JP2007116007A - Semiconductor power amplifier and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor power amplifier and a method for manufacturing the same which offer both advantages of an improvement in an amplification gain (high output operation) and an improvement in a thermal runaway suppression effect (stable operation). <P>SOLUTION: The emitter of each HBT (heterojunction bipolar transistor) 40 is connected to an emitter (ground) terminal 3 via a first emitter ballast resistance 41 and a second emitter ballast resistance 42 connected in parallel. The first emitter ballast resistance 41 and the second emitter ballast resistance 42 are made of different materials having respective temperature characteristics such that a resistance change tendency accompanying a temperature change is reverse to each other between the first emitter ballast resistance 41 and the second emitter ballast resistance 42. As a result, the drawback of the first emitter ballast resistance 41 that a resistance decreases (or increases) as a temperature increases can be eased by the drawback of the second emitter ballast resistance 42 that a resistance increases (or decreases) as a temperature increases. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power amplifier using a transistor circuit. More specifically, the present invention is used in a signal transmission unit of a radio communication device using a high frequency band mainly of a mobile phone and has excellent high frequency power amplification characteristics as an active element. The present invention relates to a semiconductor power amplifier using a heterojunction bipolar transistor (HBT) and a manufacturing method thereof.

  In general, in semiconductors for high-frequency signal power amplifiers, small cell structures of HBTs made of gallium arsenide (GaAs) or silicon germanium (SiGe) having excellent high-frequency characteristics are connected in parallel (multi-cells). Thus, a circuit configuration is obtained in which the outputs of the transistors are combined to obtain a high output. The HBT generates heat when performing a high output operation because the current density of the alternating current per unit cell increases. Since this heat generation is not uniform due to the HBT, the HBT having a high temperature may further break down due to thermal runaway.

  Therefore, in order to suppress an excessive collector current that causes this thermal runaway, it is often performed to provide a resistance at the emitter of each HBT. This emitter resistance is generally called an emitter ballast resistor for uniformly and stably operating a multi-cell HBT.

FIG. 5 shows a conventional multi-cell HBT structure having an emitter ballast resistor (see Patent Document 1). An emitter ballast resistor 410 is provided on the emitter electrode of each HBT 400. With this structure, the HBT cell that generates more heat than the periphery operates with the collector ballast resistor 410 suppressing the collector current and without causing thermal runaway.
JP 2001-168107 A

  However, this emitter ballast resistor has the following problems. If the resistance value of the emitter ballast resistor is excessive, a power loss occurs when a collector current necessary for outputting power flows, so that the amplification gain decreases. On the other hand, if the resistance value of the emitter ballast resistor is too small, the effect of suppressing thermal runaway is lacking. That is, there is a trade-off relationship between suppressing a decrease in amplification gain and suppressing thermal runaway, and it is a problem that it is difficult to achieve both.

  For this reason, a method of suppressing the base current supplied from the bias circuit by inserting a resistor called a so-called base ballast resistor on the base side of the transistor is often used recently. However, there is a similar problem in the method of inserting the base ballast resistor. In other words, since the base current is a small amount, a large resistance value is required to increase the thermal runaway suppression effect. However, the current supply capability from the bias circuit is not degraded, in other words, the amplification gain is not decreased. Is a problem that requires a small resistance value.

  Further, a conventional technique for realizing an emitter ballast resistor is to form a high resistance layer on an emitter layer of an HBT by epitaxial growth and use the formed high resistance layer as an emitter ballast resistor. However, since this emitter ballast resistor is composed of a semiconductor layer, the resistance value decreases as the temperature rises. Therefore, when the temperature rises due to heat generation when the amplifier has a high output, there is a problem that the effect of the emitter ballast resistor on the thermal runaway is suppressed.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a semiconductor power amplifier and a method for manufacturing the same, in which an improvement in amplification gain (high output operation) and an improvement in thermal runaway suppression effect (stable operation) that are in a trade-off relationship are achieved. It is to be.

  The present invention is directed to a semiconductor power amplifier configured by connecting a plurality of cell circuits for performing power amplification in parallel. In order to achieve the above object, the cell circuit constituting the semiconductor power amplifier of the present invention is connected between a transistor that amplifies and outputs a signal input to the base from the collector, and the emitter of the transistor and the ground. And a second emitter ballast resistor connected in parallel with the first emitter ballast resistor between the emitter of the transistor and the ground. In addition, the first emitter ballast resistor and the second emitter ballast resistor are set to temperature characteristics in which the tendency of change in resistance value due to temperature change is contradictory.

  For example, when the first emitter ballast resistor has a temperature characteristic that the resistance value decreases as the temperature rises, the second emitter ballast resistor is set to have a temperature characteristic that the resistance value increases as the temperature rises. . In this case, the first emitter ballast resistor is typically made of a semiconductor material and the second emitter ballast resistor is typically made of a metal material. The first emitter ballast resistor is preferably formed using a sub-collector layer of a transistor formed on a semiconductor substrate.

  When this semiconductor power amplifier is formed on a semiconductor substrate, the first and second emitter ballast resistors can be manufactured by forming collector electrodes in the subcollector layer of the transistor region and at the same time, Collector electrodes are provided at both ends of the sub-collector layer formed to form a first emitter ballast resistor, thin film metal is evaporated in parallel with the formed first emitter ballast resistor, An emitter ballast resistor is preferably formed.

  As described above, according to the present invention, the emitter ballast resistor of the transistor is composed of a combined resistor composed of two resistors having temperature characteristics in which the tendency of change in resistance value with temperature change is contradictory. As a result, the two resistors change so as to compensate for the disadvantages of the temperature characteristics of each, so that the temperature dependence of the combined resistor can be reduced and the thermal runaway region of the transistor can be avoided. .

  FIG. 1 is a circuit diagram showing a configuration of a semiconductor power amplifier according to an embodiment of the present invention. As shown in FIG. 1, the semiconductor power amplifier of the present invention has a structure in which a plurality of unit HBT structures 10 are connected in parallel. The unit HBT structure 10 includes an HBT 40, a first emitter ballast resistor 41, and a second emitter ballast resistor 42. The collector and base of each HBT 40 are commonly connected to the collector terminal 2 and the base terminal 1, respectively. The emitter of each HBT 40 is connected to the emitter (ground) terminal 3 via a first emitter ballast resistor 41 and a second emitter ballast resistor 42 connected in parallel.

  In the present embodiment, the configuration of the semiconductor power amplifier using the HBT 40 will be described, but a configuration using a general transistor may be used. In the present embodiment, a configuration in which four unit HBT structures 10 are connected in parallel will be described, but the number of units to be connected is not limited to four, and may be any number.

  The first emitter ballast resistor 41 and the second emitter ballast resistor 42 are formed of a material having temperature characteristics in which the tendency of change in resistance value with temperature change is contradictory. Typically, the first emitter ballast resistor 41 is made of a semiconductor material, and the second emitter ballast resistor 42 is made of a metal material. Note that although the metal material has a low resistivity, it is possible to form a resistor of about several Ω by using a thin film metal.

FIG. 2 is a diagram showing an example of temperature characteristics of the first emitter ballast resistor 41 made of a semiconductor material and the second emitter ballast resistor 42 made of a metal material.
The first emitter ballast resistor 41 formed of a semiconductor material exhibits a temperature characteristic in which the resistance value R decreases exponentially as the temperature T increases, as shown by the dotted line in FIG. This logarithmic characteristic is a function of 1 / T when expressed in logarithm, and its coefficient is proportional to the energy band gap. On the other hand, the second emitter ballast resistor 42 formed of a metal material exhibits a temperature characteristic in which the resistance value R changes in a linear function as the temperature T rises, as shown by a one-dot chain line in FIG.

  Therefore, by connecting the first emitter ballast resistor 41 and the second emitter ballast resistor 42 in parallel, the resistance value decreases as the temperature of the semiconductor material of the first emitter ballast resistor 41 increases. This disadvantage can be mitigated by the disadvantage that the resistance value increases as the temperature of the metal material of the second emitter ballast resistor 42 increases. Therefore, the combined resistance value of the first emitter ballast resistor 41 and the second emitter ballast resistor 42 has a small temperature dependency as shown by the solid line in FIG.

Next, a structure and a manufacturing method for realizing the semiconductor power amplifier of the present invention having the above-described configuration on a semiconductor substrate will be described with specific examples.
FIG. 3A is a top view of a semiconductor power amplifier according to an embodiment of the present invention formed on a semi-insulating semiconductor substrate. 3B is a cross-sectional view taken along the line aa in FIG. 3A. 4A and 4B are a top view and a cross-sectional view for explaining a procedure for manufacturing the semiconductor power amplifier shown in FIGS. 3A and 3B.

First, the structure of the HBT 40 will be described with reference to FIGS. 3A and 3B.
The emitter electrode 31 is formed on the emitter layer 34, and the base electrode 32 is formed on the base layer 35, respectively. The collector electrode 33 is formed on the subcollector layer 37 that serves as a contact layer for the collector layer 36. The emitter layer 34 and the collector layer 36 are made of n-type GaAs, and the base layer 35 is made of p-type GaAs. Since the subcollector layer 37 is a contact layer, it is made of n-type GaAs having a higher concentration than the collector layer 36. In order to realize ohmic contact with respect to the emitter layer 34, an InGaAs layer is inserted at the junction surface with the emitter electrode 31, and an InGaP layer having a wider band gap than GaAs is inserted at the matching surface with the base layer 35. . Thereby, a heterojunction surface is formed. The emitter electrode 31 is WSi, the base electrode 32 is an alloy of Ti, Pt, and Au, and the collector electrode 33 is an alloy of AuGe, Ni, and Au.

Next, the structure of each emitter ballast resistor will be described with reference to FIGS. 3A and 3B.
A first emitter ballast resistor 41 using the subcollector layer 37 and a second emitter ballast resistor 42 using a thin film metal are formed on the semi-insulating semiconductor substrate 50. The emitter electrode 31 and one end of the first emitter ballast resistor 41 and the second emitter ballast resistor 42 are connected by a wiring A, and the other end is connected by a wiring B to a grounded via hole 43. The The first emitter ballast resistor 41 uses a sheet resistance of about 10Ω of the high concentration sub-collector layer 37 of about 10 ¹⁸ cm ⁻³ . A collector electrode 33 is provided at both ends as shown in FIG. This is used as two terminals of the first emitter ballast resistor 41. The second emitter ballast resistor 42 is formed using Au thin film metal having a thickness of about 150 nm. By setting the ratio of the width to the length of the thin film metal to about 15, a resistance value of several Ω can be obtained.

Next, a method for manufacturing a semiconductor power amplifier will be described with reference to FIGS. 4A and 4B.
First, etching and electrode formation of an epitaxially grown semiconductor substrate are performed by a general manufacturing method. An emitter electrode 31 and a base electrode 32 are formed on an emitter layer 34 and a base layer 35, respectively. To expose. See steps (A1) and (B1).

  Next, an inactivated element isolation region 38 is formed by implanting ions such as He. At this time, the region 45 for forming the first emitter ballast resistor 41 is formed at the same time. See steps (A2) and (B2).

  Next, the collector layer 36 is etched to expose the subcollector layer 37, and the collector electrode 33 is formed by vapor deposition. Here, when the collector electrode 33 in the HBT region is formed, the first emitter ballast resistor 41 is formed by simultaneously forming the collector electrode 33 at both ends of the emitter ballast resistor region 45. See steps (A3) and (B3).

  Next, a second emitter ballast resistor 42 is formed by depositing a thin film metal in parallel with the first emitter ballast resistor 41. See steps (A4) and (B4). By this step, a composite emitter ballast resistor in which the first emitter ballast resistor 41 and the second emitter ballast resistor 42 are connected in parallel is formed.

  Finally, the emitter electrode 31 of the HBT 40 and one end of the first emitter ballast resistor 41 and the second emitter ballast resistor 42 are connected by the wiring A. The other ends of the first emitter ballast resistor 41 and the second emitter ballast resistor 42 are connected to a grounded via hole 43 by a wiring B. See steps (A5) and (B5). Thereby, the semiconductor power amplifier of the present invention having the above-described configuration is formed.

  As described above, according to the semiconductor power amplifier according to the embodiment of the present invention, the emitter ballast resistor of the HBT is formed by the two resistors having temperature characteristics in which the change tendency of the resistance value with the temperature change is contradictory. It is composed of a composite resistor. As a result, the two resistors change so as to compensate for the disadvantages of the temperature characteristics of each, so that the temperature dependence of the combined resistor can be reduced and the thermal runaway region of the HBT can be avoided. .

  The semiconductor power amplifier and the manufacturing method thereof according to the present invention can be used for a signal transmission unit or the like of a radio communication device using a high frequency band mainly of a mobile phone, and particularly when both high output operation and stable operation are desired. Suitable for etc.

1 is a circuit diagram showing a configuration of a semiconductor power amplifier according to an embodiment of the present invention. Diagram showing an example of temperature characteristics of emitter ballast resistor 1 is a top view of a semiconductor power amplifier according to an embodiment of the present invention. Sectional drawing of the semiconductor power amplifier which concerns on one Embodiment of this invention The top view for demonstrating the manufacturing method of the semiconductor power amplifier which concerns on one Embodiment of this invention. Sectional drawing for demonstrating the manufacturing method of the semiconductor power amplifier which concerns on one Embodiment of this invention. Circuit diagram showing the configuration of a conventional semiconductor power amplifier

Explanation of symbols

1-3 Terminal 10 Unit HBT structure 31 Emitter electrode 32 Base electrode 33 Collector electrode 34 Emitter layer 35 Base layer 36 Collector layer 37 Subcollector layer 40 Heterojunction bipolar transistor (HBT)
41, 42 Emitter ballast resistor 43 Via hole 50 Semi-insulating semiconductor substrate

Claims (5)

A semiconductor power amplifier configured by connecting a plurality of cell circuits for performing power amplification in parallel,
The cell circuit is
A transistor that amplifies and outputs a signal input to the base from the collector;
A first emitter ballast resistor connected between the emitter of the transistor and ground;
A second emitter ballast resistor connected in parallel with the first emitter ballast resistor between the emitter of the transistor and ground;
2. The semiconductor power amplifier according to claim 1, wherein the first emitter ballast resistor and the second emitter ballast resistor are set to temperature characteristics in which the tendency of change in resistance value accompanying temperature change is contradictory.   The first emitter ballast resistor has a temperature characteristic in which a resistance value decreases as the temperature rises, and the second emitter ballast resistor has a temperature characteristic in which a resistance value increases as the temperature rises. The semiconductor power amplifier according to claim 1.   3. The semiconductor power amplifier according to claim 2, wherein the first emitter ballast resistor is made of a semiconductor material, and the second emitter ballast resistor is made of a metal material.   4. The semiconductor power amplifier according to claim 3, wherein the first emitter ballast resistor is formed using a sub-collector layer of the transistor formed on a semiconductor substrate. On a semiconductor substrate, first and second emitter ballast resistors that are connected in parallel between the emitter of a transistor and ground and have temperature characteristics in which the tendency of change in resistance value due to temperature change are contradictory are manufactured. A method,
Forming a collector electrode on the sub-collector layer in the transistor region, and simultaneously forming collector electrodes on both ends of the activated sub-collector layer other than the transistor region to form the first emitter ballast resistor;
A method of forming a second emitter ballast resistor by depositing a thin film metal in parallel with the first emitter ballast resistor formed by the step.

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