Time-resolved optical characterization of electrical activity in integrated circuits

If the rate of improvement in the performance of advanced silicon integrate d circuits is to be sustained, new techniques for the measurement of electr ical waveforms in operating circuits are needed. Critical factors dictating this requirement include the increased speed and complexity of circuits, t he growing importance of faults that appear only during high-speed operatio n, and the use of flip-chip packaging technologies, Two recently del eloped all-optical methods for measuring the switching activity from the backside of a chip are described and compared One is a passive approach based on th e measurement of hot carrier luminescence emitted from the channel of a CMO S field-effect transistor (FET) during switching. The second uses a laser p robe to sense the switching induced modulation of the silicon optical const ants near an FET's source and drain.