使用低功耗振盪器讀出電路之 CMOS MEMS電容式超音波感測系統

A CMOS MEMS Capacitive Ultrasonic Sensor System with a Low-Power Oscillator-Based Readout Circuit

王惠君(Hui-Chun Wang)

指導教授 ： 蔡宗亨

國立中正大學/工學院/電機工程學系/碩士(2015年)

摘要

本論文實現一個以CMOS MEMS方式製作的電容式超音波感測系統，並搭配弛張型振盪器接收感測訊號，將感測訊號振幅轉換為頻率變化，可用於亮度模式呈現超音波影像，簡化一般超音波感測系統以轉阻放大器讀出前方感測訊號後，再以類比數位轉換器將超音波感測訊號轉換為數位訊號，利用振盪型讀出電路放大訊號後並達到初步的數位訊號轉換，以降低整體系統功耗。
此超音波感測系統將感測器與感測電路完全整合於同一晶片中，全晶片以標準CMOS製程TSMC 0.35μm 2P4M製作完成，晶片為面積3.5mm2，以此CMOS MEMS方式完成晶片能降低額外寄生電容與雜訊來源，提高系統解析度，並且結合濕蝕刻後製程完成感測器之懸浮結構，另外全晶片考量防水封裝，以微小化晶片呈現，可應用於醫療手術中作為導管內視鏡，取代光學影像在液體中成像模糊之缺點，抑或使用在可攜式超音波系統中，縮小探頭體積。在3.3V的電壓供應下，全系統功率消耗為0.56mW，讀出電路的靈敏度為289Hz/nA。

關鍵字

弛張型振盪器 ； CMOS MEMS ； 電容式超音波感測器 ； 微機電系統 ； 振盪型讀出電路

並列摘要

The thesis presented a capacitive ultrasonic sensor system fabricated by CMOS MEMS method. Nevertheless, the sensing signal is received by the relaxation oscillator to transfer the amplitude of the signal to frequency variation. In this way, the ultrasound image can be presented in Bright-mode(B-mode). The ultrasonic sensor system can be simplified design without using an explicit analog to digital convertor, in order to achieve a low power system.
The ultrasonic sensor and the sensing circuit is integrated in a single chip by standard CMOS process of TSMC 0.35μm 2P4M and the area of whole chip is 3.5mm2, that can decrease the parasitic capacitor and the noise to increase the resolution. The suspend structure of the sensor can be completed by post process using wet etching method. The capacitive ultrasonic sensor and be applied in medical region for the guide of the catheter because the whole chip is considered in water proven package and minimize the size as a chip. This can compensate the drawback of the optical image has in the blurred liquid. This ultrasonic sensor system can also used in the portable ultrasonic system. The total power consumption of the whole chip is 0.56mW and the sensitivity of the oscillator based readout circuit is 289Hz/nA.

並列關鍵字

relaxation oscillator ； CMOS MEMS ； capacitive ultrasonic sensor ； MEMS ； oscillator based readout circuit

參考文獻

[1] D. Spoliansky, I. Ladabaum, and B.T. Khuri-Yakub, "Micromachined ultrasonic air transducers (MUTs)," Microelectric Engineering, vol. 30, pp. 535 - 538, Jan. 1996.

[2] A.S. Ergun, Y. Huang, X. Zhuang, O. Oralkan, G.G. Yarahoglu, and B.T. Khuri-Yakub, "Capacitive micromachined ultrasonic transducers: fabrication technology," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 52, no. 12, pp. 2242- 2258, Dec. 2005

[5] A. Manbachi and R. S.C. Cobbold “Development and Application of Piezoelectric Materials for Ultrasound Generation and Detection.” Ultrasound vol. 19 no. 4 pp.187–196.Nov. 2011

[6] A. Ballato, “Piezoelectricity: history and new thrusts.” Proc. of IEEE. Ultrasonics Symposium., vol. 1., 1996.

[7] G. K. Fedder, R. T. Howe, T.-J. K. Liu, and E. P. Quevy, “Technologies for cofabricating MEMS and electronics,” Proc. IEEE, Jan. 2008, vol. 96, no. 2, pp. 306–322.