thereof, FIG. 5 (a) is a structural schematic diagram, and FIG. 5 (b) is an equivalent circuit diagram, in which 1 is conductive fine particles, 2 is a source electrode, and 3 is a drain electrode. , 4 are gate electrodes, Cs, Cd, Cg are capacitances between the fine particles 1 and each source, drain, gate electrode, and Gs, Gd are tunnel conductances between the fine particles and each source, drain electrode. Thus, the fine particles 1 and the surroundings are insulated, the fine particles 1 and the gate electrode 4 are coupled by the electrostatic capacitance Cg, the fine particles and the source / drain electrodes are coupled by the tunnel conductances Gs, Gd, and the capacitance is Cs, Cd
It has Then, the fine particles 1 are made minute and the total capacity C = Cs + Cd + Cg is made extremely small.

Here, the reason why the fine particles 1 are made minute and the total capacitance C is made small will be explained. To add the charge Q to the capacitance C, E =
Energy of Q ² / 2C is required, and therefore the above-mentioned fine particles 1
Energy (e; absolute value of electronic charge) of e ² / 2C is required for one electron (carrier) to enter and exit. However, when the capacitance C is large and Ec = e ² / 2C is small, the thermal energy kT works (k; Boltzmann's constant, T; absolute temperature). Therefore, when the capacitance C is small and Ec is large, Ec> kT. , Thermal exchange of electrons becomes impossible. Under the condition of Ec> kT, when a voltage is applied to the gate electrode 4 which is coupled to the fine particles 1 by the electrostatic capacitance Cg, the potential of the fine particles 1 changes, and the source electrode 2 changes the fine particles 1 to the drain electrode. Three
The electrons can be moved from the particles to the particles 1 by the tunnel effect, and a tunnel current can be passed. In this way, by controlling the voltage applied to the gate electrode, a transistor operation similar to that of a FET is performed, and in order to obtain this transistor operation, the fine particles are made fine to reduce the total capacitance C. is there.

Fig. 6 shows the Id-Vd characteristic diagram of the transistor, where Cs / Cg = Cd / Cg = 0.1 and Ec / kT = 30, and the gate voltage V
It is a characteristic value in which g is changed from 0.4 × (e / Cg) to 0.58 × (e / Cg). Here, since Ec = e ² / 2C has a value of several meV, T becomes an extremely low temperature of about 4.2K. The drain current Id on the vertical axis and the drain current Vd on the horizontal axis are shown as normalized values.

7 (a) and 7 (b) show a conventional embodiment of this transistor. FIG. 7 (a) is a plan view and FIG. 7 (b).
FIG. 7A is a sectional view taken along line AA ′ of FIG. Semi-insulating InP substrate 5
Particles 1 made of platinum (Pt; thickness 50 Å, diameter 50 Å) on the surface of the, and source electrode 2 and drain electrode 3 made of platinum (thickness 200 Å) on both sides of them, the distance between the particles 1 and each electrode 2, 3 Are both 500 Å, and the SiO ₂ film (thickness 3
An insulating film 6 made of 00Å) is provided, and a gate electrode 4 (thickness 1000Å) also made of platinum is provided on the insulating film. A plurality of fine particles 1 may be provided between the source electrode and the drain electrode.

In practice, the maximum size of the fine particles 1 should be limited to approximately 3000 Å or less to reduce the capacitance C so that Ec> kT. For example, if spherical fine particles with a diameter of 1000 Å exist in isolation. , Its capacitance C is represented by C = 4πεa (ε; permittivity, a; radius of sphere), and if there is an electrode in the vicinity as in this structure, the capacitance becomes about twice, and as a result, Ec becomes It is thought to be about 1 meV. On the other hand, the temperature T of liquid helium (He) is 4.2 ° k, and its thermal energy kT is 0.36 meV, so that the relation of Ec = e ² / 2C> kT is established. Further, since the liquid helium is lowered by the pump suction to the temperature T = 2 ° k, the maximum size of the fine particles is about 3000Å.

[Problems to be solved by the invention]

However, the most important point in the above-mentioned transistor is the distance between the electrode and the fine particles that can be tunneled. The wider the tunnel distance (tunnel length), the easier the fabrication of the transistor. Moreover, the tunnel length increases in inverse proportion to the 1/2 height of the tunnel barrier height ΦB. (D; tunnel length)), and therefore it is only necessary to realize a low tunnel barrier.

In the example using the above InP substrate, it is possible to reduce the height of the barrier by selecting a conductive material of fine particles under specific conditions, but in general, the height of the barrier is relatively high, therefore, For example, in the case of GaAs, dozens of Å
Only tunnel distances (several nm) are allowed.

The present invention proposes a transistor aiming at facilitating the manufacture by widening the tunnelable distance.

[Means for solving problems]

The purpose thereof is that the fine particles are composed of a conductive material and a first semiconductor layer, and the fine particles are connected to the source electrode and the drain electrode by a second semiconductor layer, so that the height of the barrier against traveling carriers is increased. This is achieved by a particle transistor defined by band discontinuity at the interface between the first semiconductor layer and the second semiconductor layer.

[Work]

That is, the particle transistor according to the present invention forms a low barrier by utilizing the discontinuity of the band structure generated at the hetero interface of the semiconductor layer, and tunnels the low barrier. Then, the tunnel length can be widened, and such a heterojunction of the semiconductor layers can be formed with good controllability, which facilitates the production of the transistor element.

〔Example〕

Hereinafter, embodiments will be described in detail with reference to the drawings.

1 (a) and 1 (b) show an embodiment (I) of a transistor according to the present invention. FIG. 1 (a) is a plan view,
FIG. 3B is a sectional view taken along line BB ′ of FIG. 11 in the figure
Is gold (thickness 50 Å; conductive material) that constitutes fine particles, 12 is a source electrode, 13 is a drain electrode, 14 is a gate electrode made of aluminum, 15 is a semi-insulating GaAs substrate, 16 is a SiO ₂ film (thickness
500Å), 17 is Al _0.05 Ga _0.95 As layer (thickness 1000Å), 18,18 '
Is an undoped GaAs layer (thickness 50 Å) and 19, 19 'is an n ⁺ -GaAs layer (thickness 50 Å). And the fine particles are undoped GaAs layer
18, n ⁺ -GaAs layer 19 (first semiconductor layer) and gold 11 are used. The source is an undoped GaAs layer 18 ', n ⁺ -GaAs layer 19'.
And source electrode 12 and the drain is undoped GaAs
Layer 18 ', n ⁺ -GaAs layer 19' and drain electrode
The lGaAs layer 17 is a second semiconductor layer in which fine particles are coupled to the source electrode and fine particles are coupled to the drain electrode. It should be noted that the terms source and drain mean source electrode and drain electrode in a broad sense, and include undoped GaAs layer 18 'and n ⁺ -GaAs layer 19' of ohmic contact, which are described in the claims. The source electrode and the drain electrode have a broad meaning.

FIG. 2 is an energy band diagram for explaining the tunnel operation seen in Example (I), where EF is the Fermi level and Ec is the lower limit of the conduction band. The X value of the Al x Ga _1- x As layer 17 as the second semiconductor layer is set to 0.05 to form a crystal very close to a GaAs crystal for heterojunction, so that a low barrier is formed. In addition, since the n ⁺ -GaAs layers 19 and 19 'which are in ohmic contact with the particles, the source electrode and the drain electrode contain many impurities and degenerate, the conduction band Ec has an energy lower than the Fermi level EF. Occupy a level. Therefore, the electron tunnels through the heterojunction with a low barrier, and the tunnel current easily flows, and the tunnel distance of GaAs, for example,
It becomes possible to widen it to about 500 to 1000Å. In addition,
An undoped GaAs layer is interposed between the A 1 Ga As layer 17 and the n ⁺ −GaAs layer 19, which is undoped Al _0.05 Ga _0.95.
It is provided in the As layer 17 to prevent impurities from diffusing from the high-concentration n ⁺ -GaAs layer 19'.Since its thickness is thin, electrons are injected and the energy becomes the same as that of the n ⁺ -GaAs layer. In particular, this layer does not form its own barrier.

In addition, this manufacturing method uses an Al Ga As layer on the GaAs substrate 15.
17, undoped GaAs layer 18 ', n ⁺ -GaAs layer 19' are continuously epitaxially grown with good controllability, gold is deposited on them, and these are undoped GaAs by lithography.
The layers are etched to separately form the undoped GaAs layer, n ⁺ -GaAs layer, and gold (electrode) of the fine particles and the source and drain electrodes. Therefore, the source electrode 12 and the drain electrode 13 are made of gold.

Next, FIGS. 3 (a) and 3 (b) show an embodiment (II) diagram of a transistor according to the present invention. FIG. 3 (a) is a plan view and FIG. 3 (b) is the same diagram (a). ) Is a CC ′ cross-sectional view. The symbols in the figure are the same as those in the embodiment (I) shown in FIG. 1, but the other 27 are Al Ga As layers, and in this example, on the semi-insulating GaAs substrate 15. Undoped GaAs
Layer 18 'and n ⁺ -GaAs layer 19' are continuously epitaxially grown and etched to form fine grain undoped GaAs layer 1
After forming the 8, n ⁺ -GaAs layer 19 and gold 11 separately, Al _0.05 Ga is formed on the surface including the fine particles and the source electrode and between the fine particles and the drain electrode.
_In the structure in which the _0.95 As layer 27 is selectively epitaxially grown, tunneling is performed through the Al _0.05 Ga _0.95 As layer 27 provided on the side of the undoped GaAs layer, resulting in a low barrier as in FIG. 1 above and a wide tunnel length as well. It is possible and easy to manufacture.

Further, FIG. 4 shows an embodiment (III) of a transistor according to the present invention, which is only a plan view and a sectional view is shown in FIG.
This is the same as FIG. 3B, but this is different from the embodiment (II) shown in FIG. 3 in that the fine particles and the source electrode and the fine particles and the drain electrode through which the tunnel current substantially flows through the Al _0.05 Ga _0.95 As layer 27. The structure is such that it is left only in the region between and the other parts are removed, and the symbols in the figure are the same as those in FIG. The structure shown in FIG. 3 and the structure shown in FIG. 4 are selected in consideration of the device characteristics and the difficulty of manufacturing.

Although the above embodiment has been described by taking GaAs as an example, it goes without saying that the structure according to the present invention can be used for other semiconductors such as InP and InGaAs.

〔The invention's effect〕

As is clear from the above description of the embodiments, the structure of the fine particle transistor according to the present invention can be easily manufactured because the tunnel distance can be widened, and the wider the tunnel length, the smaller the dimensional deviation. The variation in the characteristics becomes small, and the effect of improving the quality of the transistor can be obtained.

[Brief description of drawings]

FIG. 1 is an embodiment (I) diagram according to the present invention, FIG. 2 is an energy band diagram seen in the embodiment (I), FIG. 3 is an embodiment (II) diagram according to the present invention, and FIG. FIG. 5 is a principle diagram of a transistor according to the present invention, FIG. 6 is its Id-Vd characteristic diagram, and FIG. 7 is a conventional example diagram. In the figure, 1 is fine particles, 2 and 12 are source electrodes, 3 and 13 are drain electrodes, 4 and 14 are gate electrodes, 5 is a semi-insulating InP substrate, 6 and 16 are SiO ₂ films, 11 is gold (fine particles). Conductive material), 15 is a semi-insulating GaAs substrate, 17, 27 is an Al _0.05 Ga _0.95 As layer (second semiconductor layer), 18, 18 'is an undoped GaAs layer, 19, 19' is an n ⁺ -GaAs layer (First semiconductor layer) is shown.

Claims (1)

(57) [Claims] 1. An island-shaped fine particle is provided between a source electrode and a drain electrode, and a tunnel current flows between the source electrode and the drain electrode through the fine particle, so that the tunnel current flows to the fine particle. In a transistor controlled by a voltage applied to a gate electrode coupled by a capacitance, the fine particles are composed of a conductive substance and a first semiconductor layer, and a second portion is provided between the fine particles and a source electrode and a drain electrode. A particulate transistor, characterized in that the height of a barrier against traveling carriers is determined by band discontinuity at the interface between the first semiconductor layer and the second semiconductor layer, which are coupled by a semiconductor layer.