Some characteristics of the zero-temperature-coefficient capacitance of an MOS capacitor in accumulation

Abstract

Theoretical consideration shows that the silicon component of the MOS capacitor exhibits a zero temperature coefficient of capacitance for a silicon surface biased in accumulation. A unique surface potential, which can be expressed in terms of material properties, exists at which the surface capacitance becomes independent of temperature. Capacitance-voltage plots for temperatures within 50°C of room temperature provide experimental evidence in support of the theory. A gate bias Vx corresponding to this unique surface potential has been observed. However, a slight broadening of Vx into a small spot extending some 20 mV generally results, and has been shown to be due to the presence of the gate oxide capacitance. Vx is relatively constant over the range of signal frequencies, 10-100 kHz, but varies substantially at higher frequencies. Vx also shows a linear dependence on the gate oxide thickness decreasing at the rate of approximately 1 V/2000 A.