A lateral silicon-controlled rectifier (SCR), a modified vertical SCR and a modified lateral SCR with the same device width are fabricated in a 0.25-μm Bipolar-CMOS-DMOS high-voltage process. Key factors affecting the trigger voltage of SCRs are investigated by simulation and transmission line pulse tests. The simulation results show that the trigger voltage depends on the doping concentration, the space charge width and the vertical depth of the breakdown junction. The experimental results indicate that the trigger voltage can be decreased from 40 V to 15 V when the space charge width and the vertical depth of breakdown junction decrease appropriately
