Automatic Accurate Display of Capacitance-and Conductance-versus-Bias Characteristics at High Frequencies for Semiconductor Evaluation

An instrument is presented that permits the automatic and rapid measurement of the continuous capacitance-and conductance-versus-bias characteristics of semiconductor devices such as MOS capacitors, varactors and similar structures at 25, 50, or 100 MHz over a wide range of biases (-110to + 110V) and sweep speeds. It has a range of 10 pF and 4 mmho to 100 pF and 40 mmho full scale in 4 steps, an accuracy better than 2 percent and provides outputs for the capacitance C, the conductance G, and the bias Vb of the device under test for graphic display on an X-YY recorder. It is based on an accurate HF current-to-voltage converter in combination with two synchronous detectors. For accuracy reasons the high measuring frequency is converted to a suitable value (5 kHz) by means of a superheterodyne phase-lock loop system and two mixers. Provisions have been made to correct the errors due to parasitic effects. Representative experimental results obtained with the C, G(Vb) instrument are shown.