Analysis of kink phenomenon in S11-parameter of standard RF MOSFETs

For the first time, the low-frequency kink phenomenon in the S₁₁-parameter of standard MOSFETs fabricated without any degradation of RF performances that exists in previous works is reported and its dependence on the gate finger number is analysed. The kink phenomenon is notable only for wide total gate width devices that show abrupt increase of a negative phase angle of the S₁₁-parameter in the low-frequency region, because of a widening space between adjacent resistance circles in the Smith chart. This phase increase originated from a quadratic increase of the low-frequency input capacitance against the gate finger number due to a constant load impedance for the S₁₁-parameter measurement.