利用殘餘應力於CMOS-MEMS微元件之設計與實現

Abstract

本論文提出以台灣積體電路股份有限公司0.35 μm標準CMOS製程整合微機電後製程之垂直式靜電致動微振盪器；在微加工製程中常見的殘餘應力 (Residual stress) 問題，本研究將之應用為正面的用途。此垂直式微振盪器為一複合材料懸臂樑，利用殘餘應力的不平衡使其在製作完成後產生翹曲的效果，如此使得設計在懸臂樑兩側之梳狀致動器其可動齒 (Movable finger) 與固定齒 (Fixed finger) 間具有高低差，當在梳狀齒 (Comb finger) 的兩極施加一電位差，即產生垂直方向的致動效果。此外，利用CMOS製程中的複晶矽做為壓阻元件，整合於懸臂樑結構中，感測微振盪器的靜態偏移與共振頻率；實驗得到當施加電壓100 V時其電阻變化率(ΔR/R)為0.52 %，遠較相關文獻所記載之變化率大，顯示其優良的壓阻特性。更進一步地，將梳狀致動器更改設計為多組電極形式，在不同的電極分別施予驅動電壓與箝制電壓 (Clamp voltage)，可使得微振盪器之共振頻率改變，達到調變頻率的目的。藉由不同電極組合搭配，得到28.5 %之最大頻率調變範圍，且此調變方式不損壞元件結構，具有高度應用價值。

This dissertation proposes a vertical comb drive resonator with electrostatic driving and piezoresistive sensing. The device is fabricated by the Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 μm two polysilicon layers and four metal layers (2p4m) complementary metal-oxide-semiconductor (CMOS) process and post-CMOS micromachining steps. Although the residual stress is a problem in most microstructures, it is utilized in the proposed device. The resonator consists of a composite beam and a set of comb fingers. One end of the composite beam is clamped to the anchor, and the other end is elevated due to the residual stress between the two deposited materials. The comb fingers are designed along the composite beam, and act as the movable and fixed comb fingers. When a voltage is applied between the movable and fixed comb, the movable composite beam can be pulled downward to the substrate vertically by the electrostatic force. A piezoresistor is designed to sense the vertical deflection and vibration of the resonator. The relative change in the resistance of the piezoresistor (ΔR/R) is about 0.52 % when a voltage of 100 V is applied in static mode. The result indicates that the piezoresistor possesses a good piezosistive characteristic. Furthermore, if the comb actuator is divided into several sets as multiple electrodes, the resonator can be driven under various conditions. The maximum frequency tuning range up to 28.5% is obtained and the resonator device can recover its original frequency without causing any structural damage.