Electromagnetic-Thermal-Electric Analysis of Indirectly-Heated RF MEMS Power Sensors With Different Terminal Resistor Dimensions

In this article, the design, fabrication and measurements are presented for an indirectly-heated RF MEMS thermoelectric power sensor with different terminal resistor dimensions. In this design, thermal isolation is achieved through a
$20~\mu \text{m}$
-thick MEMS substrate membrane using back etching technology. In order to maintain the stability of impedance matching, two low temperature coefficient of resistance (TCR) tantalum nitride (TaN) resistors of
$50~\Omega $
are adopted to serve as heating sources. Considering the effect of the terminal resistor dimension on RF power sensing performance, six configuration sensors have been explored experimentally. Experimental results show that the output response of these devices has excellent RF-DC linearity with the power from 1 mW to 200 mW. And as the dimension of the terminal resistor gradually increases, their sensitivities are
$77.3~\mu \text{V}$
/mW,
$63.4~\mu \text{V}$
/mW,
$56.3~\mu \text{V}$
/mW,
$54.4~\mu \text{V}$
/mW,
$49.5~\mu \text{V}$
/mW and
$47.9~\mu \text{V}$
/mW at 10GHz, respectively. Meanwhile, the measured response time is 3.2 ms, 2.9 ms, 2.7 ms, 2.5 ms, 2.2 ms and 2.0 ms, respectively. This indicates that as the size of the terminal resistor increases, the corresponding sensitivity and response time are decreasing. Therefore, there is a trade-off consideration between high sensitivity and fast response time. Further, an electromagnetic-thermal-electric model of the indirectly-heated RF MEMS power sensor is proposed based on the Seebeck effect and heat transfer theory. Experiments and finite element method (FEM) simulation are performed to verify the validity of the proposed model. The results would be useful to improve future sensor designs and specific applications.