| 摘要 |
<p>1320290 Semi-conductor devices NATIONAL CASH REGISTER CO 22 May 1972 [8 June 1971] 23873/72 Heading H1K The gate insulation of an IGFET 24 is protected by the provision of a further IGFET 16 having an elongate drain region 18 connected at one end 22 to the gate electrode 30 of the protected IGFET 24 and at the other end 19 to an input terminal 21 and to the gate electrode 10 of the protective IGFET 16, which gate electrode 10 overlies a thicker gate insulating layer than that of the protected device. The source region 14 of the protective IGFET is grounded. In the presence of a potentially damaging voltage overload the IGFET 16 switches on, and the gate of the device 24 is protected by the combination of the draining of current to ground through the device 16 and the distributed resistance of the elongate drain region 18. In the event of a higher voltage overload the input end 19 of the drain region 18 can be arranged to operate as an avalanche breakdown diode, shorting the overload directly to the grounded substrate 17. Drain-to-source punch-through of the protective IGFET 16 may also be arranged to occur at a certain voltage level less than that which would damage the IGFET 24.</p> |
