Semiconductor power device for high-temperature applications

Details Semiconductor power device for high-temperature applications Semiconductor power device for high-temperature applications

2002-02-26

2004-01-06

Flynn, Nathan J. (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S124000, C257S476000, C257S516000, C257S528000, C257S531000, C257S532000, C438S105000, C438S931000, C438S957000

Reexamination Certificate

active

06674131

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a semiconductor power device for use in high-temperature applications requiring a high breakdown voltage and a large current, which is suited to high-power-consumption equipment such as a lighting device or an air conditioner.
BACKGROUND ART
Silicon carbide (SiC) is a semiconductor having a band gap larger than that of silicon (Si) and therefore high dielectric resistance. Since silicon carbide retains stability at high temperatures, a semiconductor device 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 and is termed a power diode, a power transistor, or the like. Exemplary applications of the power device include a transistor and a diode disposed in the inverter control unit of such equipment as a vacuum cleaner, a laundry washer, a refrigerator, a fluorescent lamp, or an air conditioner. The applications of the power device is expected to be widened in the future.
For these applications, a plurality of semiconductor chips are typically connected with wires in accordance with a use and an object and placed in a single package to provide a modular structure. 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. As a conventional example of a semiconductor power device circuit, a description will be given to an inverter circuit for a fluorescent lamp using a Schottky diode and a MOS field effect transistor.
FIG. 18
is a cross-sectional view showing a structure of a conventional fluorescent bulb lamp device
250
disclosed in PCT Application No. JP00/02054. As shown in the drawing, the fluorescent lamp device
250
comprises: a fluorescent lamp
201
composed of three luminescent tubes each having a generally U-shaped configuration which are coupled to each other with bridges; a lighting circuit
202
including such an element as a semiconductor chip for lighting the fluorescent lamp
201
; a cover
203
for containing the lighting circuit
202
; a mouth ring
204
attached to a tip of the cover
203
; and a globe
205
enveloping the fluorescent lamp
201
.
FIG. 19
is an electric circuit diagram showing a structure of the lighting circuit
202
in the fluorescent lamp device
250
. As shown in the drawing, the lighting circuit
202
is composed of a line filter circuit
212
, a rectifying circuit
213
, a power-supply smoothing capacitor
214
, an inverter circuit
215
, a choke coil
207
, and a resonating capacitor
216
which are disposed in the lighting circuit
202
. The inverter circuit
215
is composed of an inverter driving IC
217
, FETs
208
and
209
which are switching elements driven by the inverter driving IC
217
, and a capacitor
218
for inverter. The fluorescent lamp
201
is disposed in parallel with the resonating capacitor
216
such that fluorescent light is emitted therefrom by allowing a discharge current to flow between electrodes
221
and
222
at both ends in the fluorescent lamp
201
.
In the conventional fluorescent lamp device
250
, the individual circuits are formed as discrete external components and then the line filter circuit
212
, the power-supply smoothing capacitor
214
, the choke coil
207
, the resonating capacitor
216
, the capacitor
218
for inverter, and the like are disposed on a top surface
206
a
of a circuit board
206
, while the rectifying circuit
213
, the inverter driving IC
217
, the FETs
208
and
209
, and the like are disposed on a back surface
206
b
of the circuit board
206
. In short, components having relatively low heat resistance such as the rectifying circuit
213
, the inverter driving IC
217
, and the FETs
208
and
209
in the inverter circuit
215
are disposed on the surface different from the surface on which the choke coil
207
as a heat generating component and the like are disposed in spaced apart relation therefrom.
Since the current flowing in the electrodes
221
and
222
of the fluorescent lamp
202
is large to impart sufficient brightness to the lamp, a pMOSFET and an nMOSFET as power transistors are used as the FETs
208
and
209
disposed in the inverter circuit
215
. On the other hand, a power diode is used as the diode disposed in the rectifying circuit
213
. The basic function of the power device including the power transistor and the power diode is equivalent to that of an AC-DC-AC converter for converting 50/60 Hz to, e.g., 50 kHz. As such a power transistor or a power diode, a power device provided on a SiC substrate as described above is adopted oftentimes.
Problems to be Solved
However, the foregoing conventional fluorescent lamp device has the following problems.
In the conventional fluorescent lamp device
250
, solder or the like is used normally to mount the transistor, diode, and the like on the substrate. However, the transistor, the diode, and the like cannot be positioned adjacent, e.g., a fluorescent lamp which generates a large amount of heat since the solder lacks durability at high temperatures. As a result, the whole fluorescent lamp system is increased disadvantageously in size.
In the lighting circuit
202
formed by mounting the individual components on the circuit board
206
and providing connections therebetween with wires, stringent positional restrictions are placed on the components with low heat resistance to circumvent a temperature increase. As a result, the whole lighting circuit
201
is inevitably increased disadvantageously in size in spite of various considerations given to the positional relations among the individual components.
By using the high heat resistance of a SiC substrate, a semiconductor device provided on the SiC substrate may be placed in equipment used in a high-temperature environment such as the lighting circuit. However, since the power transistor and power diode provided on the conventional SiC substrate are discrete devices, it is difficult to prevent the lighting circuit
202
from being increased in size.
It is therefore an object of the present invention to provide a semiconductor device to be placed suitably under stringent conditions including limited operating temperatures and limited space by providing at least either of active elements and passive elements on a compound semiconductor substrate with high heat resistance.
Disclosure of the Invention
A first semiconductor device according to the present invention comprises: a compound semiconductor layer provided in a substrate; an active region provided on the compound semiconductor layer and composed of at least one first semiconductor layer functioning as a carrier flow region and at least one second semiconductor layer containing an impurity for carriers at a high concentration and smaller in film thickness than the first semiconductor layer such that the carriers are distributed therein under a quantum effect, the first and second semiconductor layers being alternately stacked; and a plurality of active elements provided on the active region.
In the arrangement, if a voltage which brings the active elements into the ON state is applied, the carriers in the second semiconductor layer spread out extensively to the first semiconductor layer so that the carriers are distributed in the entire active region. Because of a low impurity concentration in the first semiconductor layer, scattering of the carriers by impurity ions is reduced in the first semiconductor layer. If a MISFET and a diode are provided on the active region, therefore, carriers flow at a particularly high speed. Moreover, the whole active region is depleted in the OFF state irrespective of an average impurity concentration which is not low in the active region so that the carriers no more exist in the active region. Consequently, the breakdown voltage is defined by the first semiconductor laye

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