JPH05198855A - Low voltage operated dielectric base transistor - Google Patents

Abstract

PURPOSE:To realize low voltage operation, by specifying material which forms at least one of a base electrode, an emitter electrode, and a collector electrode, and substance which constitutes a part which comes into contact with a barrier layer of low dielectric constant and a base region of high dielectric constant. CONSTITUTION:The title transistor is constituted of the following; a base electrode 11 which comes into contact directly or indirectly with a base region 1 of high dielectric constant, and an emitter electrode 3 and a collector electrode 6 which come into contact with the base layer 1 of high dielectric constant via barrier layers 2, 5 whose dielectric constant is lower than that of the material forming the base region 1 of high dielectric constant. At least one of the base electrode 11, the emitter electrode 3, and the collector electrode 6 is composed of the same material as the material forming the base region 1 of high dielectric constant. The barrier layers 2, 5 of low dielectric constant or the part which comes into contact with the base region 1 of high dielectric constant are composed of substance to which conductivity is given by substituting a part of constituent elements by other elements or by generating element defect.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to low voltage operating dielectric base transistors used to amplify or switch electrical signals.

In the technical field of electronic devices for information processing represented by computers, transistors for amplifying and switching electric signals play an important role, and the characteristics of the transistors used in the electronic devices. It is of primary importance to improve the characteristics of electronic devices.

In particular, the improvement in the switching speed of transistors and the reduction in power consumption are directly linked to the improvement in the processing speed of electronic devices. Although there are various directions for increasing the speed and reducing the power consumption of a transistor, the basis thereof is the miniaturization or downsizing of the element size of the transistor. When the element size of the transistor is reduced,
Along with that, capacitance and inductance are reduced, which is effective for speeding up the operation, and speeding up by shortening the carrier travel distance in the transistor can be expected.

To reduce the power consumption of a transistor,
It is necessary to optimize not only the size of the device but also the device structure. Further, a low power consumption transistor in which the element size is minimized can be formed by using a metal, an oxide, a metal superconductor, or an oxide superconductor in addition to the conventionally used semiconductor material. If possible, the range in which the transistor can be applied will be greatly expanded, which is considered to be industrially useful.

[0005]

2. Description of the Related Art As a transistor which meets such a demand, a dielectric base transistor has been proposed. This dielectric base transistor is a general term for transistors using a dielectric in the base region, and has a structure in which the emitter electrode and the collector electrode are in contact with the high dielectric constant base region through a thin tunnel barrier layer.

The base electrode directly contacts the high dielectric constant base region, and the voltage applied to the base electrode controls the potential of the high dielectric constant base region. When the potential of the high-dielectric-constant base region changes, the amount of carriers injected from the emitter electrode through the tunnel barrier layer into the high-dielectric-constant base region changes, so that the current between the base electrode and the collector electrode is controlled. It

FIGS. 6A and 6B are explanatory views of a conventional dielectric base transistor. FIG. 6A shows a schematic structure of a conventional dielectric base transistor, and FIG.
Shows the current-voltage characteristics of this transistor. Figure 6
(A) shows a schematic structure of a conventional dielectric base transistor of a planar type in which an emitter electrode and a collector electrode are in contact with the same side surface of a high dielectric constant base region.

In this figure, 81 is a high dielectric constant base region, 82 and 84 are barrier layers, 83 is an emitter electrode, and 85 is an emitter electrode.
Is a collector electrode, 86 is an insulator layer, 87 is an emitter wiring, 88 is a collector wiring, and 89 is a base electrode.

In this dielectric base transistor, a high dielectric constant base region 81 made of a SrTiO ₃ substrate is used.
The emitter electrode 8 made of Ta through a barrier layer 82 made of Si having a thickness of 60Å through which carriers are tunneled to the upper surface of the
3 is formed, and a collector electrode 85 made of Ta is formed apart from the emitter electrode 83 via a barrier layer 84. And the insulator layer 86 deposited thereon
An emitter wiring 87 and a collector wiring 88 made of Ta are formed through the contact hole. A base electrode 89 made of Pt is directly formed on the back surface of the high dielectric constant base region 81.

An example of the current-voltage characteristic of this conventional dielectric base transistor is shown in FIG. 6B, and a voltage gain of about 2 is obtained. The current gain of this transistor is extremely high because the high dielectric constant base region is insulating and the base current does not flow. That is, the conventional dielectric base transistor shown here has an extremely large current gain like the FET.

[0011]

However, the operating voltage of this dielectric base transistor is about several tens of volts, which is significantly higher than that of a normal transistor. When the operating voltage is high, it is difficult to incorporate it into a circuit together with a conventionally used semiconductor element that operates at a low voltage because the power supply voltage becomes uneven, which is an obstacle to reducing the power consumption of the circuit element. It is necessary to set the operating voltage of this dielectric base transistor to several V or less.

An object of the present invention is to solve the above problems and provide a dielectric base transistor capable of operating at a low voltage.

[0013]

In order to achieve the above object, a low-voltage operating dielectric base transistor according to the present invention has a high dielectric constant base region and a direct or indirect connection with the high dielectric constant base region. A base electrode that is in physical contact with
The base electrode is composed of an emitter electrode and a collector electrode that are in contact with the high dielectric constant base region through a barrier layer having a dielectric constant lower than that of the material forming the high dielectric constant base region,
At least one of the emitter electrode and the collector electrode is made of the same material as the material forming the high-dielectric constant base region, and a portion in contact with the low-dielectric constant barrier layer or the high-dielectric constant base region is a part of its constituent elements. Was replaced with another element, or a deficiency of the element was generated, so that a structure made of a material to which conductivity was imparted was adopted.

In this case, a barrier layer that substantially prohibits carrier flow can be interposed between the base electrode and the high dielectric constant base region.

Further, in this case, the emitter electrode or the collector electrode can be formed of a superconducting or normal conducting oxide. In addition, the high dielectric base region is set to Sr, T
It can be formed of a perovskite-based dielectric material made of an oxide containing any one of i, Ta, K, Sn, Zr, and Nb.

Further, the high dielectric base region is set to KTa _1-x Nb.
formed by _x O _3, the base electrode material this KTa _1-x N
It can be formed by adding conductivity by replacing a part of K of b _x O ₃ with Ca.

[0017]

In order to solve the problem of the conventional dielectric base transistor described above, first, what factor determines the operating voltage of the dielectric base transistor will be examined.

FIG. 7 is an energy band diagram of a conventional dielectric base transistor. This figure shows the energy band between the emitter and collector electrodes of a conventional dielectric-based transistor. In this figure, 83 is an emitter electrode, 82 is a barrier layer, 81 is a high dielectric constant base region, 84 is a barrier layer, and 85 is a collector electrode.

The emitter electrode 83 and the collector electrode 85 are formed of a conductive region such as a metal, a semiconductor, a metal or oxide superconductor, and the barrier layers 82, 84.
Are formed by a thin insulator layer that acts as a tunnel barrier to the flow of carriers,
1 is made of a material having an insulating band structure. Although not shown, the base electrode is formed in direct contact with the high dielectric constant base region 81.

In order for a large current to flow through this dielectric base transistor, the emitter electrode 8 must be activated in the operating state.
It is necessary that the injection of carriers into the high dielectric constant base region 81 from 3 is large, that is, the height of the conduction band of the high dielectric constant base region 81 is lower than the Fermi level of the emitter electrode.

The potential of the high dielectric constant base region 81 at the interface between the emitter electrode 83 and the high dielectric constant base region 81 is determined by the voltage of the collector electrode 85 and the voltage of the base electrode (not shown). .. Also, the collector electrode 8 necessary for lowering the height of the conduction band of the high dielectric constant base region 81 below the Fermi level of the emitter electrode 83.
The voltage of 5 and the voltage of the base electrode will be proportional to the height of the conduction band of the high dielectric constant base region 81 when these voltages are zero.

That is, as the height of the conduction band of the high dielectric constant base region in the zero voltage applied state is higher, the voltage of the collector electrode and the voltage of the base electrode required to flow the current through the dielectric base transistor are higher. ..

From this point of view, in the conventional dielectric base transistor shown in this figure, the voltage of the collector electrode and the voltage of the base electrode required to flow a current through the dielectric base transistor are high. I understand.

Therefore, in order to lower the operating voltage, it is necessary to lower the height of the conduction band of the high dielectric constant base region to near the Fermi level of the emitter electrode. As a method for this, the barrier height when the barrier layer is viewed from the base electrode, the emitter electrode or the collector electrode (the barrier height measured from the Fermi level of the electrode) and the barrier layer when viewed from the high dielectric constant base region are used. It suffices to make the heights (the magnitudes of the conduction band shifts) equal.

In order to realize the barrier height relationship,
The base electrode, emitter electrode or collector electrode and the high-dielectric-constant base region are made of the same material, and the region to become the emitter electrode or collector electrode is doped with appropriate impurities to make this region a degenerate semiconductor, or part of the composition is replaced. Moreover, conductivity can be imparted by creating compositional defects.

According to this method, the conduction band of the high-dielectric-constant base region is automatically located in the vicinity of the Fermi level of the collector electrode and the base electrode when the voltages of the collector electrode and the base electrode are zero. Also, even at the base voltage, the conduction band of the high-dielectric-constant base region becomes lower than the Fermi level of the emitter electrode, so that the operation of the dielectric base transistor can be lowered.

FIG. 8 is an energy band diagram of the low voltage operating dielectric base transistor of the present invention. This energy band diagram shows a schematic energy band from the emitter electrode to the collector electrode. Although this figure is for the case where the carrier is an electron, the same explanation can be applied when the carrier is a hole.

In this figure, a is an emitter electrode, b is a barrier layer, c is a high dielectric constant base region, d is a barrier layer, and e.
Is a collector electrode.

The emitter electrode a and the collector electrode e
Is formed by replacing a part of the element of the same material as the material forming the high dielectric constant base region c with another element or by causing a deficiency of the element to give conductivity. The barrier layers b and d are formed of a thin insulating layer that acts as a tunnel barrier against the flow of carriers, and the high dielectric constant base region 3 is formed of a material having an insulating band structure. Although not shown, the base electrode is formed in the high dielectric constant base region c directly or via an insulating layer.

As shown in this figure, according to the present invention, the conduction band of the high-dielectric-constant base region is automatically located near the Fermi level of the emitter electrode and the collector electrode. Low voltage is possible.

[0031]

EXAMPLES Examples of the present invention will be described below. (First Embodiment) FIG. 1 is a block diagram of a low voltage operating dielectric base transistor of the first embodiment. In this figure, 1
Is a SrTiO ₃ substrate, 2, 5 are CeO ₂ thin films, 3, 6,
11 is a SrTiO ₃ : Nb layer, 4 and 7 are Ta layers, 8 is S
An SiO ₂ insulating layer, 9 is a Ta emitter wiring, and 10 is a Ta collector wiring.

In the low voltage operating dielectric base transistor of this embodiment, SrTi serving as the high dielectric constant base region is formed.
On the O ₃ substrate 1, SrTiO ₃ : Nb obtained by doping SrTiO ₃ with Nb through a CeO ₂ thin film 2 having a thickness of 2 nm.
An emitter electrode composed of the layer 3 and the Ta layer 4 is formed, and the CeO ₂ thin film 5 and SrTiO 3 are separated from the emitter electrode.
₃ : A collector electrode composed of the Nb layer 6 and the Ta layer 7 is formed, and 2000 Å thick SiO deposited on the collector electrode.
_{2 A} Ta emitter wiring 9 and a Ta collector wiring 10 are formed through the contact holes of the insulating layer 8 and SrTi ₃ is formed on the other side of the SrTiO ₃ substrate 1 which becomes a high dielectric constant base region.
A base electrode made of an O ₃ : Nb layer is directly formed.

The Ta layers 4 and 7 mentioned above are T
The SrTiO ₃ : Nb (strontium titanate) layers 3 and 6 below these are a part of the electrodes formed for extracting the current to the a-wiring, and actually become the emitter electrode or collector electrode.

In this case, Nb of the SrTiO ₃ : Nb layers _{3, 6} , 11 forming part of the emitter electrode, the collector electrode and the base electrode replaces Ti atoms in SrTiO ₃ and has a concentration of 0.05%. Sufficient conductivity is imparted. The distance between the emitter electrode and the collector electrode is 0.
It is 5 μm. In addition, the SrTiO ₃ : Nb layers 3, 6 and Sr
2 nm thick Ce interposed between the TiO ₃ substrates 1
The O ₂ thin films 2 and 5 function as tunnel barrier layers.

In the above description, S is added to the high dielectric constant base region.
Although rTiO ₃ was used, other Sr, Ti, Ta,
A perovskite-based dielectric that is an oxide containing any of K, Sn, Zr, and Nb can be used.

(Second Embodiment) FIG. 2 is a block diagram of a low voltage operating dielectric base transistor of the second embodiment. In this figure, 21 is a SrTiO ₃ substrate, 22, 25, 31
Is a CeO ₂ thin film, 23, 26 and 32 are SrTiO ₃ : N
b layer, 24 and 27 are Ta layers, 28 is a SiO ₂ insulating layer, 2
Reference numeral 9 is a Ta emitter wiring, and 30 is a Ta collector wiring.

In the low voltage operating dielectric base transistor of this embodiment, SrTi serving as the high dielectric constant base region is formed.
An emitter electrode composed of a SrTiO ₃ : Nb layer 23 and a Ta layer 24 is formed on an O ₃ substrate 21 via a CeO ₂ thin film 22 having a thickness of 2 nm. ₂ SrTiO 3 through the thin film 25
₃ : A collector electrode composed of the Nb layer 26 and the Ta layer 27 is formed, and S having a thickness of 2000 Å deposited on the collector electrode.
A Ta emitter wiring 29 and a Ta collector wiring 30 are formed through the contact holes of the iO ₂ insulating layer 28, and S
_On the other side of the rTiO ₃ substrate 21, a 4 nm thick CeO ₂ substrate is formed.
A base electrode 32 made of a SrTiO ₃ : Nb layer is formed via a thin film 31.

The low-voltage operation dielectric base transistor of this embodiment is different from that of the first embodiment in that a CeO ₂ thin film 31 having a thickness of 4 nm is interposed between the base electrode 32 and the base region 21. The 4 nm thick CeO ₂ thin film 31 prevents carriers from flowing into the base electrode 32, so that there is an advantage that the base current does not flow under any bias condition and the current amplification factor can be improved.

(Third Embodiment) FIG. 3 is a block diagram of a low voltage operating dielectric base transistor of the third embodiment. In this figure, 41 is a LaAlO ₃ substrate, 42, 45, 48.
Is a SrTiO ₃ : Nb layer, 43 is a SrTiO ₃ layer, 4
4, 47 are CeO ₂ thin films, 46 and 49 are Ta layers, 50 is a SiO ₂ insulating layer, 51 is Ta emitter wiring, and 52 is Ta.
The collector wiring and 53 are Ta base wirings.

In the low-voltage operation dielectric base transistor of this embodiment, a 1 μm thick SrTiO ₃ : Nb layer 42 is deposited on an insulating LaAlO ₃ substrate 41, and a SrTiO ₃ layer 43, thickness is formed thereon. An emitter electrode composed of a SrTiO ₃ : Nb layer 45 and a Ta layer 46 is formed via a ₂ nm CeO ₂ thin film 44, and the SrT is separated from the emitter electrode by a 2 nm thick CeO ₂ thin film 47.
A collector electrode composed of an iO ₃ : Nb layer 48 and a Ta layer 49 is formed, and a thickness of 2000Å deposited on the collector electrode.
Through the contact hole of the SiO ₂ insulating layer 50 of
An a emitter wiring 51, a Ta collector wiring 52, and a Ta base wiring 53 are formed.

The low-voltage operation dielectric base transistor of this embodiment is different from that of the first embodiment in that the base electrode S is used.
rTiO ₃ : Nb layer 42, S serving as a high dielectric constant base region
Each of the rTiO ₃ layers 43 is a thin film and has an insulating La
That is, it is deposited on the AlO ₃ substrate 41.

The shape and dimensions of the other parts are the same as those of the first embodiment, but the SrTiO ₃ : Nb layer 4 serving as the base electrode is formed.
In order to prevent the insulating layer 50 from being broken due to the step at the edge of the second edge, the edge is etched by ion milling so that the cross section has an inclination. This embodiment has an advantage over the first embodiment in that a plurality of dielectric base transistors can be integrated on the same substrate.

(Fourth Embodiment) FIG. 4 is a block diagram of a low voltage operating dielectric base transistor of the fourth embodiment. In this figure, 61 is a SrTiO ₃ substrate, and 62 and 64 are YA.
lO ₃ film, 66 YAlO ₃ insulating layer, 63,65,6
Reference numerals 7, 68 and 69 are YBa ₂ Cu ₃ O _x layers.

Low-voltage operation dielectric base transistor of this embodiment
In the transistor, SrTi becomes the high dielectric constant base region.
O₃On the substrate 61, YA that becomes a barrier layer with a thickness of 2 nm
10 ₃High-temperature superconductivity that serves as an emitter electrode through the thin film 62
The body is YBa₂Cu₃O_xLayer 63 is formed and this layer is
Separated from the mitter electrode, YAlO₃Through the thin film 64
YBa to be the collector electrode₂Cu₃O_xLayer 65 is formed
And YAlO with a thickness of 3000 Å deposited on it
₃Emitters are distributed through the contact holes in the insulating layer 66.
YBa that becomes a line₂Cu₃O_xLayer 67 and collector wiring
YBa₂Cu ₃O_xThe layer 68 is formed and has a high dielectric constant.
SrTiO that becomes the area₃On the other side of the substrate 61
YBa at the pole₂Cu₃O_xThe layer 69 is formed directly
It

The low-voltage operation dielectric base transistor of this embodiment differs from that of the first embodiment in that the conductive parts such as the emitter electrode, collector electrode and base electrode are made of YBa ₂ Cu ₃ O _x which is a high temperature superconductor. Therefore, not only the advantage that the electrode resistance of the conductive portion becomes zero is obtained, but the sensitivity of the dielectric base transistor is improved by the superconducting state of the emitter electrode and the collector electrode. There are also advantages.

In this example, SiO ₂ was used as the insulating layer.
Reason for not using the, SiO ₂ is for degrading the superconductivity of YBa ₂ Cu ₃ O _x reacts with YBa ₂ Cu ₃ O _x. YAlO ₃ does not react with YBa ₂ Cu ₃ O _x . In this embodiment, an example using an oxide high temperature superconductor is shown, but it is obvious that a metal superconductor such as Nb or Pb can also be used.

(Fifth Embodiment) FIG. 5 is a block diagram of a low voltage operating dielectric base transistor of the fifth embodiment. In this figure, 71 is a KTa _1-x Nb _x O ₃ substrate, 72, 7
4 is a CeO ₂ thin film, 73 and 75 are SrTiO ₃ : Nb
Layer, 76 is a SiO ₂ insulating layer, 77 is Ta emitter wiring,
78 is Ta collector wiring, 79 is KTa _1-x Nb
_{xO 3} : Ca layer.

In the low voltage operating dielectric base transistor of this embodiment, KTa serving as the high dielectric constant base region is formed.
_{On the 1-x} Nb _x O ₃ substrate 71, CeO ₂ with a thickness of 2 nm is formed.
An emitter electrode composed of the SrTiO ₃ : Nb layer 73 is formed via the thin film 72, and a collector electrode composed of the SrTiO ₃ : Nb layer 75 is formed apart from the emitter electrode via the CeO ₂ thin film 74. The Ta emitter wiring 77 and the Ta collector wiring 78 are formed through the contact holes of the SiO ₂ insulating layer 76 having a thickness of 3000 Å deposited on the upper surface of the Ta layer to form the high dielectric constant base region KTa.
_On the other side of the _1-x Nb _x O ₃ substrate 71, KTa _1-x Nb _x O
KTa _1-x with conductivity added by replacing K in ₃ with Ca
The base electrode composed of the Nb _x O ₃ : Ca layer is directly formed.

The low-voltage operation dielectric base transistor of this embodiment
The difference from the first embodiment is that the transistor is a high dielectric base region.
Material of KTa_1-xNb_xO₃And the base electrode is K
Ta _1-xNb_xO₃Replace part of K in the composition with Ca
KTa that has been made electrically conductive _1-xNb_xO₃: For Ca layer
It has become.

In this embodiment, the temperature at which the dielectric constant becomes maximum can be adjusted by changing the ratio x of Nb. For example, by adjusting x so that the dielectric constant becomes maximum at the liquid nitrogen temperature, the liquid The advantage is that the device can be designed to have good characteristics at the nitrogen temperature. By the way, x = 0.0
At 5, the relative dielectric constant at the liquid nitrogen temperature reaches tens of thousands.

[0051]

As described above, according to the present invention, since the position of the conduction band of the base layer in the zero bias state can be brought close to the Fermi level of the emitter electrode, the dielectric base transistor having a low operating voltage. Can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a low voltage operating dielectric base transistor of a first embodiment.

FIG. 2 is a configuration diagram of a low voltage operating dielectric base transistor of a second embodiment.

FIG. 3 is a configuration diagram of a low voltage operating dielectric base transistor of a third embodiment.

FIG. 4 is a configuration diagram of a low voltage operating dielectric base transistor of a fourth embodiment.

FIG. 5 is a configuration diagram of a low voltage operating dielectric base transistor of a fifth embodiment.

6A and 6B are explanatory views of a conventional dielectric base transistor.

FIG. 7 is an energy band diagram of a conventional dielectric base transistor.

FIG. 8 is an energy band diagram of a low voltage operating dielectric base transistor of the present invention.

[Explanation of symbols]

1 SrTiO ₃ substrate 2,5 CeO ₂ thin film 3,6,11 SrTiO ₃ : Nb layer 4,7 Ta layer 8 SiO ₂ insulating layer 9 Ta emitter wiring 10 Ta collector wiring

Claims (6)

[Claims] 1. A high dielectric constant base region, and a base electrode which directly or indirectly contacts the high dielectric constant base region,
The base electrode is composed of an emitter electrode and a collector electrode that are in contact with the high dielectric constant base region through a barrier layer having a dielectric constant lower than that of the material forming the high dielectric constant base region,
At least one of the emitter electrode and the collector electrode is made of the same material as the material forming the high-dielectric constant base region, and a portion in contact with the low-dielectric constant barrier layer or the high-dielectric constant base region is a part of its constituent elements. A low-voltage operating dielectric base transistor, characterized in that it is made of a material to which conductivity is imparted by replacing the element with another element or causing a deficiency of the element. 2. The low voltage operating dielectric base according to claim 1, further comprising a barrier layer interposed between the base electrode and the high dielectric constant base region for substantially inhibiting carrier flow. Transistor. 3. The low voltage operating dielectric base transistor according to claim 1, wherein the emitter electrode or the collector electrode is made of a superconducting or normal conducting oxide. 4. The high dielectric base region is Sr, Ti, T
The low voltage operating dielectric base transistor according to claim 1, which is an oxide containing any one of a, K, Sn, Zr, and Nb. 5. The high dielectric base region is KTa _1-x Nb _x
It is made of O ₃ and the material of the base electrode is KTa _1-x Nb.
The low voltage operating dielectric base transistor according to claim 1, wherein conductivity is imparted by replacing a part of K of _x O ₃ with Ca. 6. The low voltage operating dielectric base transistor according to claim 1, wherein the high dielectric constant base region is a thin film formed on an insulating substrate. ..