Bipolar junction transistors device structures

CMOS devices can develop a serious problem called latchup, in which junctions in different devices connect and form a forward-biased diode structure, leading to a catastrophic current which destroys the circuit. As illustrated in Fig. 14.5a, the latchnp is caused by the formation of a pnpn device between the terminal of VSS and VDD (see Chap. 9, Sect. 1.3). In a latchup condition, the pnpn device is biased snch that the collector current of the pnp bipolar transistor supplies a base current to the npn bipolar transistor in a positive feedback situation. The latchup can cause device function failure or even self-bumout. Figure 14.5b shows the bipolar components and resistive components of a latchup configuration. The conduction state of a pnp device requires Vq, and the conduction state... 

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