3.7.3 Latch-up

Latch up stems from the parasitic bipolar transistors which are structurally inherent to bulk CMOS. These transistors can be activated in various ways and as CMOS technologies are scaled down, this variety grows. Under certain conditions the activated transistors can dominate the circuit behavior. However, with proper process and lay out design, CMOS chips can be operated without ever encountering latch up.

Physical origin

To have both n-channel and p-channel transistors, it is necessary to have both p and n type background material. Figure shows the cross sectional view of an inverter circuit in N-well CMOS process with parasitic bipolar transistors.