A Fully Integrated Low-Power 30 GHz Complex Dielectric Sensor in a 0.25-$\mu$m BiCMOS Technology

Abstract

This paper presents an integrated low-power dielectric sensor in K-band frequencies implemented in a $0.25 \mu \mathrm{m}$ SiGe BiCMOS process, including the sensing front-end and readout circuits. The sensor enables the measurement of both real and imaginary part of permittivity of the material under test (MUT). The MUT is exposed on the resonator component in a sensing oscillator, and the oscillator results in permittivity- and conductivity-dependent change in the output frequency and output power, respectively. The frequency information is translated into dc voltage using a frequency discriminator, and the output power is detected using a power detector. The sensor has been calibrated using iso-propanol, ethanediol, and acetone solutions. Methanol–ethanol mixture solutions, in steps of 25% of concentration change, have been used to demonstrate the functionality of the sensor. The selectivity is showed using methanol–ethanol mixtures with concentration differences of 5% around a mixture ratio of 50:50. The chip is $2.3 \text{mm}^{2}$ in size and consumes 60 mW power. The sensor measures complex permittivity within 3.7% accuracy for the real part and 4.3% for the imaginary part. As a compact and low-power solution, the sensor is a potential candidate for minimal invasive investigations of chemicals and bio-materials at mm-wave frequencies.