An Insertion Thermoelectric RF MEMS Power Sensor for GaAs MMIC-Compatible Applications

Abstract

Design, fabrication and measurement of an X-band inline insertion thermoelectric radio frequency (RF) microelectro- mechanical systems power sensor are proposed in this letter. It is based on sensing a portion of the RF power dissipated by a gradient coplanar waveguide (CPW) due to the intrinsic ohmic losses and converted into thermovoltages by thermopiles, where the thermopiles are inserted below suspended ground planes of the CPW. In the thermopiles' design, cold junctions are covered with the CPW ground planes to reduce the reflection loss by depressing the electromagnetic coupling and serve as hot sink, while hot junctions are covered with the CPW signal plane to increase the sensitivity by improving the temperature of the end. This power sensor is fabricated by the GaAs MESFET process. Measured reflection losses are less than ${-}16.1$ dB and insertion losses are better than 0.4 dB at 8–12 GHz. Experiments show that this improved insertion power sensor has good linearity of the output response, and results in average sensitivities of about 49.3, 35.1, and 47.9 $\mu$ V $\cdot$ mW $^{-1}$ at 8, 10, and 12 GHz, respectively.