RU2583866C1 - Metal-base transistor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention can be used for amplification, generation and conversion of electric signals. Invention presupposes that a transistor with a metal base containing an emitter, a base of the material with metal conductivity and a collector; at that, between the emitter and the base there is formed a Schottky barrier, the emitter is made of a semiconductor material with n⁺-type conductivity, the collector is made of a material with n-type conductivity, while between the base and the collector there is located a thin buffer layer of a material with p-type conductivity and between the base and the buffer layer there is formed an ohmic contact and between the buffer layer and the collector - a p-n-junction.

EFFECT: ensuring of a possibility to increase the static transfer ratio of the emitter current in a circuit with a common base.

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Description

The invention relates to the field of semiconductor micro- and nanoelectronics, namely to transistors containing an emitter, a base of a material with metallic conductivity and a collector, and can be used in various electronic devices and integrated circuits designed to amplify, generate and convert electrical signals.

A metal base transistor (TMB) is a unipolar transistor, since only electrons are used as charge carriers in it [1, 2]. Due to the possibility of a significant reduction in the thickness of the base, the electron motion in it is ballistic in nature without recombination processes, which reduces the noise in the transistor. In addition, due to the low specific resistivity of the metal, the transverse resistance of the metal base is much smaller than in conventional bipolar transistors, so the frequency properties of the TMB are improved. The use of a metal base also improves radiation resistance and reduces the power dissipation in the transistor.

However, in TMB, the static emitter current transfer coefficient in the circuit with a common base α is small and is in the range of 0.3-0.6, which is a significant drawback of such transistors. To eliminate this drawback, in [2] a TMB design was proposed containing an emitter junction, a base made of a material with metallic conductivity and a collector made of semiconductor material, the emitter junction made in the form of a conductor – insulator tunnel junction, and the dielectric is located between the emitter and the base. A direct voltage is applied to the emitter junction, the magnitude of which is sufficient to give the injected electrons the energy necessary to ionize the collector material and to form electron-hole pairs there, which leads to an increase in the collector current and, consequently, the transfer coefficient α. However, the process of ionizing the material in the collector increases the noise figure and degrades the frequency properties of the transistor.

Closest to the claimed device, selected as a prototype, is the device described in [1]. The prototype contains an emitter made of silicon with n-type conductivity, a base of cobalt disilicide (CoSi ₂ ) with metal conductivity and a silicon collector with a higher doping level than the emitter. The use of cobalt disilicide as a base instead of, for example, tungsten (W) or gold (Au) simplifies the manufacturing process of TMB, but does not eliminate the main disadvantage associated with a small value of α (α≅0.6).

The technical result of the invention is to increase the static emissivity of the emitter current in a circuit with a common base α to values greater than 0.95 while maintaining the advantages associated with the use of a base with metal conductivity.

The essence of the invention lies in the fact that in a transistor containing an emitter with an n ⁺ -type of conductivity, a base of material with metallic conductivity and a collector with an n-type of conductivity (n-region), a thin buffer layer of semiconductor material is placed between the base and the collector p-type conductivity (p-region). A Schottky barrier is formed between the emitter and the base, and an ohmic contact is formed between the base and the p-region. The collector is separated from the base by a pn junction. The electrons injected from the emitter ballistically fly through a thin base, then pass through the ohmic contact, p-region without reflections, then fall into the accelerating field of the pn junction, and a controlled collector current will appear. The proposed transistor is also unipolar, since in it only electrons are charge carriers.

It is known that the frequency properties of the transistor depend on the transition time of electrons from the emitter to the collector, therefore, the metal base and p-region must be very thin, and in the p-region it is advisable to form an internal electric field accelerating for electrons, for this the concentration of the doping acceptor impurity near the base should be higher than near a collector with n-type conductivity.

The proposed transistor with a metal base, in which a buffer layer with p-type conductivity is formed between the base and the collector, thereby eliminating the Schottky reflective barrier between the base and the collector in the prototype, which allows to obtain the claimed technical result.

The drawing shows a possible variant of the transistor in plan and its cross section, where 1 is a base of a material with metallic conductivity, 2 is a buffer layer of semiconductor material with p-type conductivity, 3 is a collector made of semiconductor material with p-type conductivity. An ohmic contact is made between the base and the p-region, and a rectifying contact (pn-junction) is formed between the p- and n-regions, 4 and 5 are depleted regions (space charge regions) in the p- and n-regions, respectively. To obtain ohmic contact with the output of collector 6, a region 7 with an n ⁺ type of conductivity is formed. An emitter 8 with an n ⁺ type of conductivity is located on the base 1, 9 is the output of the emitter, 10 is the output of the base. A Schottky barrier is formed between the emitter and the base.

The device works similarly to a conventional bipolar transistor. In a circuit with a common base, a negative voltage U _ЭБ relative to the base is supplied to the emitter, and a positive voltage U _{КБ is} also applied to the collector relative to the base. The voltage U _EB shifts the emitter junction (Schottky barrier) in the forward direction, which leads to the injection of electrons from the emitter into the base, and the voltage U _KB is the inverse of the collector junction (pn junction). The electrons injected from the emitter ballistically fly through a thin base, then pass a buffer layer of semiconductor material with p-type conductivity, then fall into the accelerating field of the pn junction, and a controlled collector current will appear.

In the proposed device, the value of the emitter current transfer coefficient α can be greater than in conventional bipolar transistors, since the device does not have a hole component of the emitter current. To reduce the time of flight of electrons through the p-region, it is necessary to reduce the thickness of the p-region, while the recombination current of electrons and holes in it will also decrease, which will lead to an increase in α. In addition, an accelerating internal electric field can be created in the p-region, then the time of flight of electrons through the region and, consequently, the recombination current will decrease, and the value of the emitter current transfer coefficient α will increase.

The device can be made of materials commonly used in semiconductor electronics, for example silicon, semiconductor materials of group A ^III B ^V as an emitter, p-region and collector, and as a base - cobalt disilicide (CoSi ₂ ), aluminum (Al), tungsten (W) and other materials allowing the formation of a Schottky barrier with an emitter and ohmic contact with the p-region.

The proposed transistor with a metal base will increase the value of the static emitter current transfer coefficient α and improve the amplifier properties of the device.

Information sources

1. Vikulin I.M., Stafeev V.I. Physics of semiconductor devices. - M .: Radio and communications, 1990 .-- S. 246-248.

2. Sins IV Transistor. Patent No. RU 2062531, C1, IPC: H01L 29/73, claimed 04/06/1992, publ. 06/20/1996.

Claims (1)

A transistor with a metal base containing an emitter, a base of material with metal conductivity and a collector, while a Schottky barrier is formed between the emitter and the base, characterized in that the emitter is made of a semiconductor material with an n ⁺ type of conductivity, the collector is made of a material with n- type of conductivity, and between the base and the collector a thin buffer layer of material with a p-type of conductivity is placed, while an ohmic contact is formed between the base and the buffer layer, and a pn junction between the buffer layer and the collector.

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