PMN-PT Single Crystal Piezo-Electric Acoustic Sensor
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PMN-PT Single Crystal Piezo-Electric Acoustic Sensor Sung Q Lee, Hye Jin Kim, Sang Kyun Lee, Jae Woo Lee, and Kang Ho Park Nano Convergence Sensor Team, Electronics and Telecommunication Research Institute, 161 Gajeong-Dong, Yuseong-Gu, Daejeon, 305-350, Korea, Republic of ABSTRACT The MEMS (micro-electro-mechanical systems) microphone enables the manufacturing of small mechanical components on the surface of a silicon wafer. The MEMS microphones are less susceptible to vibration because of the smaller diaphragm mass and an excellent candidate for chip-scale packaging. In this paper, we present a piezoelectric MEMS microphone based on (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystal diaphragm. The PMN-PT materials exhibit extremely high piezoelectric coefficients and other desirable properties for an acoustic sensor. The piezoelectric-based microphone can offer the ability to passively sense without the power requirements. In particular, this paper introduces the design of a PMN-PT single crystal diaphragm with interdigitated electrode. We were able to fabricate miniaturized PMN-PT single crystal diaphragms. The fabricated sensor exhibits the sensitivity of 1.5mV/Pa. This implies that the PMN-PT thin film microphone has a potential of excellent acoustic characteristics.
INTRODUCTION As the telecommunication technology grows, a mobile terminal such as cellular phones requires a higher quality of images, videos, and sounds. Traditional electret condenser microphones (ECMs) have reached moderately small sizes. However, they are approaching the size limits and are unlikely to shrink much further. A new microphone technology, the MEMS (micro-electro-mechanical systems), enables the manufacturing of small mechanical components on the surface of a silicon wafer. The MEMS microphones are less susceptible to vibration because of the smaller diaphragm mass and thus an excellent candidate for chip-scale packaging. The MEMS microphones are widely investigated and promising in many areas, including consumer electronics, military and industrial uses. Recently several kinds of MEMS microphone technologies have been proposed, such as condenser [1-4], electret [5,6], piezoresistive [7-9], photo-acoustic [10], and ferroelectric microphones [11-12]. However, condenser and ferroelectric microphones are popular ones due to their excellent performances. In the case of condenser microphones, a back plate and a diaphragm are built on the surface of a wafer along with the necessary electrical connections. The diaphragm is chemically etched so it can vibrate freely with incoming sound. The changing capacitance of the charged capacitor formed by the back plate and diaphragm changes acoustic signals into electrical signals. It is also known that the type of microphones requires relatively high bias voltage and has a limited sound frequency range. The condenser microphones show the highest sensitivity among all candidates. However they suffer a fabrication complexity in forming a narrow air-gap between two comparatively large
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