AC analysis of MOSFETs: Device performance, interconnections, and circuit reliability.

摘要

The ac characteristics of MOSFET in terms of device performance, interconnections, and circuit reliability are studied. At device level, the scattering parameters of silicon MOSFETs are measured in the frequency domain for scaled devices. The gate resistance delay effects are characterized and modeled. Simulations using SPICE and measurement data are compared. Qualitatively, L-, II-, T-ladder models are investigated for both the real and imaginary parts of ;For interconnections, polysilicon line capacitances are measured and compared with the simulation results of PISCES. A well isolation technique was used to reduce the parasitic capacitances of the bonding pad. Using this method, the capacitances for different lengths and widths are measured successfully and proved to agree well with simulation results. It is confirmed that small sized test structures are adequate for various measurement purposes using this well isolation technique since the variations of parasitic capacitance various structures can be minimized. From line capacitance measurement data, the fringing capacitance, which becomes important in the horizontally scaled VLSI circuits, is estimated by extrapolation.;For circuits, the metastability of CMOS latch/flip-flops are measured and modeled. An ac frequency domain approach is adopted and this method suggests several optimal design approaches for the inverter ratio, aspect ratio, and circuit configurations. This frequency domain approach proved to be advantageous compared with the usual time domain one. The mean time between failures (MTBF) due to the metastable state has been measured using the late detection method, and the data confirms our optimal design approach. The dependence of the metastability on the Miller effect is studied for the optimal configurations. The power supply disturbance and chip temperature variation effects are measured and compared; they agree well with the ac small signal simulations, therefore confirming the ac small signal frequency domain approach. Parameters such as the threshold voltage, gate oxide thickness, substrate doping, and static noise margin are characterized in terms of their sensitivities on the metastability. Desirable selections of those parameters are suggested as well.