CMOS微電容式超音波感測器

CMOS Micromachined Capacitive Ultrasonic Sensors

湯博凱(Po-Kai Tang)

指導教授 ： 盧向成

國立清華大學/工學院/奈米工程與微系統研究所/碩士(2010年)

https://doi.org/10.6843/NTHU.2010.00314

摘要

這項研究提出了一種可用於水中的超音波感測的CMOS微電容式傳感器。通過使用CMOSMEMS的技術，是可以將感測器與感測電路整合的。藉由CMOS製程，可有效降低電路的寄生電容，以提高信號的信噪比。藉由在感測薄膜下方放置感測電路，可以方便我們在製作大型的二維感測陣列的訊號拉線。
感測薄膜結構的釋放是藉由post-CMOS製程進行金屬蝕刻，而密封則是透過2微米的二氧化矽或是聚對二甲苯作為密封材料。單一的感測結構是由一直徑 60 微米的圓盤所構成，並形成一個34.8 fF的感測電容。而一個完整的感測器元件是由9個薄膜並聯，其總電容值為312.2 fF。
感測薄膜結構的釋放是藉由post-CMOS製程進行金屬蝕刻，而密封則是透過2微米的二氧化矽或是聚對二甲苯作為密封材料。此微結構是由直徑 60 微米的圓盤所構成，並形成一個34.8 fF的感測電容。一個完整的感測器元件是由9個薄膜並聯，其總電容值為312.2 fF。
在此我們施加一交流偏壓於感測薄膜的藉以穩定感測信號，否則由於介電質薄膜中的缺陷將捕捉電極間的電荷，造成感測信號隨著時間而減弱。通過這種交流偏壓量測法，在感測器和超音波發射器距離14毫米下，測得的訊號大小分別為456.1和683.5 mVpp。感測器在水中的共振頻率分別為8.8和6兆赫。

關鍵字

CMOS ； CMUT ； 電容式 ； 超音波 ； 傳感器

並列摘要

This work presents the CMOS micromachined capacitive sensors for ultrasound detection in water. By using the CMOSMEMS technology, the sensor combined integrated circuit is possible. The CMOS fabrication can effectively reduce the parasitic capacitance to enhance the signal to noise ratio. Convenient routing, which is desired for making large two-dimensional arrays, is achieved by placing the detection circuits beneath sensing membranes.
The sensing membranes are released by a post-CMOS metal etch and sealed by using either 2 um silicon dioxide or parylene-D . The microstructure has a suspended plate of 60 um in diameter that produces a sensing capacitance of 34.8 fF. The single detection element is formed by nine membranes with a total capacitance value of 312.2 fF.
An alternating voltage bias is applied to the membranes for stabilizing the sensed signals which would otherwise attenuate over time due to trapped charges between electrodes. By this method, measured signal is 456.1 and 683.5 mVpp with 14 mm between the sensor and the ultrasonic sound emitter. Resonant frequencies of the sensors in water are 8.8 and 6 MHz, respectively.

並列關鍵字

CMOS ； CMUT ； Capacitive ； Ultrasound ； Transducer

參考文獻

[1] G. S. Kino, Acoustic Waves: Devices, Imaging, & Analog Signal Processing. (Prentice-Hall, Englewood Cliffs, N.J., 1987).

[3] X. Jin, O. Oralkan, F. L. Degertekin, and B. T.Khuri-Yakub, “Characterization of One-Dimensional Capacitive Micromachined Ultrasonic Immersion Transducer Arrays,” IEEE Transactions on Ultrasonic, Ferroelectrics, and Frequency Control, Vol. 48, No. 3, May, 2001.

[4] A. Ballato, “Piezoelectricity: old effect, new thrusts,” IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 42, pp. 916-926, 1995.

[5] E. Fukada, "History and recent progress in piezoelectric polymers," IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 47, pp. 1277-1290, 2000.

[6] C. G. Oakley and M. J. Zipparo, "Single crystal piezoelectrics: a revolutionary development for transducers," Proceedings of the IEEE Ultrasonics Symposium , vol.2, pp. 1157–1167, 2000.