Design of precision capacitors for analog applications

The authors describe and analyze two capacitors which are incorporated in a baseline BiCMOS technology without added process complexity. The first capacitor is formed between degenerated doped polysilicon and silicon. The second is formed between two degenerately doped polysilicon layers. In both structures, the insulator is a deposited or grown oxide. The sensitivity of the capacitor voltage coefficient to oxide thickness and surface dopant concentration is discussed theoretically and compared to measured data. The two capacitors are optimized to exhibit very low voltage coefficients.<>