RU2517788C1 - Bipolar shf transistor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: bipolar SHF transistor based on heteroepitaxial structures includes on a substrate of single-crystalline silicon of p-type conductivity an in-series buffer layer of AlN, a layer of polycrystalline diamond with thickness of at least 0.1 mcm, an undoped buffer layer of GaN, a subcollector layer of GaN of n+type conductivity, a collector of GaN of n-type conductivity, a base of solid solution Al_yGa_1-yN, an intermediate layer of Al_yGa_1-yN of p+type conductivity, an emitter including Al_xGa_1-xN of n-type conductivity, contact layers, ohmic conductors and layers of insulating dielectric coating of polycrystalline diamond. Besides, formulas of the layers of Al_xGa_1-xN and Al_yGa_1-yN are different, with unequal concentration of a doping agent.

EFFECT: invention allows increase in the output SHF power, decrease in the emitter capacitance, resistance of base, capacitance of the collector-base, edge states of heterojunctions and allows high values of the emitter efficiency, limit frequency thus providing effective heat removal from the transistor active area.

2 cl, 1 dwg

Description

The invention relates to the field of semiconductor microelectronics, in particular to the design of bipolar transistors that can be used to create a microwave element base, and methods for their manufacture.

The main requirements for microwave semiconductor electronics now and in the near future are to increase the level of radiated microwave power and increase functionality while reducing the size and reducing power consumption.

In the prior art, a bipolar transistor is known which comprises an emitter, a base consisting of heavily doped and lightly doped regions, and a collector consisting of strongly and lightly doped regions (see UK Patent No. 1,523,012, publ. 08/31/1978).

A disadvantage of the known device is the insufficiently high power and the absence of heat removal from the active region of the transistor.

In addition, it is known a semiconductor device containing at least three regions of a semiconductor of alternating conductivity type, forming two pn junction. In this case, the first semiconductor region is made of two zones of different concentration, forming the L-H junction. Moreover, the zone adjacent to the pn junction has a lower impurity concentration than the second one, and the difference in concentrations provides an integrated field in the first region, balancing the diffusion current of minority carriers injected into it from the first pn junction, and the thickness of the first the region is shorter than the diffusion length of minority carriers in it (see A.S. USSR No. 640686, publ. 12/30/1978).

The disadvantage of this device is also not high enough power transistor.

The objective of the present invention is to remedy the above disadvantages.

The technical result of the invention is to increase the output microwave power, decrease the values of the emitter capacitance, the base resistance, collector-base capacitance, heterojunction boundary states and increase the emitter efficiency, the limiting frequency, and also ensure efficient heat removal from the active region of the transistor.

The technical result is ensured by the fact that the bipolar microwave transistor based on heteroepitaxial structures includes a buffer layer of A1N sequentially placed on a substrate of p-type single crystal silicon, an A1N buffer layer, a polycrystalline diamond layer having a thickness of at least 0.1 μm, undoped buffer a layer of GaN, a sub-collector layer of GaN n + of the conductivity type, a collector of GaN of n-type conductivity, a base of an Al solid solution _of Ga _1- N N, an intermediate layer of Al _y Ga _1- type N p + conductivity, emitter, including second Al _x Ga _1-x N _{n-conductivity} type contact layers, ohmic contacts and covering the dielectric insulating layers of polycrystalline diamond. In addition, the compositions of the layers of Al _x Ga _1-x N and Al _y Ga _1-y N are made different and with a different concentration of the dopant. In this case, a smooth change in the composition of the Al _y Ga _1-y N solid solution along the base and the intermediate layer was realized at a value of y from 0.00 in the region adjacent to the collector to a value of y equal to 0.12 in the region adjacent to the emitter. A smooth change in the concentration of the dopant along the base and the intermediate layer is realized from a value of 0.7 · 10 ¹⁹ cm ^-3 in the region adjacent to the collector region to a value of 2 · 10 ¹⁹ cm ^-3 in the region adjacent to the emitter region. The change in the composition of the Al _x Ga _1-x N solid solution along the emitter is realized at a value of x from 0.22 in the region adjacent to the region of the intermediate layer to a value of x equal to 0.25 in the region adjacent to the region of the first contact layer. A smooth change in the impurity concentration along the emitter is realized from a value of 5 · 10 ¹⁷ cm ^-3 in the region adjacent to the intermediate layer to a value of 8 · 10 cm ^-3 in the region adjacent to the region of the first contact layer.

The bipolar transistor may contain three layers of an insulating dielectric coating made of polycrystalline diamond, placed between the emitter base and the collector.

The essence of the present invention is illustrated in the drawing, which shows the device of the microwave bipolar transistor and the following structural elements are indicated:

1 - MD-40 brand flange;

2 - a layer of solder composition AuSn;

3 - a pedestal of heat-conducting polycrystalline diamond;

4 - sublayer of AuSn;

5 - substrate of single-crystal silicon p-type conductivity;

6 - buffer layer of A1N;

7 - CVD layer of polycrystalline diamond;

8 - undoped GaN buffer layer;

9 - subcollector layer;

10 - high resistance collector;

11 - base;

12 - an intermediate layer;

13 - the first layer of wide-band emitter;

14 - the second layer of the emitter;

15 - contact layer;

16 - contact layer;

17 - contact layer;

18 - contact layer;

19 - ohmic contact to the collector;

20 - ohmic contact to the base;

21 - ohmic contact to the emitter;

22 - a layer of insulating dielectric coating of polycrystalline diamond.

The present device is manufactured as follows.

On the flange of the brand MD-40 1 with a thickness of 1600 μm, a solder layer of AuSn 2, 25 μm thick, is placed on which a pedestal of heat-conducting polycrystalline diamond 3 0.15 mm thick is sealed. A ~ 25 μm thick sublayer AuSn 4 is placed on top of the pedestal 3, which subsequently serves as the basis for strengthening the transistor crystal to the pedestal 3. As the base substrate 5, p-type monocrystalline silicon oriented along the (111) plane is used. On the surface of the base substrate 5 with a buffer layer of A1N 6, 0.1 μm thick, deposited on it, a heat-conducting CVD layer of polycrystalline diamond 7 0.1 mm thick is placed. After that, the silicon base substrate 5 is drowned by well-known wet and dry etching methods to a thickness of 10 μm. Next, multilayer heteroepitaxial layers are sequentially placed: a buffer layer of undoped GaN 8, 200 nm thick, a sub-collector layer 9 of n + GaN type conductivity and 600 nm thick, doped with Si (to reduce the resistance of the ohmic contact of the collector), a high-resistance collector 10 is grown on top of the buffer layer of GaN with a thickness of 700 nm, doped with Si (to reduce the collector capacity and eliminate puncture of the base region). A layer of a thin base 11 of Al _y Ga _1-y N is sequentially placed on top of the high-resistance collector 10. The value of y in the solid solution along the base 11 changes: in the region adjacent to the collector 10, it is 0.00 and increases to 0.09 in the region adjacent to the region of the intermediate layer 12. The base thickness is 80 nm. The intermediate layer 12 is made of a solid solution of Al _y Ga _1-y N p + type conductivity. The value of y varies along the intermediate layer 12: in the region adjacent to base 11, it corresponds to 0.09, then gradually increases and reaches 0.12 in the region adjacent to emitter 13. The content of dopant (for example, magnesium) in the region varies: in the region of the base 11 adjacent to the collector 10, it is 0.7 · 10 ¹⁹ cm ^-3 and gradually increases to 2.0 · 10 ¹⁹ cm ^-3 in the region adjacent to the region of the emitter 13 (first layer of the emitter).

Next, the emitter layers 13 and 14 are placed, while the first layer is made of Al _x Ga _1-x N n-type conductivity. The value of x along the first layer 13 varies from 0.22 in the region adjacent to the intermediate layer 12 to 0.24 in the region adjacent to the second layer of the emitter 14. The layer 13 is made with a thickness of 80 nm. The impurity concentration varies from 5 · 10 ¹⁷ cm ^-3 in the region adjacent to the intermediate layer 12 to 7 · 10 ¹⁷ cm ^-3 in the region adjacent to the second layer of emitter 14. Layer 13 is doped with Si. The second layer of the emitter 14 is made of Al _x Ga _1-x N n-type conductivity. The value of x along the second layer of the emitter 14 varies, namely in the region adjacent to the first layer of the emitter 13, is 0.24, and changes smoothly to a value of 0.25 in the region adjacent to the first contact layer 15. The concentration of the impurity varies from 7 10 ¹⁷ cm ^-3 in the region adjacent to the first layer of the emitter 13, to a value of 8 · 10 ¹⁷ cm ^-3 in the region adjacent to the first contact layer 15. Layer 14 is doped with Si.

With this embodiment, in the region of the emitter 13, 14, as well as in the region of the base 11 and in the region of the intermediate layer 12, double accelerating drift fields for carriers arise. This is due to a change in the compositions of Al _x Ga _1-x N, Al _y Ga _1-y N solid solutions and dopants. Then, emitter mesa is etched, contact is formed to base 11, base mesa is etched, collector 10 is isolated, collector metallization is deposited, contact layers 15-18 are deposited, first layer of insulating polycrystalline diamond 22 is deposited, thin-layer resistor is deposited, contact windows are formed in insulating polycrystalline diamond , the formation of the wiring of the first level, the deposition of the second layer of insulating polycrystalline diamond, etching of the windows in the layer of insulating polycrystalline diamond and the formation of the second level of wiring, the deposition of the third layer of insulating polycrystalline diamond and etching of the windows under the contact pads, grinding and etching through holes on the back side, the deposition of galvanic gold on the back side.

The contact layer 15 is made of Al _x Ga _1-x N n-type conductivity. The value of x along the first contact layer 15 in the region adjacent to the second layer of the emitter 14 is 0.25 and changes smoothly to a value of 0.05 in the region adjacent to the second contact layer 16. A GaN contact layer 16 is sequentially placed on top of the first contact layer 15 n + type conductivity, the contact layer 17 of In _y Ga _1-y N. The value of y decreases from 0.05 (in the region adjacent to layer 15) to 0.5 (in the region adjacent to layer 18). The contact layer 18 is made of In _at Ga _1-y N at y = 0.5.

The contact layers 15-18 are expanded to reduce the transition resistance of the ohmic contact of the emitter 13, 14. The ohmic contacts (19, 21) to the collector and emitter are made by metallization from Ti / Al. This is the most common metallization system on the basis of which ohmic contacts are created. During annealing of the sprayed metallization system, Ti interacts with N. As a result, TiN is formed, which forms the basis of the contact, A1 serves as a diffusion barrier and stabilizes the contact. The ohmic contact to the base 20 is carried out by sputtering and subsequent annealing of Ni. The layers 22 of the insulating polycrystalline diamond with the corresponding metallization of the ohmic contacts are placed on the surface of the transistor crystal, between the emitter, the base and the collector.

The transistor case is an unpressurized cermet structure. The base is made of MD-40 (to ensure, firstly, the best heat dissipation from the transistor crystal, and secondly, matching the TCR of the metal and multicorrosive boards) and is coated with gold. Polycor core boards are installed in the case, between which there are GBT crystals. The connection of the contact pads of the crystal with the metallization of the boards is carried out by a gold wire by the method of thermal compression or ultrasound.

This device significantly reduces the time of flight of carriers, increases the limiting frequency, heat dissipation from the active region of the transistor and emitter efficiency, decreases the base resistance and emitter capacitance.

Claims (2)

1. A bipolar microwave transistor based on heteroepitaxial structures, including a buffer layer of AlN sequentially placed on a p-type silicon single crystal substrate, an AlN buffer layer, a polycrystalline diamond layer having a thickness of at least 0.1 μm, an undoped GaN buffer layer , sub-collector layer of GaN n + type of conductivity, collector of GaN n-type of conductivity, base from Al _y Ga _1-y N solid solution, intermediate layer of Al _y Ga _1-y N p + type of conductivity, emitter including Al _x Ga _1-x N n-type conductivity, contact sl ohms, ohmic contacts and layers of an insulating dielectric coating made of polycrystalline diamond, in addition, the compositions of the layers of Al _x Ga _1-x N and Al _y Ga _1-y N are made different and with a different concentration of the dopant, with a smooth change in the composition of the solid solution Al _y Ga _1-y N along the base and the intermediate layer is realized with a value of y from 0.00 in the region adjacent to the collector to a value of y equal to 0.12 in the region adjacent to the emitter, and a smooth change in the concentration of dopant along the base and intermediate layer implemented values of 0.7 × 10 ¹⁹ cm ^-3 in the region adjacent to the collector region, to a value of 2 × 10 ¹⁹ cm ^-3 in the region adjacent to the emitter region, the change in solid solution composition Al _x Ga _1-x N is realized along the emitter with a value of x from 0.22 in the region adjacent to the region of the intermediate layer to a value of x equal to 0.25 in the region adjacent to the region of the first contact layer, and a smooth change in the concentration of the impurity along the emitter is realized from a value of 5 · 10 ¹⁷ cm ^-3 in the region adjacent to the intermediate layer, to a value of 8 x 10 ¹⁷ cm ^-3 in the region adjacent to a domain of the first contact layer. 2. The bipolar transistor according to claim 1, characterized in that it contains three layers of an insulating dielectric coating of polycrystalline diamond, placed between the emitter base and the collector.

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