A 125-GHz Permittivity Sensor With Read-Out Circuit in a 250-nm SiGe BiCMOS Technology

In this paper, an integrated dielectric sensor with a read-out circuit in an unmodified SiGe BiCMOS technology at 125 GHz is presented. The sensor consists of a 500-μm shorted half-wave coplanar-waveguide transmission line in the uppermost metal layer of the silicon process, while the read-out is obtained by reflection coefficient measurement with an integrated reflectometer and a signal source. The reflectometer is verified with a circuit breakout including an integrated dummy sensor. The reflectometer is able to measure the phase of the reflection coefficient from 117 to 134 GHz with a resolution of 0.1° and a standard deviation of 0.082°. The integrated sensor with the reflectometer circuit have been fabricated in a 190-GHz fT SiGe:C BiCMOS technology. It spans an area of 1.4 mm² and consumes 75 mA from a 3.3-V supply. The circuit has been assembled on a printed circuit board for characterization by immersion into test liquids. The sensor is controlled by a controller board and a personal computer enabling a measurement time of up to 1 ms per frequency point. Functionality of the sensor is demonstrated from 118 to 133 GHz with immersion of the sensor into different binary methanol-ethanol mixtures, showing good correlation between theory and measurement. The sensor shows a standard deviation of the measured phase of 0.220° and is able to detect a difference in ε´r of 0.0125.