微機電音效薄膜之阻尼特性改良分析

Abstract

微機電電容式麥克風由於體積小與成本低，已廣泛應用在可攜式電子產品之中，然而其系統性能容易受空氣阻尼效應之影響，且在運用波紋結構以降低殘留應力時，也會使得系統之空氣層間隙不均勻而難以預測阻尼值。本研究運用擠壓膜統御方程式，結合具波紋結構之彈性音效薄膜，以建構有限元素分析模型，並透過理論之驗證，針對麥克風系統之三種物理場進行耦合分析。模擬結果顯示具波紋結構音效薄膜之空氣阻尼值會大於無波紋結構者；受殘留應力影響之薄膜亦會因為空氣間隙變小而使得空氣阻尼效應上升；此外，在波紋結構與薄膜中央處會產生最大的空氣阻尼壓力，因此在其下方背板處增加孔洞面積，即可有效改善微機電麥克風的系統性能。

Because of small size and low cost, MEMS microphones are prevalent in portable electronic devices. However, their system performance is significantly affected by air damping and the corrugated structure for residual stress reduction also leads to non-uniform damping effects. Based on the governing equations of squeeze film and MEMS flexible acoustic membrane with corrugated structure, the finite-element model of MEMS microphone system is constructed. The model is validated by theory and coupled multi-physics analysis is developed. According to simulation results, air damping of the acoustic membrane with corrugated structure is higher than the non-corrugated one. Change of the air gap by residual stress will increase air damping dramatically. Besides, maximum air damping pressure occurs under corrugated structure and the center of membrane. Therefore, enlarging the area of holes underneath can effectively improve the performance of MEMS microphones.