Semiconductor switch including a power transistor integrated with a temperature sensor therefor

Claim 1

A semiconductor switch comprising a power transistor and a temperature sensor integrated therewith for providing a control signal to switch off the power transistor when the sensor reaches a predetermined thermal condition; said power transistor being an insulated gate field effect transistor formed by a semiconductor body (10) having therein a first region (13) of a first conductivity type adjacent a surface of said body and a plurality of device cells (11) in said body, each device cell (11) comprising a second region (32) within said first region (13) and which is of a second conductivity type opposite to said first conductivity type; a third region (33) within the second region (32) and which is of said first conductivity type; and an insulated gate (34) overlying a conduction channel (35) formed thereby in said second region (32) for providing a gatable conductive path between the third region (33) and the first region (13); said temperature sensor comprising a thermally responsive semiconductor device formed by a plurality of further device cells (11') within the semiconductor body (10), each said further device cell (11') comprising a further second region (32') within said first region (13) and which is of said second conductivity type; a further third region (33') within the further second region (32') and which is of said first conductivity type; and a further insulated gate (34') overlying a conduction channel (35') formed thereby within the further second region (32'), said further gate (34') being electrically connected to either of said third and further third regions (33, 33'); said further device cells constituting a parasitic bipolar transistor having a leakage current which varies with temperature and from which the temperature sensor derives a control signal for switching off the power transistor when said predetermined thermal condition is reached.