attoF MOS varactor RF measurement VNA coupled with interferometer

Nowadays with capabilities offered by advanced silicon technologies both for design above 60GHz and for high performance Digitally Controlled Oscillator, the use of sub fF varactor is mandatory. One of the challenge to develop this device is to be able to characterize it accurately for process optimization and modeling. In high and above all low frequency range, this type of measurement has to face with the issue of high impedance characterization and mismatch regarding 50Ω. In the RF range, Agilent is developing an interferometer module added to a VNA able to characterize very low capacitance. In this paper, we evaluate this equipment using dedicated calibration silicon structures to measure 500aF MOS varactor and compare measurement to developed electrical model.