Semiconductor device and snubber device having a SiC-MOSFET and a Zener diode

A semiconductor device of the present invention includes a switching transistor, and a recovery diode and a snubber device which are mounted on a single conductive substrate (frame) on which the switching transistor is also mounted. The snubber device includes a SiC-MOSFET connected between an output terminal C and a reference terminal E of the switching transistor, a Zener diode formed between a gate terminal G and a drain terminal D of the SiC-MOSFET, and a resistor formed between the gate terminal G and a source terminal S of the SiC-MOSFET. The reference terminal E of the switching transistor, the source terminal S of the SiC-MOSFET, and an anode terminal of the recovery diode are commonly connected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a snubber device which suppresses a surge voltage generated at a time of turn-off of a switching element or a reverse recovery of a diode used in an inverter or a chopper circuit, and also to a semiconductor device using the snubber device.

2. Description of the Background Art

In an inverter semiconductor module using a switching element having a high switching rate, such as an IGBT, a high voltage (turn-off surge voltage) is generated in floating inductance of a main circuit due to a rapid change of a current at a time of turn-off. At a time when a free-wheeling diode is turned off, a surge voltage (recovery surge voltage) is generated on the same principle.

Thereby, an external protection circuit (snubber device) which absorbs such a surge voltage is provided to a semiconductor module, to thereby suppress the surge voltage. In a typical basic configuration of the snubber device, a resistance R, a diode D, and a capacitor C are combined (for example, Japanese Patent Application Laid-Open No. 2010-115099), a resistance value and the capacitance of a capacitor are adjusted by wiring inductance of an application and the level of a drive current.

Although the external snubber device is an element necessary for a safe operation of a switching element, it is necessary to design heat dissipation of the snubber device itself, which increases the size as an application. Additionally, there is a problem of increased costs and efforts due to low-inductance wiring designing.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor device including a snubber device which suppress costs of heat dissipation designing and wiring designing.

A semiconductor device of the present invention includes a switching transistor, a recovery diode, and a snubber device. The recovery diode and the snubber device are mounted on a single conductive substrate on which the switching transistor is also mounted. The snubber device includes a SiC-MOSFET, a Zener diode, and a resistor. The SiC-MOSFET is connected between an output terminal and a reference terminal of the switching transistor. The Zener diode is connected between a gate terminal and a drain terminal of the SiC-MOSFET. The resistor is connected between the gate terminal and a source terminal of the SiC-MOSFET. The reference terminal of the switching transistor, the source terminal of the SiC-MOSFET, and an anode terminal of the recovery diode are commonly connected.

The semiconductor device of the present invention includes the recovery diode and the snubber device which are mounted on the single conductive substrate on which the switching transistor is also mounted. This allows unification of a cooling system for the snubber device with a cooling system for the switching transistor, to downsize a package. Additionally, it is attractive to some end users, because the snubber is not needed.

A snubber device of the present invention is a snubber device which absorbs a surge voltage of a switching transistor. The snubber device of the present invention includes a SiC-MOSFET, a Zener diode, and a resistor. The Zener diode is connected between a gate terminal and a drain terminal of the SiC-MOSFET. The resistor is connected between the gate terminal and a source terminal of the SiC-MOSFET.

When the snubber device of the present invention is connected in parallel with a circuit including a plurality of switching transistors, the number of snubber devices can be reduced as compared with a case where the snubber device is individually provided for each of the switching transistors. Thus, low costs are realized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a circuit diagram of a switching module which is an example of a semiconductor device according to this preferred embodiment. The switching module includes an IGBT1which is a main switching element, a recovery diode2connected between a collector C and an emitter E of the IGBT1, and a snubber device6which absorbs a surge voltage. The snubber device6includes a SiC-MOSFET3connected between the collector C and the emitter E of the IGBT1, a Zener diode4connected between a drain D and a gate G of the SiC-MOSFET3, and a resistor5connected between the gate G and a source S of the SiC-MOSFET3. As the SiC-MOSFET3, for example, N-channel enhancement-mode one is used. Each of the Zener diode4and the resistor5is formed of polysilicon.

A threshold voltage of the Zener diode4is normally set higher than a power supply voltage which is applied to the collector of the IGBT1. When the surge voltage exceeds the threshold voltage of the Zener diode4, a voltage drop occurs in the resistor5, so that a gate voltage of the SiC-MOSFET3is raised to bring the SiC-MOSFET3into an ON state. Since large part of surge energy passes through the SiC-MOSFET3and is consumed (active clamp), the risk of application of an excessive surge voltage to the IGBT1and the recovery diode2is reduced (seeFIG. 2).

FIG. 3is diagram showing a configuration of the switching module. The IGBT1, the recovery diode2, and the snubber device6are mounted on a single lead frame, and a collector terminal C, an emitter terminal E, a gate terminal G, and a sense terminal SE of the IGBT1are exposed to the outside of a package.

FIG. 4is a plan view of a chip of the snubber device6as seen from the upper side. A drain electrode D of the SiC-MOSFET3is formed on a back surface of the chip. A source electrode S of the SiC-MOSFET3is formed on a surface of the chip. A gate electrode G of the SiC-MOSFET3is formed around the source electrode S. Additionally, a guard ring layer9is formed around the gate electrode G. The Zener diode4is formed on the guard ring layer9, and the resistor5is formed between the gate electrode G and the source electrode S of the SiC-MOSFET3.

In the switching module of this preferred embodiment, the IGBT1which is a switching element and the snubber device6which absorbs the surge voltage are mounted on a single lead frame in this manner. This contributes to improvement of the system security and in addition to downsizing.

Conventionally, such a snubber device is provided as an external device to a package of a switching element. However, configuring a snubber device by using a power MOSFET allows the snubber device to be mounted on the single lead frame on which the switching element is also mounted. Moreover, by using SiC which is a wide-bandgap material for the power MOSFET, heat generation due to a snubber loss can be suppressed, to allow unification of a cooling system for the snubber device6with a cooling system for the switching element. Consequently, the system as a whole can be downsized.

If the snubber device6is disposed immediately near a switching element needing a protection within the single lead frame, parasitic inductance can be minimized to obtain the maximum protection performance.

The semiconductor device according to the preferred embodiment 1 provides the following effects. The semiconductor device of this preferred embodiment includes the switching transistor1, the recovery diode2and the snubber device6which are mounted on a single lead frame on which the switching transistor1is mounted. The snubber device6includes the SiC-MOSFET3connected between an output terminal (collector terminal C) and a reference terminal (emitter terminal E) of the switching transistor (IGBT1), the Zener diode4formed between the gate terminal G and the drain terminal D of the SiC-MOSFET3, and the resistor5formed between the gate terminal G and the source terminal S of the SiC-MOSFET3. The emitter terminal E of the switching transistor1, the source terminal of the SiC-MOSFET3, and an anode terminal of the recovery diode are commonly connected. This allows unification of a heat dissipation system for the snubber device6with a heat dissipation system for the switching transistor1, thus enabling downsizing of the system as a whole. By disposing the snubber device6immediately near the switching transistor1on the single lead frame, the parasitic inductance can be minimized to obtain the maximum protection performance.

The Zener diode4and the resistor5are formed on the single chip on which the SiC-MOSFET3is also formed. The above-mentioned effects are obtained by this configuration.

In the preferred embodiment 1, the Zener diode4and the resistor5which are necessary for the active clamp are formed on the single chip (snubber device6) on which the SiC-MOSFET3is also formed. While the SiC-MOSFET3which absorbs the surge energy is a SiC device operable at a high temperature, the Zener diode4and the resistor5are formed of polysilicon and therefore their performance is reduced in a high-temperature operation, which causes a bottleneck.

In a preferred embodiment 2, therefore, the SiC-MOSFET3which generates heat in an active clamping operation is formed as an element separate from the Zener diode4and the resistor5which have no energy load, so that the protection performance against larger surge energy can be exhibited.

FIG. 5shows a circuit diagram of a switching module which is an example of a semiconductor device according to the preferred embodiment 2. The same component parts as those of the preferred embodiment 1 are denoted by the same corresponding reference numerals. The circuit diagram shown inFIG. 5is the same as the circuit diagram of the preferred embodiment 1 shown inFIG. 1, except that a chip on which the Zener diode4and the resistor5are provided is different from a chip on which the SiC-MOSFET3is provided.

FIG. 6is a diagram showing a configuration of the switching module. The IGBT1, the recovery diode2, a first snubber device6aincluding the SiC-MOSFET3, a second snubber device6bincluding the Zener diode4and the resistor5are mounted on a single lead frame. The collector terminal C, the emitter terminal E, the gate terminal G, and the sense terminal SE of the IGBT1are exposed to the outside of a package.

FIG. 7is a plan view of a chip of the first snubber device6aas seen from the upper side. The drain electrode D of the SiC-MOSFET3is formed on a back surface of the chip. The source electrode S of the SiC-MOSFET3is formed on a surface of the chip. The gate electrode G of the SiC-MOSFET3is formed around the source electrode S. A gate pad8is formed adjacent to the gate electrode G, and the guard ring layer9is formed around the gate electrode G.

FIG. 8is a plan view of a chip of the second snubber device6bas seen from the upper side. The source terminal S serving as a common terminal which is conducted to the source terminal S of the SiC-MOSFET3is formed on a surface of the chip. A gate pad8is formed on the source terminal S. The resistor5is formed adjacent to the gate pad8. The guard ring9is formed around the source terminal S, and the Zener diode4is formed on the guard ring9. An outer periphery of the guard ring9serves as a channel cut part10.

The semiconductor device according to the preferred embodiment 3 provides the following effects. In the semiconductor device of this preferred embodiment, the Zener diode4and the resistor5made of polysilicon are formed on the chip separate from the chip on which the SiC-MOSFET3is provided. Thereby, the bottleneck in the high-temperature operation is eliminated so that the protection performance can be exhibited against larger surge energy.

In the configuration of the preferred embodiment 2, the special semiconductor device (second snubber device6b) is required for arranging the Zener diode4and the resistor5necessary for the active clamping operation. In a preferred embodiment 3, a silicon device is used as the IGBT1, and the Zener diode4and the resistor5are formed on a single device (switching device7) on which the IGBT1is also formed. Thereby, the number of chips and the number of wirings are decreased and cost reduction is realized.

FIG. 9shows a circuit diagram of a switching module which is an example of a semiconductor device according to the preferred embodiment 3.FIG. 10is a diagram showing a configuration of the switching module. InFIGS. 9 and 10, the same component parts as those of the preferred embodiment 2 are denoted by the same corresponding reference signs.

In the switching module, as shown inFIG. 10, the switching device7, the recovery diode2, and the snubber device6aincluding the SiC-MOSFET3are mounted on a single lead frame. The collector terminal C, the emitter terminal E, the gate terminal G, and the sense terminal SE of the IGBT1are exposed to the outside of a package. The switching device7is a Si device, on which the IGBT1, the Zener diode4, and the resistor5are formed.

The semiconductor device according to the preferred embodiment 3 provides the following effects. In the semiconductor device of this preferred embodiment, the IGBT1is configured as a Si substrate, and the Zener diode4and the resistor5are formed on the single device (switching device) on which the IGBT1is also formed. Thereby, the bottleneck in the high-temperature operation is eliminated, and moreover the number of chips and the number of wirings are reduced to allow cost reduction.

FIG. 11shows a circuit diagram of a switching module which is an example of a semiconductor device according to a preferred embodiment 4, andFIG. 12is a diagram showing a configuration of the switching module. InFIGS. 11 and 12, the same component parts as those of the preferred embodiment 1 are denoted by the same corresponding reference signs. The switching module of this preferred embodiment is different from that of the preferred embodiment 1 in that a body diode11of the SiC-MOSFET3is used as a recovery diode of the IGBT1.

As shown inFIG. 12, in the switching module, the IGBT1and the snubber device6are mounted on a single lead frame, and the collector terminal1, the emitter terminal E, the gate terminal G, and the sense terminal SE of the IGBT1are exposed to the outside of a package.

In the semiconductor device of the preferred embodiment 4, the body diode of the SiC-MOSFET3is used as the recovery diode of the IGBT1, and thereby the recovery diode can be omitted so that the cost reduction can be realized.

FIG. 13shows a circuit diagram of a snubber device of this preferred embodiment, andFIG. 14is a diagram showing a configuration of the snubber device of this preferred embodiment. A circuit configuration of the snubber device is the same as that of the snubber device of the switching module of the preferred embodiment 1, except that only the snubber device6is formed as a single package as shown inFIG. 14. The same component parts as those of the preferred embodiment 1 are denoted by the same corresponding reference numerals. The snubber device6is mounted on a lead frame, and the drain terminal D and the source terminal S of the SiC-MOSFET3are exposed to the outside of the package.

As shown inFIG. 15, this snubber device is used as a lump snubber which is connected in parallel with an inverter module12including a plurality of switching elements. Adoption of this configuration allows reduction in the number of snubber devices as compared with a case where a snubber device is individually provided for each of the switching elements, and thus allows the cost reduction.

In the configuration of the snubber device, the Zener diode4and the resistor5are configured on a device on which the SiC-MOSFET3is also formed. Here, it may also be possible that the Zener diode4and the resistor5are configured as separate devices as in the preferred embodiment 2. In this case, the bottleneck in the high-temperature operation can eliminated, and the protection performance against larger surge energy can be exhibited.

The snubber device according to this preferred embodiment provides the following effects. The snubber device6of the preferred embodiment 5 is a snubber device which absorbs surge voltage of the switching transistor, and includes the SiC-MOSFET3, the Zener diode4formed between the gate terminal G and the drain terminal D of the SiC-MOSFET3, and the resistor5formed between the gate terminal G and the source terminal S of the SiC-MOSFET3. By connecting this snubber device6collectively to the inverter module including the plurality of switching elements, the number of snubber devices can be reduced to realize the cost reduction.

The snubber device6absorbs the surge voltage of the inverter module12including the plurality of switching transistors. By connecting the snubber device6in parallel with the inverter module12, the number of snubber devices can be reduced to realize the cost reduction.