Sensitive permittivity detector for dielectric samples at 120 GHz

This work describes a dielectric sensing system applying a 120 GHz electrical interferometer for contactless permittivity measurements. The applied IC was fabricated in a 130 nm SiGe process featuring an ft and fmax of 240 GHz and 330 GHz. The on-chip system contains a 120 GHz VCO with a tuning range of 7 GHz featuring a divide-by-64 circuit to enable external PLL operation. An important feature of the IC is high-precision and high-resolution phase shifting based on a slow-wave transmission lines approach with digital control. This allows for direct digital readout ability. The on chip power detector provides DC output signals giving the opportunity to record transfer functions of the interferometer. It enables sample emulation capability by phase shift inducement in the measurement as well as a reference transmission line. The motherboard of the system provides PLL stabilization for frequency sweeps. The proposed approach is capable of automated dielectric monitoring by phase compensation.