JPH11274381A - Heat radiating structure of bypolar transistor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an emitter ballast resistor which provides stable operation and is easily manufactured by providing the emitter ballast resistor on each connecting conductor from each emitter electrode and by forming a heat flow path that reaches a rear face metal layer from the emitter electrode. SOLUTION: In a current path, each connecting conductor 15 from each emitter electrode 1 to a collected wiring 16 is separately provided from an air bridge conductor 2, an emitter ballast resistor 14 is connected to each connecting conductor 15, and the collected wiring 16 is connected to a grounding pad 17. Then a heat flow path reaches a rear face metal layer 92 from an emitter electrode 11, through an air bridge metal conductor 2, a heat sink 3 and a semi-insulating semiconductor layer 91. Heat is dissipated from the rear face metal layer 92 to the outside of the device. Therefore, each emitter of the respective transistor is grounded through each ballast resistor 14, the emitter current of each unit transistor is stabilized by the ballast resistor 14, and the operation of the transistor is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-finger type bipolar transistor formed on a substrate, and more particularly, to a bipolar transistor having a structure for improving heat radiation characteristics from an emitter.

[0002]

2. Description of the Related Art A multi-finger type bipolar transistor is formed by arranging a large number of unit transistors on a substrate, and each unit transistor is electrically isolated by providing an insulating layer in the substrate between the unit transistors. The electrodes of the transistors are arranged in parallel on the upper surface on the substrate side, and are respectively collected on the collective wiring via the leads.

The heat generated during the operation of the bipolar transistor is generated at the junction between the base region and the collector region of the semiconductor layer and is usually designed to be dissipated from the collector region to the back side of the substrate. Heat is also actively dissipated from the emitter electrode immediately above the region.

FIGS. 8A and 8B show an example of a GaAs high frequency NPN type bipolar transistor, in which a metal conductor 2 is formed into an air bridge 2 from an emitter electrode 11 protruding on a substrate 9 and is used as an emitter. It is connected to the heat sink 3 formed on the semi-insulating semiconductor layer 91 so as to straddle the other parallel electrodes, that is, the base electrode 7 and the collector electrode 8, and to transfer heat from the emitter electrode to the heat sink half. The light passes through the insulating semiconductor layer 91 and diffuses to the substrate back surface metal layer 92.

Further, conventionally, in order to increase the thermal conductivity of the semi-insulating semiconductor layer 91, this type of bipolar transistor has a via hole 4 as shown in FIG.
To connect the heat sink 3 and the back metal layer 92. The via hole is formed by forming a plating alloy layer on the inner surface of the through hole 42 of the semi-insulating semiconductor layer 91 to enhance heat conduction.

In a multi-finger type bipolar transistor, a ballast resistor is inserted into the emitter in order to stabilize the operation of each unit transistor and make the heat generation uniform. As the ballast resistance, for example, a method of increasing the distributed resistance of the impurity diffusion layer forming the emitter region of the transistor and adding a ballast resistance is adopted. Japanese Patent Application Laid-Open No. 9-181886 discloses NP
For an N-type silicon bipolar transistor, an emitter contact is formed on the stripe-type emitter region so as to be away from the base contact side to form an emitter ballast resistor, and the arrangement and shape of the emitter contact are adjusted. A technique for adjusting ballast resistance is disclosed.

Further, with respect to a GaAs-based high-frequency NPN bipolar transistor, the emitter layer (n-GaAs) of the bipolar transistor formed on a GaAs substrate is used.
An n-AlGaAs epitaxy layer is interposed as a resistance layer between the s layer) and the emitter contact layer (n-InGaAs epitaxy layer) to impart a ballast resistance to the emitter and operate each transistor uniformly. I was

[0008]

However, in a bipolar transistor of the type that dissipates heat also from the emitter,
In a structure in which a ballast resistor layer is interposed on the emitter electrode side, the ballast resistor increases the resistance of heat generated in the collector-base region and flowing to the emitter. For example, in the GaAs-based bipolar transistor, n-Al
The thermal resistance increases by the thickness of the GaAs epitaxy layer.

Further, the ballast resistor n-AlGaAs
The layer is formed of an epitaxy-grown layer, but it is difficult to form a ballast resistance layer having an accurate and stable resistance value.
A certain electrical resistance due to the AlGaAs layer, e.g.
In order to obtain a resistance of 5Ω with an emitter size of 2 × 20 μm in cross section, the doping concentration of the n-AlGaAs layer is lowered (5 × 10 ¹⁶ / cm ³ or less) and 2000 °
The above thickness was required, and it was difficult to achieve reproducibility and uniformity of the resistance value.

In view of the above problems, an object of the present invention is to provide a bipolar transistor device in which a unit transistor has a stable operation and has an emitter ballast resistor which is easy to manufacture. Another object of the present invention is to provide a bipolar transistor device that efficiently dissipates heat from an emitter.

[0011]

The bipolar transistor device of the present invention is a bipolar transistor device in which a large number of unit bipolar transistors are arranged in a finger shape on a substrate. The characteristics of the bipolar transistor device are intended to stabilize the emitter ballast resistance. Is provided with an emitter ballast resistor on each connection conductor from each emitter electrode of each unit bipolar transistor to the collective wiring, and further provided with a heat flow path from the emitter electrode of each unit bipolar transistor to the back metal layer of the substrate. It consists of

Since the formation of the ballast resistor for the emitter on the connection conductor with the emitter can be performed relatively easily and accurately, the emitter ballast resistor can be stabilized. As the ballast resistor, a metal thin film formed on a substrate by being arranged in series with an electric wiring path of each emitter electrode is used.

[0013] The bipolar transistor device of the present invention comprises:
In order to efficiently dissipate the heat from the emitter, the heat flow path includes an air bridge conductor connected to the emitter electrode, a semi-insulating semiconductor layer of a substrate thermally connected to the air bridge conductor, And a backside metal layer bonded to the conductive semiconductor layer, wherein the emitter electrode and the backside metal layer are electrically insulated. With this configuration, the heat flow path from the emitter electrode and the current path are separated, and the heat flow path does not include the emitter ballast resistance, thereby reducing the heat resistance and heat generation.
The efficiency of radiation can be increased.

In particular, according to the present invention, the heat flow path includes a via hole thermally connected to the air bridge conductor and the back metal layer of the substrate and inserted into the semi-insulating semiconductor layer.
The via holes promote heat transfer from the air bridge conductor to the backside metal layer of the substrate to ensure heat dissipation.

The via hole is opened to the upper surface side of the substrate and connected to an air bridge conductor or a heat sink, and the bottom portion of the via hole is electrically insulated and thermally connected to the metal layer on the back surface of the substrate. Is done. According to the present invention, in order to ensure electrical insulation and thermal conduction, the bottom of the via hole is stopped by the semi-insulating semiconductor layer or a separate insulating layer that is in contact with the metal layer on the back surface of the substrate.

The via hole is opened from the back side of the substrate and connected to the back metal layer, and the bottom of the via hole is electrically insulated and thermally connected to an air bridge conductor or a heat sink on the substrate. Is also adopted. In order to ensure electrical insulation and thermal continuity, the bottom of the via hole is stopped at the semi-insulating semiconductor layer or a separate insulating layer that is in contact with the heat sink directly or via an insulating layer. Have been.

The via hole is formed on the substrate adjacent to the unit bipolar transistor, and the number of via holes with respect to the number of unit bipolar transistors can be arbitrarily determined. Preferably, the unit bipolar transistors and the via holes are formed alternately at a ratio of 1: 1. Also, via holes
The two adjacent unit bipolar transistors can be shared as a heat flow path from the emitter electrode. In this case, two air bridge conductors extending from two adjacent emitter electrodes to one via hole between them are preferably provided with an appropriate insulator so as not to be electrically short-circuited with each other. This is because if the air bridge conductor from the emitter electrode of the adjacent unit bipolar transistor becomes electrically conductive, the significance of providing a ballast emitter resistor for each unit bipolar transistor is lost.

The bipolar transistor of the present invention has a
It is widely used for a finger array transistor using a substrate such as a system, InP system, and GaAs system, and is particularly suitable for a transistor for high frequency power amplification.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the following, embodiments of a bilateral transistor according to the present invention will be described with reference to an example of a heterojunction bipolar transistor having a multi-finger arrangement for a GaAs high-frequency output.

FIG. 1 shows the structure of the bipolar transistor.
As shown in (B), a large number of NPN unit transistors are arranged in parallel on a substrate via a semi-insulating semiconductor layer 91, and each transistor is formed of a semi-insulating GaAs substrate 9 having a semi-insulating property. A collector contact layer (n ⁺ −) formed on the semiconductor layer 91 by a molecular beam epitaxy method or the like.
GaAs layer) 81, collector layer 80 (n-GaAs layer)
, A base layer (p ⁺ -GaAs layer) 70, an emitter layer (n-AlGaAs layer) 10, and an emitter contact layer (n ⁺ -InGaAs layer) 12 are arranged in this order in the vertical direction to constitute a collector. A pair of collector electrodes 8 and 8 are joined to both sides of the contact layer 81, a pair of base electrodes 7 and 7 are formed to both sides of the base layer 70, and the emitter electrode 11 is formed to the emitter contact layer 12.
Are formed, and these electrodes are arranged in stripes on the upper side of the substrate.

A semi-insulating semiconductor layer 91 is formed between adjacent unit transistors 1 and 1 so as to reach the growth layer and a part of the substrate 9. Insulation is secured. Further, a back surface metal layer 92 is formed on the entire back surface of the substrate 9.

A metal heat sink 3 is connected to the semi-insulating semiconductor layer 91, the emitter electrode 1 and the heat sink 3 are directly connected by the air bridge metal conductor 2, and further, the whole surface is formed on the back surface of the substrate. A back metal layer 92 is formed on the base layer 70 on the collector layer 80 side of each unit transistor 1, 1.
A part of the heat generated in the junction region with the emitter electrode 11 on the emitter side, the air bridge metal conductor 2 and the heat sink 3
The light is dissipated along a path (indicated by a white arrow in the drawing) reaching the back metal layer 92 via the semi-insulating semiconductor layers 91 and 90 immediately below. Thus, the back metal layer 9 of the substrate 9 is separated from the emitter electrodes 11 of each unit bipolar transistor.
2 is provided.

Further, part of the heat generated in the junction region of each unit transistor with the base layer on the collector layer 80 side is:
The semi-insulating semiconductor layer 91 is moved to a position directly below the collector layer 80.
Is dissipated to the back metal layer 92 via the

Embodiment 1 In the basic example of the present invention, as shown in FIG.
Are provided separately from the air bridge conductor 2, and each of the connection conductors 15 is connected to the collective wiring 16.
Is connected to an emitter ballast resistor 14.
The collective wiring 16 is connected to the ground pad 17 in this example, so that each emitter of each transistor is grounded via the corresponding ballast resistor 14, and each unit transistor is connected to the emitter current by the ballast resistor 14. Is stabilized, and the operation of the transistor is stabilized.

As each ballast resistor 14, a resistive thin film formed on a substrate in series with an electric wiring path of each emitter electrode is used. The resistance thin film 14 is made of, for example, WSiN
, For example, a 500 ° thick deposited film. An example of such a resistive thin film 14 is 6 μm ×
A ballast resistor of about 10Ω can be obtained with a shape of 40 μm. For the connection conductor 15, the collective wiring 16, and the ground pad 17 for the emitter, a metal conductor similar to the conventional one, for example, a combination of an Au film on a Ti film can be used.

In the other heat flow path, since the air bridge metal conductor 2 is directly joined to the emitter electrode 11, the heat flow passing through the air bridge metal conductor 2 does not pass through the resistance thin film of the ballast resistor 14 and hinders the heat flow. Does not occur. The air bridge metal conductor 2 or the heat radiating plate 3 needs to be electrically floating from the ground.
The heatsink 3 or the emitter electrode 11 is substantially electrically insulated from the back metal layer 92 by the and the semi-insulating semiconductor layer 91. Further, it is necessary that the emitters 11 of adjacent unit transistors are also electrically disconnected. If the emitters 11 and 11 are conductive, they have the same potential, and there is no point in providing the ballast resistor 14 individually for each emitter. For this purpose, the air bridge metal conductors 2, 2 of the emitters 11, 11 of adjacent unit transistors are, in this example, one common semi-insulating semiconductor layer 9.
1, the air bridge bottom portion 23 joined to the heat radiating plate of the air bridge metal conductor 2 extending from both the emitters 11 and 11 and the metal heat radiating plate 3 form a slot 24 cut out in the thickness direction. Thus, the two emitters 11 are electrically insulated by the semi-insulating semiconductor layer 91.

In this embodiment, as shown by arrows in the figure, the heat flow path from the emitter electrode 11 passes through the air bridge metal conductor 2, the heat sink 3, and the semi-insulating semiconductor layer 91. The heat reaches the back metal layer 92 and is radiated from the back metal layer 92 to the outside of the device. In this heat flow path, there is no need to form an emitter ballast resistance layer 13 (see FIG. 8) between the emitter contact layer 12 and the emitter layer 10 as in the prior art, so that Joule heat generation and thermal resistance due to the ballast layer are avoided. Can be thermally advantageous.

Embodiment 2 This embodiment is shown in FIG.
As shown in (A), each of the emitter connection conductors 15 is assembled on the collective wiring 16 via the emitter ballast resistor 14 and connected to the ground pad 17 according to the first embodiment. The same as above, but using via holes 4 formed in the semi-insulating semiconductor layer 91 to radiate heat from the air bridge metal conductor 2 connected to the emitter electrode 1 via the semi-insulating semiconductor layer 91 It is. In this example, the via hole 4 has a long rectangular or oblong shape on the upper surface, and is close to the unit transistor 1 in the region of the heat sink 3,
In addition, they are arranged so as to be elongated in parallel along the longitudinal direction of the unit transistor 1.

In FIG. 2B, in this example, the via hole 4 is opened toward the upper side of the substrate 9, penetrates through the heat sink 3 and the surface insulating layer 31, and is perforated in the semi-insulating semiconductor layer 91. The bottom surface 42 is stopped near the back metal layer 92. The via hole 4 has an opening, an inner peripheral surface, and a bottom surface 42 covered with a metal conductor 41, is connected to the heat sink 3, and has a hollow inside.

The metal conductor 41 of the via hole 4 is usually formed of a plating alloy layer to ensure high thermal conductivity of the via hole 4. Then, a part of the semi-insulating semiconductor layer 91 is interposed between the bottom surface 42 of the via hole and the back surface metal layer 92 while leaving a part of the semi-insulating semiconductor layer 91 as a thin insulating layer 32, so as to be thermally conductive and electrically insulating. Have been. In this embodiment, via holes 4 and unit transistors 1 are alternately arranged, and each via hole 4 is shared by heat flow paths of two adjacent unit transistors 1, but extends from two emitter electrodes. Air bridge metal conductor 2,2
The space is electrically insulated on the surface insulating layer 31 by a slot 24 formed by cutting the heat sink 3.

In the heat flow path having such a configuration, since the heat conduction of the via hole 4 is high, the heat flow rate of the entire heat flow path is increased,
The ability to dissipate heat from the emitter electrode 11 side to the back metal layer 92 can be enhanced, and at the same time, the emitter electrode 1 is electrically floated from the back metal layer 92 with the thin insulating layer 32 interposed.

Embodiment Embodiment 2 of the present invention. FIGS. 3 and 4 show modified examples of the via hole and its insulating method. In each case, the via hole 4 is opened upward from the substrate, and the heat sink 3 and the surface insulating layer 31 are semi-insulated. A through hole 40 penetrating through the conductive semiconductor layer 91 is provided, the opening, the inner peripheral surface, and the bottom surface 42 are covered with a metal conductor 41 and connected to the heat sink 3. In this example, a solder alloy is used for the metal conductor 41. Further, intermediate insulating layers 33 and 34 are interposed between the bottom surface 42 and the back surface metal layer 92, and are in a thermally conductive state but electrically insulated. Intermediate insulating layer 33,
Preferably, an SiON film is used for the thin film 34, and the thinner it is, the more preferable it is. The back metal layer is formed by forming the above-mentioned Ni / Au layer with a thickness of about 5000 °.

FIG. 3 shows a structure in which an intermediate insulating layer 33 is applied to the entire rear surface of the substrate 9 and a rear metal layer is formed on the entire surface of the intermediate insulating layer 33. FIG. 4 shows an example in which the intermediate insulating layer 34 is provided so as to be in contact with the back metal layer of the substrate 9 and to cover the bottom surface 42 of the via hole 4. In each case, the bottom surface 4 of the via hole 4
Numeral 2 comes into contact with the intermediate insulating layers 33 and 34 and stops, thereby ensuring heat conduction between the via hole 4 and the back metal layer 92 and electrical insulation by the intermediate insulating layer 33. 3 and FIG. 4, similarly, the adjacent emitter electrodes 11, 11 form a slot 24 in the air bridge metal conductor 2 and the radiator plate 3, and electrically connect via the surface insulating layer 31. Electrically insulated.

Embodiment 3 The next embodiment is described in the second embodiment. 5A, the via hole 4 is used, but as shown in FIGS. 5A and 5B, the via hole 4 is used.
Is opened on the back surface side of the substrate 9, penetrates the back metal layer 92, is perforated in the semi-insulating semiconductor layer 91,
Stop near the surface insulating layer 31 and the heat sink 3. The via hole 4 has an opening, an inner peripheral surface, and a bottom surface 42 covered with a metal conductor 41, is connected to the back metal layer 92, and has a hollow inside. In this example, as shown in FIG. 5D, the via holes 4 are arranged so as to extend close to the unit transistors 1 in the region of the heat sink 3 and extend in parallel along the longitudinal direction of the unit transistors 1. Are located in

The metal conductor 41 of the via hole 4 is usually formed of a plating alloy layer to ensure the heat conduction of the via hole 4. And the bottom 4 of the via hole
A part of the semi-insulating semiconductor layer 91 is left as a thin substrate insulating layer 32 and a surface insulating layer 31 is interposed between the heat insulating plate 2 and the heatsink, so that heat conduction and electrical insulation are achieved. I have.
Since the via hole 4 is formed by drilling from the back side, there is an advantage that the via hole can be easily formed. Also in this embodiment, between the emitter electrodes 11, 11 of the adjacent unit transistors 1, 1, an air bridge conductor 2 extending from each emitter electrode and a heat radiating plate 3 contacting the air bridge conductor 2 are provided with slots 214 to separate them. , Are electrically insulated by the surface insulating layer 31.

Embodiment Embodiment 3 of the present invention. 6 and 7 show a modified example of the via hole and its insulating method. In each case, the via hole 4 is opened toward the back surface of the substrate, and the back metal layer 92 and the semi-insulating semiconductor layer are formed. A through hole 40 is provided to penetrate through the opening 91, the opening, the inner peripheral surface and the bottom surface 42 are covered with the metal conductor 41, and the opening is connected to the back metal layer 92. Also in this example, a solder alloy is used for the metal conductor 41. Further, between the bottom surface 42 and the heat sink 3,
The surface insulating layer 31 or the intermediate insulating layer 34 is interposed and is thermally conductive but electrically insulated.

The surface insulating layer 31 and the smoke-saving film 34 are made of SiO ₂
A layer or, preferably, a SiON film is used, and the thinner the better, for example, about 1000 ° is employed. The back metal layer is formed of a Ni / Au layer having a thickness of about 5000 °, and is connected to the via hole 4 at an opening thereof.

FIG. 6 shows that the surface insulating layer 31 formed on the upper surface of the substrate is used as it is. FIG. 7 shows an example in which the intermediate insulating layer 34 is provided so as to be in contact with the heat sink 3 and to cover the bottom surface 42 of the via hole 4. In each case, the bottom surface 4 of the via hole 4
2 stops in contact with the surface insulating layer 31 or the intermediate insulating layer 34, and secures heat conduction between the via hole 4 and the heat sink 3 by the surface insulating layer 31 or the intermediate insulating layer 34; I'm trying.

[0039]

According to the bipolar transistor device of the present invention, an emitter ballast resistor is provided for each connection conductor from each emitter electrode of the unit bipolar transistor to the collective wiring, and the back metal of the substrate is provided from the emitter electrode of each unit bipolar transistor. Since the heat flow path leading to the layer is provided, the heat flow path is separated from the current path, and a ballast resistor is provided at the emitter of the current path to stabilize the operation of each unit bipolar transistor. Can dissipate heat.

Further, in the present invention, since the ballast resistor is a metal thin film formed on the substrate by being arranged in series with the electric wiring path of each emitter electrode, an appropriate resistance value is set and adjusted as the ballast resistor. This is effective for stabilizing each unit transistor.

The bipolar transistor device of the present invention
Since the heat flow path includes an air bridge conductor connected to the emitter electrode, a semi-insulating semiconductor layer, and a metal layer on the back surface of the substrate, the emitter electrode secures a path for heat dissipation on the back surface side of the substrate, and the bipolar transistor device has Effective for heat dissipation.

The bipolar transistor device of the present invention
The heat flow path includes a heat radiating plate formed on the substrate and connected to the air bridge conductor, and the heat radiating plate radiates heat to the semi-insulating semiconductor layer, so that a heat radiating area can be secured on the back surface of the substrate.

Further, since the heat flow path includes a via hole thermally connected to the air bridge conductor and the back metal layer of the substrate and inserted into the semi-insulating semiconductor layer, the heat flow along the via hole Can be secured.

The bipolar transistor device of the present invention
If the via hole is opened on the upper surface side of the substrate and connected to an air bridge conductor or a heat sink, and the bottom portion of the via hole is electrically insulated and thermally connected to the metal layer on the back surface of the substrate, The emitter of the transistor is electrically insulated from the backside metal layer of the substrate. Furthermore, the bottom of the via hole can be stopped in the semi-insulating semiconductor layer in contact with the substrate back metal layer, and penetrates the semi-insulating semiconductor layer, and the bottom contacts the substrate back metal layer. It can be stopped at a separate insulating layer, so that insulation can be ensured without obstructing the heat flow. In particular, if the insulating layer is a SiON film deposited on the back surface of the substrate, the insulating layer is extremely thin, and can hinder the heat flow.

The bipolar transistor device of the present invention
Since the via hole is opened from the back side of the substrate and connected to the back metal layer, and the bottom of the via hole is electrically insulated and thermally connected to an air bridge conductor or a heat sink on the substrate, The emitter of the unit transistor is electrically insulated from the backside metal layer of the substrate. Furthermore, the bottom of the via hole is stopped in the semi-insulating semiconductor layer that is in direct contact with the radiator plate or via the insulating layer, or the bottom of the via hole penetrates the semi-insulating semiconductor layer. By stopping at a separate insulating layer in contact with the heat sink, insulation can be ensured without obstructing the heat flow. In particular, the insulating layer may be a SiO 2 deposited on the backside of the substrate.
If an N film is used, it is possible to reduce the hindrance of heat flow with an extremely thin insulating layer.

[Brief description of the drawings]

FIG. 1 is a partial top view (A) and a partial cross-sectional view (B) of a bipolar transistor device according to an embodiment of the present invention.

FIG. 2 is a view similar to FIG. 1 of a bipolar transistor device according to another embodiment of the present invention, showing a device having via holes.

FIG. 3 is a partial cross-sectional view of a bipolar transistor device according to another example of the embodiment of the present invention.

FIG. 4 is a diagram similar to FIG. 3 of a bipolar transistor device according to another example of the embodiment of the present invention.

FIG. 5 is a view similar to FIG. 2 of a bipolar transistor device according to another embodiment of the present invention, showing a device having another form of via hole;

FIG. 6 is a partial cross-sectional view of a bipolar transistor device according to another example of the embodiment of the present invention.

FIG. 7 is a view similar to FIG. 6, showing a bipolar transistor device according to another example of the embodiment of the present invention;

FIG. 8 is a partial top view (A) and a partial cross-sectional view (B, C) of a conventional bipolar transistor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Unit bipolar transistor device 10 Emitter layer 11 Emitter electrode 14 Ballast resistor 2 Air bridge conductor 3 Heat sink 33 Intermediate insulating layer 4 Via hole 40 Bottom 7 Base electrode 8 Collector electrode 9 Semiconductor substrate 91 Semi-insulating semiconductor layer 92 Substrate backside metal layer

Claims (13)

[Claims] In a bipolar transistor device in which a number of unit bipolar transistors are arranged in a finger shape on a substrate, a ballast resistor for an emitter is provided on each connection conductor from each emitter electrode of each unit bipolar transistor to a collective wiring. A bipolar transistor device comprising a heat flow path from the emitter electrode of each unit bipolar transistor to a metal layer on the back surface of a substrate. 2. The bipolar transistor device according to claim 1, wherein the ballast resistor is a metal thin film formed on a substrate by being arranged in series with an electric wiring path of each emitter electrode. 3. An air bridge conductor having a heat flow path connected to the emitter electrode, a semi-insulating semiconductor layer of a substrate thermally connected to the air bridge conductor, and a substrate joined to the semi-insulating semiconductor layer. 3. The bipolar transistor device according to claim 1, comprising a back metal layer, wherein the emitter electrode and the back metal layer are electrically insulated. 4. The bipolar transistor according to claim 3, wherein the heat flow path includes a heat sink formed on the substrate and connected to the air bridge metal conductor, and the heat sink radiates heat to the semi-insulating semiconductor layer. apparatus. 5. The bipolar transistor according to claim 3, wherein the heat flow path includes a via hole thermally connected to the air bridge conductor and the backside metal layer of the substrate and inserted into the semi-insulating semiconductor layer. Transistor device. 6. The via hole is opened on the upper surface side of the substrate and connected to an air bridge conductor or a heat sink.
6. The bipolar transistor device according to claim 5, wherein a bottom portion of the via hole is electrically insulated and thermally connected to a metal layer on the back surface of the substrate. 7. The bipolar transistor device according to claim 6, wherein the bottom of the via hole is stopped in the semi-insulating semiconductor layer in contact with the metal layer on the back surface of the substrate. 8. The bipolar transistor according to claim 6, wherein said via hole penetrates through said semi-insulating semiconductor layer, and a bottom portion thereof is stopped by a separate insulating layer in contact with a metal layer on the back surface of the substrate. apparatus. 9. The bipolar transistor device according to claim 8, wherein the insulating layer is a SiON film deposited on a back surface of the substrate. 10. The via hole is opened from the back side of the substrate and connected to the back metal layer, and the bottom of the via hole is electrically insulated and thermally connected to an air bridge conductor or a heat sink on the substrate. 6. The bipolar transistor device according to claim 5, wherein: 11. The bipolar transistor device according to claim 10, wherein the bottom of the via hole is stopped in the semi-insulating semiconductor layer which is in contact with the heat sink directly or via an insulating layer. 12. The bipolar transistor according to claim 10, wherein the bottom of the via hole penetrates the semi-insulating semiconductor layer, and the bottom is stopped at a separate insulating layer in contact with the heat sink. apparatus. 13. The bipolar transistor device according to claim 11, wherein said insulating layer is a SiO ₂ film or a SiON film deposited on a surface of a semi-insulating semiconductor layer of a substrate.