Liao Xiao-ping

Design and fabrication of a terminating type MEMS microwave power sensor

A terminating type MEMS microwave power sensor based on the Seebeck effect and compatible with the GaAs MMIC process is presented. An electrothermal model is introduced to simulate the heat transfer behavior and temperature distribution. The sensor measured the microwave power from −20 to 20 dBm up to 20 GHz. The sensitivity of the sensor is 0.27 mV/mW at 20 GHz, and the input return loss is less than −26 dB over the entire experiment frequency range. In order to improve the sensitivity, four different types of coplanar waveguide (CPW) were designed and the sensitivity was significantly increased by about a factor of 2.

A capacitive membrane MEMS microwave power sensor in the X-band based on GaAs MMIC technology

This paper presents the modeling, fabrication, and measurement of a capacitive membrane MEMS microwave power sensor. The sensor measures microwave power coupled from coplanar waveguide (CPW) transmission lines by a MEMS membrane and then converts it into a DC voltage output by using thermopiles. Since the fabrication process is fully compatible with the GaAs monolithic microwave integrated circuit (MMIC) process, this sensor could be conveniently embedded into MMIC. From the measured DC voltage output and S-parameters, the average sensitivity in the X-band is 225.43 μV/mW, while the reflection loss is below −14 dB. The MEMS microwave power sensor has good linearity with a voltage standing wave ration of less than 1.513 in the whole X-band. In addition, the measurements using amplitude modulation signals prove that the modulation index directly influences the output DC voltage.

Microwave frequency detector at X-band using GaAs MMIC technology

The design, fabrication, and experimental results of an MEMS microwave frequency detector are presented for the first time. The structure consists of a microwave power divider, two CPW transmission lines, a microwave power combiner, an MEMS capacitive power sensor and a thermopile. The detector has been designed and fabricated on GaAs substrate using the MMIC process at the X-band successfully. The MEMS capacitive power sensor is used for detecting the high power signal, while the thermopile is used for detecting the low power signal. Signals of 17 and 10 dBm are measured over the X-band. The sensitivity is 0.56 MHz/fF under 17 dBm by the capacitive power sensor, and 6.67 MHz/μV under 10 dBm by the thermopile, respectively. The validity of the presented design has been confirmed by the experiment.

Sensitivity of MEMS microwave power sensor with the length of thermopile based on Fourier equivalent model

A Fourier equivalent model is introduced to research the thermal transfer behavior of a terminating-type MEMS microwave power sensor. The fabrication of this MEMS microwave power sensor is compatible with the GaAs MMIC process. Based on the Fourier equivalent model, the relationship between the sensitivity of a MEMS microwave power sensor and the length of thermopile is studied in particular. The power sensor is measured with an input power from 1 to 100 mW at 10 GHz, and the measurement results show that the power sensor has good input match characteristics and high linearity. The sensitivity calculated from a Fourier equivalent model is about 0.12, 0.20 and 0.29 mV/mW with the length at 40, 70 and 100 μm, respectively, while the sensitivity of the measurement results is about 0.10, 0.22 and 0.30 mV/mW, respectively, and the differences are below 0.02 mV/mW. The sensitivity expression based on the Fourier equivalent model is verified by the measurement results.

Thermal time constant of a terminating type MEMS microwave power sensor

A terminating type MEMS microwave power sensor based on the Seebeck effect and compatible with the GaAs MMIC process is presented. An electrothermal model is introduced to simulate the thermal time constant. An analytical result, about 160 ms, of the thermal time constant from the non-stationary Fourier heat equations for the structure of the sensor is also given. The sensor measures the microwave power jumping from 15 to 20 dBm at a constant frequency 15 GHz, and the experimental thermal time constant result is 180 ms. The frequency is also changed from 20 to 10 GHz with a constant power 20 dBm, and the result is also 180 ms. Compared with the analytical and experimental results, the model is verified.

A novel symmetrical microwave power sensor based on MEMS technology

A novel symmetrical microwave power sensor based on MEMS technology is presented. In this power sensor, the left section inputs the microwave power, while the right section inputs the DC power. Because of its symmetrical structure, this power sensor provides more accurate microwave power measurement capability without mismatch uncertainty and temperature drift. The loss caused by the microwave signal is simulated in this power sensor. This power sensor is designed and fabricated using GaAs MMIC technology. And it is measured in the frequency range up to 20 GHz with an input power in the 0–80 mW range. Over the 80 mW dynamic range, the sensitivity can achieve about 0.2 mV/mW. The difference between the input power in the two sections is below 0.1% for an equal output voltage. In short, the key aspect of this power sensor is that the microwave power measurement is replaced with a DC power measurement.