Micromechanical Tunable Capacitors for RF Applications

• Main Authors: Shih-Chieh Lin, 林士傑
• Other Authors: Ching-Liang Dai
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/76959270192509411570

碩士 === 國立中興大學 === 機械工程學系所 === 95 === The fabrication of micromachined tunable capacitors using the standard 0.35 μm CMOS (complementary metal oxide semiconductor) process and a post-process have been implemented. The tunable capacitors have the advantage of large tuning range. The simulated results show that the tunable capacitor can achieve a tuning range of 154%. Structure of the tunable capacitor is composed of a movable electrode plate, three stationary electrode plates and supported beams. The tunable capacitors require a post-process to etch the sacrificial layers, and to release the suspended structures consisting of the movable plate and beams. The sacrificial layers are silicon dioxide. The post-process uses silox vapox etchant to etch silicon dioxide to release the suspended structures in the tunable capacitors. Finally, the vector network analyzer is employed to measure the performance of the tunable capacitor. Experimental results show that the tunable capacitors have a tuning range of about 85% with a bias of 21 V and a Quality factor of 39.6 at 0.1 GHz. The study also presents a novel liquid crystal tunable capacitor using the CMOS-MEMS technique. The advantages of the tunable capacitor are small area and large tuning range. The tunable capacitors contain a driving electrode and a sensing electrode. The dielectric of liquid is changed when applying a voltage to driving electrode, leading to the tunable capacitor changes in capacitance.