The present invention relates to a semiconductor integrated circuit device in which a semiconductor power device used to achieve a high breakdown voltage and a large electric current is disposed and to equipment for a communication system which uses the semiconductor power device such as a mobile terminal or a radio base station.
A silicon carbide (SiC) having a larger band gap than silicon (Si) is a semiconductor which is high in breakdown voltage and stable even at a high temperature and is termed a power diode, a power transistor, or the like. Accordingly, an active element formed by using a SiC substrate is expected to be applied to a next-generation power device or high-temperature operating device.
In general, a power device is a generic name for a device which converts or controls high power. Exemplary applications of the power device include mobile terminal equipment functioning as a mobile station in a communication system, a car phone, or a transistor or diode disposed at a base station therein. The applications of the power device are expected to be widened in the future.
A typical modular structure used for such applications is obtained by connecting a plurality of semiconductor chips each having a power device embedded therein with wires in accordance with a use or an object and placing the connected semiconductor chips in a single package. For example, a desired circuit is constructed with semiconductor chips and wires by forming the wires on a substrate such that a circuit suitable for the use is constructed and mounting the individual semiconductor chips on the substrate. A description will be given herein below to a transmitting/receiving circuit at a radio base station which uses a Schottky diode and a MOSFET.
FIG. 20 is a block circuit diagram showing an internal structure of a conventional base station (base station in a communication system) disclosed in a document (Daisuke Ueda et al., “Radio-Frequency and optical Semiconductor Devices Exploring New Age of Data Communication,” IEICE, Dec. 1, 1999, p.124). As shown in the drawing, the circuit comprises an antenna main body, a switch, a received-signal amplifier, an amplified-signal transmitter, a radio transmitter/receiver, a baseband signal processor, an interface unit, an exchange controller, a controller, and a power supply portion. The received-signal amplifier is composed of two filters and two low-noise amplifiers (LNA) disposed in series. A mixer for mixing an output from a local amplifier with an output from an RF emitter to generate an RF signal is disposed in the radio transmitter/receiver. A power dividing/synthesizing circuit having a driver amplifier, a filter, a middle amplifier, and a main amplifier disposed therein is disposed in the amplified-signal transmitter. There are further provided a baseband signal processor for processing an audio signal, an interface unit, and an exchange controller connected to a network.
At the conventional base station, the main amplifier is so configured as to perform impedance matching by disposing an input matching circuit and a field-effect transistor (MESFET) formed by using a GaAs substrate, while disposing a capacitor, an inductor, and a resistor element on each of the input side and output side.
A MOSFET formed on a silicon substrate, a diode, a capacitor, a resistor element, and the like are disposed in the controller, the baseband signal processor, the interface unit, and the exchange controller. Such parts as a capacitor and an inductor which occupy a particularly large area are formed as independent chips.
However, the foregoing conventional communication system has the following disadvantages.
At the conventional base station, the signal amplifying elements which are the most important parts of the transmitting/receiving circuit are generally formed by using the GaAs substrate. Since the heat resistance of GaAs is low, a cooling device having a high cooling ability is required to suppress a temperature rise, so that high running cost is required to maintain the base station. If the transmitting/receiving circuit is to be applied to a mobile terminal, the circuit should be scaled down. However, there are strict positional constraints such that a GaAs MESFET and the like having a low heat resistance should be positioned at a distance from a FET and an inductor of which temperatures are easily increased by an RF signal. As a result, the transmitting/receiving circuit itself is inevitably increased in size despite various considerations given to the positional relations among the individual parts.
In addition, the signal amplifying elements which are the most important parts of the transmitting/receiving circuit and the like are provided by disposing a large number of MESFETs at a portion at which a particularly large power should be amplified. As the frequency of the RF signal is higher, however, reflected waves from the MESFETs exert multiple effects so that it is difficult to achieve impedance matching. This causes the disadvantage of increased labor required by trimming for impedance adjustment.