What is the Latch-up effect in VLSI?
“Latch-up is the state where a semiconductor undergoes a high-current state or low impedance path as a result of the interaction of PNP and NPN bipolar transistors. Latch-up is a phenomenon whereby Vdd and Vss in a CMOS device become structurally shorted due to the effect of noise or etc.”
Reason for the Latch-up
- Low Impedance path between Substrate and well.
- Minority carriers inject into the substrate or well
- Short circuit between Vdd and Vss
- Temperature effects can also influence the Latch-Up immunity of products. because as temperature increases, the substrate and well resistances rise to allow the bias to reach a critical value sooner.
- The effective distance between the N+, P+, and N-Well diffusion narrows allowing easier capture of excited carriers.
How to reduce the latch-up effect || How to avoid the Latch-up effect.
- Use More Tap(Bulk) for Digital Circuit Layout
- Use a Guard ring for the Analog layout.
- Keep more distance between Pmos & Nmos
- Give more Enclosure of Newell
- Use the halo doping concept
- Use an EPI(epitaxial layer) layer.
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