微機電系統是現階段被廣泛應用於感測元件的開發應用，因為它有微小化，整合系統晶片及適用於半導體製程的優點。然而由於大部分結構均為可動機械元件，在反復的操作下，雖然形變較小應力較低，但由於循環負載次數過多，其相對應所產生的疲勞破壞就極為可觀。此一破壞模式為現今微機電相關產品所面臨的極大挑戰，因為它往往會讓產品無法有良好的妥善率和惡劣環境的適應性，並且無法通過各種終端產品的可靠度測試。以常見的運動感測器為例，如加速度計(
Accelerometer)或是陀螺儀(Gyro)，它們往往均應用彈簧結構連結相對應的質量塊，彈簧連動模式又可分為彎矩和扭曲兩種，當質量塊受到加速度或是角加速度而有位移時，就會牽引彈簧產生變形，雖然此形變值往往都比較小，但反覆週期過多時，應力集中處就有可能發生斷裂，而造成整個元件毀壞。
本研究將著重於受扭矩負載下之微機電結構的高周疲勞特性研究。力求發展出高周疲勞破壞的有限單元之預測方法，針對受扭矩負載下的微機電結構提出相對應的壽命預估公式。分析高周疲勞可由基礎之力學理論出發，配合適當之研究設計方法及實驗驗證，找出所使用材料的相關應力-週期曲線（S-N curve）。故而確定本研究研究方法為模擬與實驗相結合，透過有限元素法對問題進行分析。
在本研究初期首先完成了文獻回顧，查閱了大量已經發表的論文和已經出版的書籍，確定了對於高周疲勞壽命的預測多會用Basquin公式對實驗資料進行擬合。而針對於微機電結構中的主要構成材料矽來講，其破壞準則將會採用最大主應力來進行判別。本研究首先將會確定對於微機電結構進行模擬時所用的網格密度大小，進而對已存在較完整實驗資料的論文進行模擬驗證，從而試著找出適用性較強的壽命預估公式。另外，由於對微機電結構施加負載的方式分為固定位移負載和固定外力大小負載兩種，而在固定外力大小進行負載施加時不同的負載頻率可能會產生不同的位移大小及應力大小，本研究也會進行進一步的探討。

Microelectromechanical Systems (MEMS) has been widely applied for many sensor applications. It can be miniaturized and integrated into standard CMOS process. But most of the MEMS structures are moveable and easily to generate large deflection and stress under some serious loading. This stress often induces some structure fatigue when the loading applied in many cycles. It impacts the reliability quality of MEMS products and damage the micro structure easily in harsh environments. For example, the motion sensor accelerometer and Gyro always combine moveable mass part and bending or torsion spring, which change their shapes severely under some large acceleration or angular acceleration. After many cycles of this deformation, the spring structures will be damaged and cause the device failure.
In this research, we will focus on the high cycle fatigue characteristics of Silicon-based Micro Structure under torsion loading. I will try my best to develop high cycle fatigue prediction with stress evaluation by finite element method. Provide the prediction equations of life cycles for pure torsion beam at MEMS devices. Based on the theory of mechanics, we can analyze the high cycle fatigue and find out the related material stress-cycle curve with appropriate methods of research design and experimental verification. Therefore, this research method is Combine simulation with experiment. Through the finite element method to analyze problems
At the beginning of this study, a review of the literature was completed, and a large number of published papers and published books were reviewed. It was confirmed that the Basquin formula was used to fit the experimental data for high cycle fatigue life prediction. For the main constituent material in the micro-electromechanical structure is silicon which is a kind of brittle material, the failure criterion will be judged by the maximum principal stress.
This study will first determine the element size of the MEMS finite element model. And then use the element size to other papers which have complete experiment data to get a simulation result and a better S-N curve. Finally, try to find a life prediction formula which has better applicability.

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