A direct measurement technique for small geometry MOS transistor capacitances

Abstract

Accurate representation of MOS transistor capacitances is important for accurate circuit simulation. Due to the difficulties of direct measurement with meters, MOS intrinsic capacitances have not been studied extensively. Although several "on-chip" methods have been developed, the need for measurement circuits fabricated alongside the devices of interest seems to be impractical for statistical data generation. In addition, the characterization of both current-voltage ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</tex> ) and capacitance-voltage (CV) relationships is not as convenient by using the "on-chip" configurations. Consequently, the direct measurement technique is more desirable than the "on-chip" methods. A direct measurement technique for the intrinsic gate capacitances in a small geometry MOS transistor has been developed and is presented in this letter. By using this method, n-channel transistors with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W_{eff}/L_{eff}</tex> of, 11/11, 11/2.2, and 11/1.65 µm have been measured. The difference between the long- and short-channel devices can be clearly observed in the measured curves. The results show that the small MOSFET intrinsic capacitances can be accurately determined using off the self meters, and the use of "on-chip" circuitry is unnecessary.