Backside optical measurements of picosecond internal gate delays in a flip-chip packaged silicon VLSI circuit

A report is presented of the backside optical measurements of internal gate propagation delays in a flip-chip mounted silicon integrated circuit. Both gate delays and risetimes agreed well with prior simulations. However, the measurements displayed additional features on the signals that were not seen in the simulations, such as feedforward through devices, signal over/undershoot, and circuit switching noise on the power supply.< >