Optical imaging of picosecond switching in CMOS circuits

Hot electron light emission is used to measure the propagation of signals through the individual gates in fully functional CMOS circuits. The experiment used an imaging microchannel plate photomultiplier as a detector. Time resolution is obtained by photon timing over a repetitive electrical waveform. CMOS ring oscillators and counters are used as model circuits, fabricated with an effective gate length of 0.6 μm. A series of time-resolved images have been overlaid and assembled into a video. By measuring the voltage dependence of the emission intensity, and from comparisons between circuits with different effective gate lengths, it is shown that the emission process depends on the electric field inside the device.