Flexible picosecond probing of integrated circuits with chopped electron beams

The effective design and evaluation of high-speed integrated circuits is supported by internal noninvasive voltage-measurement techniques with picosecond time resolution. An electron-beam tester has therefore been developed which approaches the theoretical time-resolution limit of this method. It is based on the well-established e-beam technique for VLSI circuits, allowing for high flexibility in driving different kinds of high-frequency circuits under both conventional and critical conditions. The electron pulses of the stroboscopic test system are generated by a two-stage chopping system which was optimized to obtain very short pulses. It allows for a 7-ps effective pulse width which simultaneously yields a probe diameter of 0.5 µm and a probe current of 1 nA. This current results in a noise voltage of 20 mV when one period of a 1-GHz signal is recorded, with a total acquisition time of 0.1 s. Long-range phase shifting with high resolution is achieved by operating the upper stage of the blanking system at a high frequency and using the lower one as a selective gate. This allows propagation-delay measurements to be performed with a resolution of better than 2 ps over a range of several µs. The test system has thus far been used for that analysis of tunnel diodes, step-recovery diodes, bipolar frequency dividers, ring oscillators, and GaAs memories. Waveform measurement and evaluation at more than 60 different test points of a GaAs 1-kb SRAM in a six-hour session has demonstrated routine handling of complex high-speed circuit analysis.