Power Semiconductor Devices

Abstract

This invention generally relates to power semiconductor devices, and in particular to improved thyristor devices and circuits. The techniques we describe are particularly useful for so-called MOS-gated thyristors. We describe a thyristor comprising a plurality of power thyristor devices connected in parallel, each said thyristor device being operable at a device current which the device has an on-resistance with a positive temperature coefficient.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which:

FIG. 1 shows a schematic cross-sectional view of an embodiment of semiconductor devices according to the invention;

FIG. 2 shows I-V characteristics of a thyristor device according to an embodiment of the invention;

FIG. 3 shows an enlargement of FIG. 2;

FIG. 4 shows I-V curves of thyristor devices with the same cathode width and carrier lifetime but different gate width;

FIG. 5 shows the relationship between the gate width and the current density at the crosspoint;

FIG. 6 shows I-V curves of thyristor devices with substantially the same structures but different carrier lifetime;

FIG. 7 shows the relationship between the carrier lifetime and the current density at the crosspoint;

FIG. 8 shows successful turn-on transients of two paralleled wide-gate thyristor devices according to an embodiment of the invention (Va: 20V/div, Vgg: 5V/div, Ia1, Ia2: 10 A/div, t: 2 μs/div);

FIG. 9 shows successful turn-off transients of the two paralleled devices of FIG. 5 (Va: 250V/div, Ia1, Ia2: 50 A/div, T: 2 μs/div);

FIG. 10 shows turn-on failure of two conventional thyristor devices connected in parallel (Va: 40V/div, Vg: 10/div, Ia1, Ia2: 2 A/div, t: 2 μs/div);

FIG. 11 shows an example of a drive circuit for a MOS-gated thyristor according to an embodiment of the invention;

FIG. 12 shows a circuit model of an embodiment of a MOS-gated thyristor according to an embodiment of the invention.

Claims

1. A thyristor comprising a plurality of power thyristor devices connected in parallel, each said thyristor device being operable at a device current at which the device has an on-resistance with a positive temperature coefficient.

2. A thyristor as claimed in claim 1 wherein said device current is less than 10 kA, more preferably less than 1 kA, most preferably less than 100 A.

3. A thyristor as claimed in claim 1 wherein each said thyristor has a MOS gate.

4. A thyristor as claimed in claim 1 comprising a plurality of dies within a single package, each die bearing a said thyristor device.

5. A thyristor as claimed in claim 1 wherein said parallel connecting comprises connecting respective anode, cathode, and gate connections of each thyristor device in parallel.

6. A thyristor as claimed in claim 1 wherein each said device has a gate width of greater than 150 μm.

7. A thyristor as claimed in claim 1 wherein each said thyristor device has a turn-on time of less than 10 μs.

8. A MOS-gated thyristor device modelable as a thyristor connected in parallel with a resistor, and wherein said resistor includes a channel of a MOS transistor driven by said MOS gate.

9. A MOS-gated thyristor as claimed in claim 8 wherein said resistor includes a resistance of a drift region of said thyristor.

10. A MOS-gated thyristor as claimed in claim 8 wherein said thyristor is a power device, and wherein each of said thyristor and said channel is configured to carry a current of at least 10 Amps.

11. A combination of a MOS-gated thyristor and drive circuit, said drive circuit having a gate input, and said drive circuit is configured to step up a voltage on said gate input to provide a gate drive to said MOS gate of said thyristor.

12. A thyristor and drive circuit as claimed in claim 11 wherein said drive circuit includes a charge storage capacitor coupled to said gate input and an energy storage inductor to provide a voltage for charging said capacitor.

13. A thyristor and drive circuit as claimed in claim 12 wherein said inductor comprises a stray inductance associated with said thyristor packaging.

14. A thyristor and drive circuit as claimed in claim 12 further comprising a bypass diode connected between said gate input and said capacitor.

15. A thyristor and drive circuit as claimed in any one of claim 11 wherein said thyristor and said drive circuit are fabricated on a common substrate.

16. A method of fabricating a power thyristor, the method comprising connecting a plurality of thyristor devices in parallel, each said thyristor having a maximum current rating and having an on-resistance with a positive temperature coefficient at said maximum current rating.

17. A method of operating a power thyristor comprising a plurality of thyristor devices connected in parallel, the method comprising passing a current through said power thyristor, when said power thyristor and said thyristor devices are in an on state, such that each of said thyristor devices has an on-resistance with a positive temperature coefficient.