Characteristics of Doped n+ GaAs Thermopile-Based RF MEMS Power Sensors for MMIC Applications

This letter presents characteristics of thermopile-based radio frequency microelectromechanical system (RF MEMS) power sensors with different doped n± GaAs concentrations, in order to improve sensitivity and signal-noise ratio (SNR). These sensors employ the conversion principle of RF power-heat-electricity, where two materials of AuGeNi/Au and n± GaAs are designed to constitute two arms of the thermopile. The effects of four doping concentrations of n± GaAs on the sensitivity and SNR of the power sensors are investigated. The RF MEMS power sensors are fabricated by a GaAs monolithic microwave integrated circuit (MMIC)-compatible process. Experiments show that these power sensors produce return losses of less than -28.3 dB up to 20 GHz. For the doped n± GaAs concentrations of 2.4 × 10¹⁸, 8.5 × 10¹⁷, 3.2 × 10¹⁷, and 1.9 × 10¹⁷ cm^-3, measured sensitivities are about 84.10, 101.04, 209.82, and 395.52 μV/mW at 1 GHz and about 45.87, 54.11, 104.15, and 212.53 μV/mW at 20 GHz, respectively, while the resulting SNR are about 4.27 × 10⁶, 3.08 × 10⁶, 3.91 × 10⁶, and 5.70 × 10⁶ W^-1 at 1 GHz and about 2.33 × 10⁶, 1.65 × 10⁶, 1.94 × 10⁶, and 3.06 × 10⁶ W^-1 at 20 GHz, respectively. With the decrease of doping concentration, the sensitivity increases but the SNR decreases first and then increases.