Correlation of frequency hopped VCO phase settling to varactor transient capacitance

Microwave VCO and system designers should be aware that attoFarad level changes in the dynamic performance of a varactor can correlate to changes in system settling response of fast hopping frequency synthesizers. It is theorized that a moisture/silicon interaction occurred within a packaged varactor diode due to imperfect wafer processing of the die and a flawed ceramic enclosure. The flawed ceramic allowed ambient moisture to penetrate and come in contact with exposed silicon at the surface of the die junction, causing an increase in interface (or surface) states which in turn increased the settling time constant of diode capacitance on the order of fifty microseconds. The increased time constant was correlated to an observed degradation in VCO phase settling. The increased phase transient was shown to recover with several time/temperature combinations in accordance with Arrhenius predictions