| 摘要 |
The described embodiments of the present invention provide an input protection device with a low trigger threshold. The structure is a silicon controlled rectifier (SCR) type of device wherein the triggering mechanism is avalanche conduction at the interface between the N-well surrounding a portion of the protection device and the P-type substrate. The embodiments provide a lowered threshold voltage by providing a highly doped region of the same conductivity type as the well at the interface between the well and the substrate. This highly doped region is connected to a resistor which is then connected to the protected node. The resistor and heavily doped region at the intersection between the N-well and substrate provides an additional source of current for avalanching at a lower voltage. Thus the trigger voltage of the protection system is substantially lowered. In other embodiments of the present invention an additional source of triggering current is provided by an N+ contact region in the N-well which is close to the interface between the N-well and the P substrate adjacent to the area closest to the N+ emitter of the silicon controlled device. Either of these highly doped charge injection regions may be fed by resistors fabricated with the heavily doped regions themselves or may utilize the N-well itself as a resistive element.
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