We investigated the impact of velocity overshoot effect on collector signal delay of bipolar devices by using Monte Carlo simulation method. We found that insertion of an i-layer (lightly doped, intrinsic layer) between base and collector can increase the delay, but the strength of this effect is a function of the i-layer thickness. When the i-layer becomes thinner, the problem of increasing delay seems to disappear. This recovery of delay is realised with a mechanism which is completely different from that in drift-diffusion model.

Junction leakage current of trench isolation devices is strongly influenced by trench configuration. The origin of the leakage current is the mechanical stress that is generated by the differential thermal expansion between the Si substrate and the SiO2 filled isolation trench during the isolation forming process. A two-dimensional mechanical stress simulation was used to analyze trench-isolated devices. The simulated distribution and magnitude of stress were found to agree with Raman spectroscopic measurements of actual devices. The stress in the deeper regions between deep trenches is likely to increase greatly as the size of devices diminishes, so it is important to reduce this stress and thus suppress junction leakage current.