Internal node probing of a DRAM with a low-temperature e-beam tester

In order to measure signals on internal nodes of circuits operated at liquid-nitrogen temperature, all electron-beam (e-beam) tester has been modified to cool circuits to this temperature during test. This apparatus has made it possible to measure signals on internal nodes of a high-speed DRAM operated at low temperature. The waveforms, which cannot be measured by other methods, provide the only means of determining the internal operation of the circuit. The instrument is described, and measurements of some critical DRAM signals are presented. In particular, the constancy of the bit-line equalization level, is shown, and observations of the interrelationship between power supply voltage, power bus noise, access time, and temperature are reported