Latchup and its remedies:

What is Latchup?
Latch-up is a condition in which the parasitic components give rise to the Establishment of low
 resistance conducting path between VDD and VSS with Disastrous results. 


(in the figure, moat = substrate)




The start of trouble!





Electron flow builds up voltage





The forward biased source injects some holes





The holes are swept into the substrate





Voltage drop