CMOS-MEMS電容式零偏壓微型陣列超音波換能器開發與生醫成像系統應用

Abstract

本研究利用TSMC 0.35μm 2P4M CMOS-MEMS製程製作電容式微機電超音波換能器(Capacitive Micromachined Ultrasonic Transducers, CMUTs)，並基於先前單元件CMUTs與零偏壓操作的研究成果，開發微型陣列超音波換能器，並將之應用於生醫超音波成像。 本論文將先簡介元件結構的設計、製程過程、良率改善的成果與電荷累積模型的運用。元件結構的部分沿襲過去研究，並在製程流程上調整改進，跟過去製程相比減少一半所需的時間。此外利用電荷累積模型建立CMUTs驗證的步驟，排除因離子汙染或是薄膜特性缺陷造成無法收發訊號的問題，更配合電荷累積模型提升元件的收發性能，在相同量測條件下提升約1.9倍訊號雜訊比，並盡可能將同一晶片不同元件間效能達到一致，也針對CMUTs進行多種性能量測，了解CMUTs訊號穿透深度與訊號衰減的情形，以上測試建立CMUTs陣列超音波換能器完整的性能資訊。 本研究同時著力於陣列超音波換能器的開發，配合國研院晶片中心(Chip Implementation Center, CIC)提供之PCB板製程服務，研究成果包含開發12MHz的CMUTs陣列元件以及與晶片搭配之雙面硬式電路板的設計與封裝，製作出陣列超音波換能器的原型，並成功繪製B-mode影像且進行分析，以期成為傳統商用壓電探頭的替代選項。

In this study, a phased-array of zero-bias CMOS-based Capacitive Micro-machined Ultrasonic Transducers (CMUTs) with high sensitivity is developed. The device is implemented with the TSMC 0.35µm 2P4M CMOS-MEMS process. Based on the previous research at the CMUT cell and zero-bias operation, this thesis presents a successful achievement on the development of 12 MHz phased-array CMUTs and its application in biomedical imaging. The thesis will first introduce the CMUTs design and the improved post CMOS process of fabrication, which can significantly enhance performance and the yield of CMUTs. The improvement of post CMOS process includes changing previous process steps to speed up fabrication and verifying CMUTs by I-V scan. Besides, the characteristic of CMUTs’ performances based on transmit signal, receive signal, pulse-echo signal, SNR ratio, penetration of depth, and attenuation-time curve were studied and analyzed in this thesis. The performance enhances 90% compared to previous works. Last but not least, the thesis will present the prototype of CMUTs tube package and its B-mode scanning imagines. These detail analyses provide necessary and vital information for the future application of CMUTs.