Abstract
Wideband and low-loss microwave power measurements are becoming increasingly important for microwave communication and radar systems. To achieve such a power measurement, this paper presents the design and measurement of wideband DC-25 GHz and low-loss MEMS thermoelectric power sensors with a floating thermal slug and a reliable back cavity. In the sensors, the microwave power is converted to thermovoltages via heat. The collaborative design of the thermal slug and the back cavity, i.e., two thermal flow paths, is utilized to improve the efficiency of heat transfer and to ensure reliable applications. These sensors are required to operate up to 25 GHz. In order to achieve low microwave losses at the bandwidth, the floating thermal slug is designed instead of the grounded one. The effects of the floating slug on the reflection losses are analyzed by the simulation. The fabrication of these sensors is completed by GaAs monolithic microwave integrated circuits (MMIC) and micro-electro-mechanical systems (MEMS) technology. Measured reflection losses are less than −25.6 dB up to 12 GHz and −18.6 dB up to 25 GHz. The design of the floating thermal slug reduces the losses, which is equivalent to improving the sensitivity. At 10 and 25 GHz, experiments exhibit that the sensors result in sensitivities of about 51.13 and 35.28 μV/mW for the floating slug and 81.68 and 55.20 μV/mW for the floating slug and the cavity.
Highlights
With the rapid development of multi-band microwave communication and radar systems, the wideband and low-loss power measurements become more and more important for microwave signals
For the overlapping lengths of 2, 10, and 14.5 μm, the simulated reflection losses are less than −24.8, −21.1, and −19.8 dB at DC-25 GHz, respectively. These results show that the proposed power sensors exhibit the low reflection losses, which verifies the design validity of the floating thermal slug
GaAs is thinned to 100 μm in thickness, and the substrate membrane underneath the resistors and the hot end is implemented by a via-hole etching technique
Summary
With the rapid development of multi-band microwave communication and radar systems, the wideband and low-loss power measurements become more and more important for microwave signals. The commonly used power measurement methods include three types: diode-, thermistor-, and thermopile-based microwave power sensors [1,2]. In order to choose the proper configuration and size of the membrane, the thermopile-based MEMS power sensors with dual thermal flow paths are proposed, where the grounded thermal slug and the cavity are included [17]. The grounded slug makes part of the two load resistors short circuit, resulting into smaller resistance and higher reflection losses at high frequencies. They only operate below 12 GHz due to the limitation of reflection losses
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