A Micromachined Reconfigurable Attenuator

Abstract

As the essential power control and adjustment component, microwave power attenuator has been widely applied in spectrum analyzer, network analyzer, receivers, and other microwave instrument systems. There has been significant interest in developing miniaturized microwave devices with small geometric dimension for commercial microwave test systems. Traditional attenuator with large size is difficult to integrate with IC due to its cumbersome mechanical relay or switches. Radio frequency microelectromechanical system (RF MEMS) switches present many advantages such as less insertion loss, higher isolation, better linearity, and lower power consumption and more importantly, its small size. It has absorbed great attention for the purpose of miniaturization of attenuator. Recent research shows step attenuator based on RF MEMS switches meet well the state-of-the-art requirements of miniaturized reconfigurable attenuation devices with high precision and broadband performance. In this chapter, we introduce a compact 3-bit step attenuator based on RF MEMS switches with 0~70 dB attenuation at 10 dB intervals up to 20GHz. The on-chip attenuator consists of 12 ohmic MEMS switches, 3 π-type resistive attenuation networks, and microwave compensate structures. To optimize the attenuation characteristics within the broadband, theoretical analysis and 3D modelling were performed. The device was obtained using MEMS process combined with polysilicon integrated circuit (IC) process. In section "Structure Design," the structure of the step attenuator was proposed and three modules were designed independently including: (1) Resistive attenuation network. Two approaches are presented and discussed. (a) Polysilicon thin film resistor with symmetric topology is applied to realize the high-precision π-type resistive attenuation modules (10, 20, 40 dB). (b) Distributed TaN single