微機電揚聲器目前普遍受限於微縮的元件尺寸，面臨輸出聲壓不足以及操作範圍受限的問題。本研究以高聲壓等級與大操作頻率範圍為兩大目標，透過SOI製程設計並實現壓電式微機電揚聲器，藉由高壓電係數的PZT壓電薄膜，搭配彈簧、振膜與電極的設計，提升振膜的出平面位移、激發特定的共振模態，達到更高的聲壓等級以及更大的操作頻率範圍。通以2 Vpp的驅動電壓，在標準的人工耳系統內量測，雙彎曲式彈簧設計展現了很好的低頻表現，相較於傳統的封閉式振膜，在1 kHz處的聲壓等級提升了18.1 dB；單彎曲式彈簧搭配中央驅動電極的設計則是將聲壓等級60 dB以上的頻率範圍延伸至15.0 kHz，頻率範圍比單純的單彎曲式彈簧結構增加了4倍以上；單彎曲式彈簧搭配肋補強振膜的設計則是將聲壓等級60 dB以上的頻率範圍延伸至6.78 kHz，同時擁有極佳的低頻表現，1 kHz處的聲壓等級高達84.0 dB。此外，本研究之振膜面積相較於已發表之壓電式微機電揚聲器微縮了9倍以上，但仍保有極具競爭力的聲壓等級。

Limited by the miniaturized chip size, current MEMS microspeakers suffer insufficient sound pressure level and frequency range. This study aims to design and realize piezoelectric MEMS microspeakers with high sound pressure level and broad frequency range by means of the SOI processes. On the basis of high piezoelectric coefficient PZT thin film, the designs of spring, diaphragm, and electrode enhance out-of-plane displacement of diaphragm and actuate specific resonant modes to get higher sound pressure level and broader frequency range. Measured in the standard ear simulator systems with 2 Vpp driving voltage, the results show that: the dual-curve spring design has good performance at low frequencies, and the sound pressure level is 18.1 dB higher than the clamped type; the design of single-curve spring with central driving unit extends the frequency range higher than 60 dB to 15.0 kHz, and the range increases more than 4 times compared with the single-curve spring design; the design of single-curve spring with rib-reinforced diaphragm extends the frequency range higher than 60 dB to 6.78 kHz, and has nice low-frequency performance with 84.0 dB at 1 kHz. Moreover, compared with the published literature of piezoelectric MEMS microspeaker, the diaphragm area of this study is more than 9 times smaller while the devices still show a reasonable sound pressure level.

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