以多晶矽製程帄台研發與改良電容式微加速度計

Abstract

本論文研究重點為致力於先前所提出對稱式線圈型懸吊雙軸微加速度計之可運作率的提升。而可運作率的定義即為我們所製作之元件的可動率來判斷，並藉由結構設計與製程參數來提升之, 此外亦討論並解釋了實驗與模擬之共振頻率的不同, 而亦針對加速度計常見的耦合問題進行了量測與探討〃 結構設計上，使用差動式感測懸臂來作電容的感測，且沿用對稱懸吊結構。在應力殘留與可動率上仍有改進空間，本研究改進製程參數、增加懸吊剛性以及提高質量塊高度來改善問題。在退火參數950°C20sec，並將懸吊線寬由1.6μm改為1.86μm，質量塊高度由2μm提升為3μm的情況下，能使整體可動率提升高達85%以上。 在共振頻率量測上，過去的研究工作顯示實驗值與模擬值最大有20%的差異，本研究在量得實際懸吊尺寸後重新進行模擬，得以驗證此誤差在合理範圍內。 電性輸出量測方面，耦合問題為開發單一質量塊加速度計常遇到的問題，本實驗室所開發之加速度計提出以對稱結構設計來盡量減少耦合，但仍易因其他原因導致耦合效應。因此本研究藉由實驗與模擬，得到懸吊不對稱性對兩方向之耦合的影響。此外在不同電路工作頻率的下，發現到靈敏度與耦合度皆會受其影響，但趨勢尚無一致性，原因尚待探討。

This thesis focuses on the improvement on the yielding of previously proposed two-axis micro-accelerometer with symmetric coil-type suspension. The yielding is defined as the movable rate of the proof mass. To improve the yielding of the accelerometer, the suspension dimension is redesigned and the annealing parameters are modified. The differences between the experimental and simulated results are also investigated, including resonant frequency and coupling effect. In this micro-accelerometer, the differential capacitance sensing cantilevers and symmetrical suspension structure are utilized. The width of the suspension structure is increased from 1.6 μm to 1.86 μm, and the suspended gap is increased from 2μm to 3μm to have larger structural rigidity. With 950 °C annealing for 20sec both approaches as shown to increase the yielding more than 85%. For the resonant frequency, there was 20% difference between experimental and simulated results. After using the measured sizes of the suspension, and calibrated Young’s modulus, the current results of measured resonant frequency is shown to agree with the simulation results. For the coupling effect, the developed accelerometer utilized symmetrical design to avoid the coupling effect, but coupling between two axes still can be observed. It is found that the asymmetry of the suspension dimensions and input electrical signal frequency are two reasons. However, the reason of working frequency to affect coupling effect needs to be further investigated.