Research On RF MEMS Switches Based On LCP Substrate

With the rapid development of wireless communication technology and the rapid increase of communication frequency, the research on electronic devices for high frequency communication applications has become a focus of electronic communication industry's concern. With its excellent microwave properties such as high linearity and low insertion loss, RF MEMS received wide attentions from the field of radio frequency devices. In particular, RF MEMS switches have low insertion, high isolation, linear characteristic and low power consumption and they have been the prime candidates to replace the conventional GaAs FET and p-i-n diode switches in RF and microwave communication systems. At present, the most RF MEMS switches are manufactured on silicon substrate or GaAs substrate. MEMS process has poor compatibility with traditional IC process and the cost of MEMS devices based on silicon or GaAs substrate can be high. However, liquid crystal polymer (LCP) has very low water absorption, low dielectric loss, low cost and multi-layer circuit capability make it very appealing for RF systems-on-package (SOP). Furthermore, LCP is a flexible material, RF MEMS devices and RF circuits based on LCP substrate will be very suitable for systems with high space requirements and wearable devices, etc.This paper studies on RF MEMS switches based on LCP substrate and the effect of substrate bending on mechanical properties of switches. This paper does lots of research on the principle, classification and study of the current situation and the basic concepts of RF MEMS switches. On this basis, this paper completes the following work:1. Through the basic principle and design theory of RF MEMS switch and the driving mechanism, the structure of RF MEMS switch is designed. In this paper, two kinds of RF MEMS switch based on LCP substrate are proposed. They are electrostatic driven switch and thermal driven switch.2. Due to the requirements of mechanical and microwave properties of the switches, the microwave and mechanical structure of the switch are simulated and optimized. In order to achieve high isolation and low insertion loss of the electrostatic driven switch, the switch structure is optimized to reduce the coupling capacitance. For the thermal driven switch, the cantilever is optimized to match the requirements. For the mechanical structure of the switch, in order to make the electrostatic driven switch have smaller driving voltage, spring like structure is used in the switch. In order to make the trermal driven switch have a great driving force and displacement, V-shaped actuator is optimized. In addition leverage principle is used in the switch.3. The switch proposed by this paper is fabricated and the switch is tested and analyzed using Agilent N5244A VNA-X and cascade Probe station. The test results of the electrostatic driven switch show that the pull-in voltage of the switch is about 22V, the insertion loss is better than-0.6dB at 20GHz, the isolation is better than-15dB at 20GHz; The actuated curret of the thermal driven switch is about 0.8A, the insertion loss is better than-1.5dB at 10GHz, the isolation is better than-30dB at 10GHz. With the increase of the bending degree of the substrate, the pull in voltage increases first and then decreases. It is in good agreement with the theory.MEMS devices or RF circuits based on LCP flexible substrate can be applied to systems with high space requirements and wearable devices. There is a great potential in the civil field.