The Research Of RF Mems Variable Capacitor

MEMS is the abbreviation of Micro Electrical Mechanics System. Since the requirement of small volume, high reliability and reduced cost in the personal commucation and military commucation, MEMS devices is also researched in RF field. Vibrating mechanical tank components, such as MEMS switch, MEMS inductance, MEMS variable capacitor, crystal and surface-asoustic wave resonators, MEMS resonators and filter, are widely used in commucation subsystems.Much high performance device is needed as the research of CMOS circuit is deeply performed in the current. The MEMS variable capacitor is a new device, which enable the more freedom in the CMOS circuit design and the realization in more reliability and higher integration. The following aspects of MEMS variable capacitor is researched in the article:The latest research development of variable capacitor is concluded and many new variable capacitors are given and compared. The purpose is to compare the current architecture of many capacitors to draw a conclusion which capacitor is high Q and can be easily made in the current process.The Crab beam capacitor is researched, including the initial capacitor, parasitical capacitor, tuning characteristic, displacement distribution, stress distribution, mechanical mode analysis. The"T"shape beam capacitor is presented on the basis including the initial capacitor, parasitical capacitor, tuning characteristic, displacement distribution, stress distribution same.The key manafacture process of capacitor is discussed which is the release of sacrifical layer and the dryness of the structure, Especially the selective etch of the Al and BPSG. The following dryness is also concern because the top plate will be pulled to the bottom by the surface tension. On the other, the top plate will wape by the thermal stress caused by the dryness heat.The high frequency characteristic and the test circuit is also discussed. The VCO's guideline and the characterisitic of Colpitts is also presented. The VCO consist of the capacitor is simulated and the simulated wave is also presented.