建構式應力運用於CMOS-MEMS共振器傳感間隙窄化技術

Abstract

本論文研究在CMOS-MEMS 0.35 μm平台設計出一窄化共振器傳感間隙之結構，並成功將其縮小至奈米尺度。其中，透過彎曲梁結構的設計讓元件在濕蝕刻後，釋放結構中的殘餘應力並產生形變。從彎曲梁的中心點延伸並連接傳感電極，利用彎曲梁的形變帶動電極往共振器方向移動，進而縮小傳感間隙。 透過調整彎曲梁的尺寸參數能夠自由地改變形變量，並利用簡化數學模型以及有限元素法模擬彎曲梁的形變量，再設計初始的傳感間隙大小，可最佳化傳感間隙，突破製程上最小線寬之限制，甚至可使傳感間隙接近無限小或是輕碰共振器的狀態。並且過程中僅需經過一道濕蝕刻步驟便能完成間隙的窄化，不需施加任何的外力以及經過繁複的後製程步驟。 本研究亦將彎曲梁式電極分別運用於雙邊固定共振梁以及梳狀式共振器開關上。前者有效地縮小傳感間隙並以SEM量測到79.5 nm之間隙大小，並在直流電壓3.6 V下量測到394.5 kΩ的動態阻抗，與最小線寬之相同共振器相比，動態阻抗降低近157.4倍。後者同樣以窄化輸出端間隙，降低熱切換所需的最小驅動電壓，提升共振器開關之靈敏度。在直流電壓48.5 V下，僅以交流訊號電壓120 mVpp便能驅動元件成功熱切換。與一般共振器開關驅動訊號電壓的1.3 Vpp相比縮小約10倍。

This thesis presents a transducer gap-narrowing structure for resonators on 0.35-μm 2-poly-4-metal CMOS-MEMS platform. Particularly, an arc beam design releases the residual stress after wet etching and induce the deformation. The transducer electrode connected to the arc beam therefore moves toward the resonator and reduces the transducer gap spacing. The arc beam structure features high freedom of optimizing the gap spacing through modifying arc beam dimensions and the initial gap spacing. The simplified mathematical model and finite element analysis both assist the prediction of final transducer gap which below the design rule defined gap of 500 nm. Narrowing the gap spacing to infinitesimal or even tapping resonator exactly is possible. Moreover, the gap-narrowing procedure includes only one wet etching process. Additional force or complicated post fabrication process are unnecessary. This thesis practically uses the arc beam design on clamped-clamped beam (CC-beam) resonator and comb-driven resoswitch respectively. For CC-beam resonator, the arc beam electrode effectively reduces the transducer gap to 79.5 nm measured by SEM, and yields the motional impedance of 394.5 kΩ under DC bias of 3.6 V, about 157.4 times lower than 500 nm gap-spacing resonator of 62.1 MΩ. On the other hand, the resultant gap distance enhances the sensitivity of comb-driven resoswith and minimizes the actuate voltage by about 10 times, from 1.3 Vpp to 120 mVpp for hot switching under DC bias of 48.5 V.