last updated June 3, 1999

When the polysilicon beam contacts the underlying nitride layer, the system behaves like a variable capacitor that is very sensitive to contact conditions. By measuring the changes in capacitance as a function of applied voltage and time, effective surface compressibility and dielectric charging can be measured. Measured and simulated CV curves Dielectric Charging The capacitance of the system continues to increase with time as the voltage is held steady. This is due to charge buildup in the nitride which increases the attractive force on the polysilicon beam. The rate of charging corresponds to charge injection through direct tunneling. Surface Effects The measured CV curves could not be matched by simulations assuming ideal contact conditions. A compressible surface model allows the effective gap between the polysilicon beam and substrate to decrease with applied voltage (and hence applied surface pressure). This compression effect could be due to asperities or surface residue distributed over the contact surfaces. This general behavior is verified by the CV measurement of a flat plate where no zipping occurs yet the capacitance still increases with voltage. CV curve of flat plate (no zipping)