High current MOS device with avalanche protection and method of operation

Abstract

Particularly in high current applications, impact ionization induced electron-hole pairs are generated in the drain (74) of an MOS transistor (51) that can cause a parasitic bipolar transistor (38) to become destructively conductive. The holes pass through the body region (76) of the MOS transistor (51), which has intrinsic resistance, to the source (80), which is typically held at a relatively low voltage, such as ground. The hole current causes a voltage to develop in the body region (76), which acts as the base (42). This increased base voltage is what can cause the parasitic bipolar transistor (38) to become conductive. The likelihood of this is greatly reduced by developing a voltage between the source (80), which acts as the emitter (44), and the body region (76) by passing the channel current through an impedance (62) between the source (80) and the body region (76). This causes the emitter voltage to increase as the base voltage is increased and thereby prevent the parasitic bipolar transistor (38) from becoming conductive.

Description

technical field [0001] The present invention relates generally to semiconductors and, more particularly, to high current MOS devices with avalanche protection and methods of operation. Background technique [0002] As power device dimensions continue to shrink, energy performance is of great concern. In fact, the size of the power MOS device is no longer limited by the working resistance, but instead is limited by the energy performance. As far as automation applications are concerned, the energy demands placed on power MOS devices can lead to significant increases in device temperature, sometimes leading to electrical failure of the corresponding devices due to snapback. Furthermore, parasitic bipolar transistors inherent in power MOS devices lead to electro-thermal failure of individual devices, preventing them from reaching the purely thermal limit of the device. [0003] FIG. 1 is a cross-sectional view of an LDMOSFET device 10 according to the prior art. LDMOSFET dev...

AI Technical Summary

Problems solved by technology

Under high current conduction and high drain-source voltage operating conditions, parasitic bipolar transistor 38 can cause electro-thermal failure of device 10, preventing device 10 from reaching its purely thermal limit

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