JP2006147665A - Transistor semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transistor semiconductor device which can prevent the thermal runaway of a transistor without using a ballast resistor. <P>SOLUTION: The transistor Tr1 of an amplifier circuit 10 and diodes D1 and D2 of a bias circuit 20 are all arranged on one and the same semiconductor substrate, and covered with heat conduction wiring 30 formed of a metal material, etc. having good heat conduction. A rise in temperature which occurs in the transistor Tr1 can be rapidly transmitted to the diodes D1 and D2 by means of the heat conduction wiring 30. Since the diodes D1 and D2 operate in the direction of decreasing the temperature of the transistor Tr1, the thermal runaway of the transistor Tr1 can be prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transistor semiconductor device, and more particularly to a structure of a transistor semiconductor device that prevents the occurrence of a thermal runaway phenomenon of a transistor (such as a bipolar transistor) due to a temperature rise.

In recent years, with increasing demand for mobile communication devices such as mobile phones, semiconductor devices used for power amplifiers and the like of communication devices are also diversifying. In particular, bipolar transistors have the following advantages over field effect transistors (FETs).
1. Since a negative power supply is not necessary in principle, a regulator for generating a negative voltage is not required (single power supply operation).
2. Since the collector current can be cut off by setting the base current to zero, a power switch for turning on / off the amplifier power supply is unnecessary.

  Due to these advantages, bipolar transistors have been increasingly used in recent years. Also, since mobile communication devices generally use high frequencies of 1 GHz to 6 GHz, heterojunction bipolar transistors (HBT) using gallium arsenide (GaAs) as a semiconductor substrate are used for these power amplifiers.

  However, the bipolar transistor has a demerit that it tends to cause thermal runaway as compared with the FET due to the characteristics of the device, and causes element destruction. The mechanism by which the element is destroyed due to thermal runaway will be described below.

5 and 6 are diagrams for explaining the mechanism of thermal runaway in a conventional bipolar transistor.
In FIG. 5, a base power source 102 is connected to the base of the bipolar transistor Tr101, and a collector power source 103 is connected to the collector. When base voltage (= base-emitter voltage) is Vbe, base current is Ib, collector voltage (= collector-emitter voltage) is Vce, collector current is Ic, and saturation current is Is, The formula holds. In addition, when temperature T = 300K, it is q / kT-38.7.
Ic = Is × exp ((q / kT) × Vbe)

FIG. 6 is a diagram illustrating the VI characteristic of the collector current Ic with respect to the base voltage Vbe in the equivalent circuit of FIG. In FIG. 6, the element temperature of the transistor increases in the order of IV1 (solid line) <IV2 (dotted line) <IV3 (dashed line).
In general, in a Si bipolar transistor, when the collector current Ic is kept constant, the base voltage Vbe exhibits a temperature coefficient of about −2 mV / ° C. Therefore, conversely, when the element temperature of the transistor is raised while keeping the base voltage Vbe constant, the collector current Ic increases (transition of Ic1 → Ic2 and Ic2 → Ic3 in FIG. 6). This increase in the collector current Ic further increases the element temperature of the transistor, and a positive feedback vicious cycle of increasing the collector current Ic → increasing the element temperature of the transistor → increasing the collector current Ic → increasing the element temperature of the transistor. produce. When the collector current Ic exceeds the allowable loss of the transistor element, the element is thermally destroyed. This is the mechanism of thermal runaway occurrence.

A conventional transistor circuit including a bias circuit for controlling the base voltage Vbe to be constant is disclosed in Patent Document 1, Patent Document 2, and the like.
JP 2001-274636 A JP 2003-347850 A

  One technique for suppressing this thermal runaway is to insert a ballast resistor in the base or emitter of the transistor. However, in this case, there is a problem that it is necessary to secure a region for forming a ballast resistor on the semiconductor substrate, and a problem that a gain characteristic for a high frequency signal is deteriorated by the ballast resistor.

  Therefore, an object of the present invention is to provide a transistor semiconductor device that can prevent thermal runaway of a transistor without using a ballast resistor.

  The present invention is directed to a transistor semiconductor device formed on a semiconductor substrate. In order to achieve the above object, the transistor semiconductor device of the present invention includes an amplifier circuit, a bias circuit, and a heat conduction wiring.

  An amplifier circuit is a circuit that includes at least a transistor that amplifies a signal input to a base and outputs the amplified signal to a collector. The bias circuit is a circuit that includes at least a temperature control element whose characteristics change with a temperature change, and supplies a bias voltage controlled by the temperature control element to the base of the transistor. The heat conduction wiring is a wiring for transmitting a temperature change of the transistor to the temperature control element.

Preferably, the heat conductive wiring is formed in an arrangement structure that covers at least a part of both the transistor and the temperature control element and electrically separates both. Further, the heat conduction wiring is electrically connected to either the collector electrode of the transistor or the temperature control element. Typically, a metal wiring formed in the semiconductor device manufacturing process is used for the heat conduction wiring. The heat conductive wiring may be directly electrically separated into the collector electrode and the temperature control element, but may be thermally coupled through an insulating film or the like.
For example, a PN junction diode or a thermistor may be used as the temperature control element.

  As described above, according to the present invention, negative feedback control is performed to lower the base voltage when the temperature of the transistor rises by feeding back the temperature change of the transistor to the bias circuit using the heat conductive wiring. As a result, it is possible to prevent the occurrence of transistor thermal runaway due to the positive feedback accompanying the temperature rise.

  A feature of the present invention resides in a semiconductor structure capable of preventing the occurrence of a thermal runaway phenomenon due to a temperature rise of a transistor without using a special circuit configuration. Hereinafter, a transistor semiconductor device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an equivalent circuit diagram of a transistor semiconductor device according to an embodiment of the present invention. In FIG. 1, the transistor semiconductor device according to this embodiment includes an amplifier circuit 10 that amplifies and outputs an input signal, and a bias circuit 20 that supplies a bias voltage to the amplifier circuit 10.

  The amplifier circuit 10 is a signal amplifying transistor Tr1, a choke resistor R1, a resistor R2 connecting the bias circuit 20 and the base of the transistor Tr1, a capacitor C1 as an input side coupling capacitor, and an output side coupling capacitor. The capacitor C2. The bias circuit 20 includes a transistor Tr2 for a bias circuit, PN junction diodes D1 and D2 that function as temperature control elements, a resistor R3, and a resistor R4. The transistors Tr1 and Tr2 are typically bipolar transistors or heterojunction bipolar transistors.

  In the bias circuit 20, the base of the transistor Tr2 is connected to the power supply Vbb via the resistor R4, and is connected (grounded) to the GND via the diode D1 and the diode D2 connected in series. The collector of the transistor Tr2 is connected to the power supply Vbb. The emitter of the transistor Tr2 is connected to the GND via the resistor R3, and is connected to the base of the transistor Tr1 of the amplifier circuit 10 via the resistor 2.

  In the amplifier circuit 10, the input signal (IN) is input to the base of the transistor Tr1 via the capacitor C1 and the bias voltage supplied from the bias circuit 20 via the resistor R2. The emitter of the transistor Tr1 is connected to GND. The collector of the transistor Tr1 is connected to the power source Vcc via the resistor R1, and outputs an amplified signal appearing at the collector via the capacitor C2 (OUT).

  On the equivalent circuit diagram, there is no particular difference between the present invention and the prior art. A feature of the present invention is a structure (temperature conduction structure) when this equivalent circuit is formed on a semiconductor substrate, and a bias control method utilizing the structure.

  FIG. 2 is a top view of a transistor semiconductor device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of the transistor semiconductor device shown in FIG. As shown in FIGS. 2 and 3, in the present invention, it is conventional that a heat conductive wiring 30 is newly provided for transmitting the temperature of the transistor Tr <b> 1 of the amplifier circuit 10 to the diode D <b> 1 and the diode D <b> 2 of the bias circuit 20. And different. The heat conduction wiring 30 may be a wiring formed of a material (for example, metal) having excellent heat conduction performance that can transmit the temperature of the transistor Tr1 that is a heat source to the diode D1 and the diode D2 that are temperature control elements. . The heat conduction wiring 30 is electrically connected to the collector of the transistor Tr1 so that the temperature of the transistor Tr1 can be extracted efficiently. On the other hand, the heat conductive wiring 30 is electrically separated from the diode D1 and the diode D2 by a protective film (for example, an insulating layer). That is, the diode D1 and the diode D2 are covered with the heat conductive wiring 30. Note that the terminal of the transistor Tr1 connected to the heat conductive wiring 30 may be an emitter or a base other than the collector.

A mechanism capable of preventing thermal runaway of the transistor Tr1 by using the semiconductor structure will be described.
First, in the bias circuit 20, assuming that the base current flowing into the transistor Tr2 is very small, the current flowing through the resistor R4 is equal to the current flowing through the diode D1 and the diode D2. This current is Ibias. The base voltage of the transistor Tr2 is Vbias1, and the emitter voltage is Vbias2. FIG. 4 shows the IV characteristics of the diode D1 and the diode D2. The base voltage Vbias1 of the transistor Tr2 is obtained from the intersection of the diode D1 and the IV characteristic line of the diode D2 by subtracting the load line of the resistor R4 from the power supply Vbb. As described in the prior art, since each diode has a temperature characteristic of −2 mV / ° C., the diode D1 + diode D2 circuit exhibits an IV characteristic of −4 mV / ° C. Therefore, the IV characteristic (one-dot chain line) at a high temperature shifts to the left side in FIG. 4 more than the IV characteristic (solid line) at a normal temperature. This means that the drop potential (collector-emitter potential) of the diode D1 and the diode D2 decreases as the temperature rises.

  Consider the case where the temperature of the transistor Tr1 rises and the collector current Ic increases. The increased temperature of the transistor Tr1 is also transmitted to the diode D1 and the diode D2 via the heat conduction wiring 30. That is, the temperature of the diode D1 and the diode D2 also increases in proportion to the temperature of the transistor Tr1. Due to the temperature rise of the diode D1 and the diode D2, the IV characteristic shifts from a solid line to a one-dot chain line (see FIG. 4), so that the base voltage Vbias1 (high temperature) is lower than the base voltage Vbias1 (normal temperature). Since the transistor Tr2 operates as an emitter follower, the emitter voltage Vbias2 (high temperature) is also lower than Vbias2 (normal temperature).

  As the emitter voltage Vbias2 of the transistor Tr2 decreases, the bias voltage applied to the base of the transistor Tr1, that is, the base voltage also decreases. As a result, the base current Ib flowing into the base of the transistor Tr1 is decreased, that is, the collector current Ic is decreased. As a result, the temperature of the transistor Tr1 is decreased.

  As described above, according to the transistor semiconductor device of the embodiment of the present invention, the bias circuit itself has a general configuration, but the heat of the transistor Tr1 of the amplifier circuit is efficiently transferred using the heat conduction wiring. Feedback to the diodes D1 and D2 is performed to perform negative feedback control for lowering the base voltage when the temperature of the transistor rises. As a result, it is possible to prevent the occurrence of transistor thermal runaway due to the positive feedback accompanying the temperature rise.

  In order to effectively realize the present invention, it is necessary to promptly transmit the temperature rise of the transistor Tr1 that is a heat source to the diode D1 and the diode D2 that are temperature control elements. Therefore, it is preferable to use the thickest metal wiring formed in the semiconductor device manufacturing process as the heat conductive wiring 30. For example, when the wiring is composed of a first layer wiring of about several thousand A and a second layer wiring of several μm, the second layer wiring can be efficiently used as the heat conduction wiring 30. Heat can be conducted to the diode D1 and the diode D2.

In addition, if the transistor Tr1 and the diode D1 and the diode D2 are arranged at the shortest distance, the heat conduction wiring 30 can be shortened as much as possible, and it is needless to say that the temperature change is transmitted quickly and is more effective.
Furthermore, although the case where the diode D1 and the diode D2 are used as the temperature control element has been described in the above embodiment, the element has a function capable of decreasing the drop potential in inverse proportion to the temperature rise of the transistor Tr1. If present, the temperature control element is not limited to a diode. For example, a thermistor may be used as the temperature control element.

  The transistor semiconductor device of the present invention is useful for preventing the occurrence of a thermal runaway phenomenon caused by the temperature rise of a transistor.

1 is an equivalent circuit diagram of a transistor semiconductor device according to an embodiment of the present invention. 1 is a top view of a transistor semiconductor device according to an embodiment of the present invention. Sectional drawing of the transistor semiconductor device which concerns on one Embodiment of this invention The figure which shows the IV characteristic of the diode D1 and the diode D2 of the transistor semiconductor device which concerns on one Embodiment of this invention. Diagram showing a conventional transistor circuit The figure which shows the IV characteristic of the conventional transistor

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Amplifier circuit 20 Bias circuit 30 Thermal conduction wiring Tr1, Tr2, Tr101 Transistor R1-R4 Resistor C1, C2 Capacitor D1, D2 Diode Vbb, Vcc, 102, 103 Power supply

Claims (6)

A transistor semiconductor device formed on a semiconductor substrate,
An amplifier circuit including at least a transistor that amplifies a signal input to the base and outputs the amplified signal to the collector;
A bias circuit that includes at least a temperature control element whose characteristics change with a temperature change, and supplies a bias voltage controlled by the temperature control element to the base of the transistor;
A transistor semiconductor device comprising: heat conduction wiring for transmitting a temperature change of the transistor to the temperature control element.   2. The heat conduction wiring according to claim 1, wherein the heat conduction wiring covers at least a part of both the transistor and the temperature control element, and is formed in an arrangement structure in which both are electrically separated. Transistor semiconductor device.   The transistor semiconductor device according to claim 2, wherein the heat conductive wiring is electrically connected to a collector electrode of the transistor.   The transistor semiconductor device according to claim 1, wherein a metal wiring formed in a semiconductor device manufacturing process is used for the heat conductive wiring.   The transistor semiconductor device according to claim 1, wherein a PN junction diode is used for the temperature control element.   The thermistor is used for the said temperature control element, The transistor semiconductor device in any one of Claims 1-4 characterized by the above-mentioned.

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