Batch-compatible micromanufacturing of a CMUT array for optoacoustic imaging of tissue-like phantoms

Abstract

Photoacoustic imaging (PAI), also named optoacoustic imaging, is a technol-ogy for medical imaging that relies on contrast data due to optical stimulation. Capacitive micromachined ultrasound transducers (CMUTs) are previously in-troduced for PAI applications. In this thesis, the provided CMUT array design has been partially micro-manufactured separately from electronics and a laser fiber light source while re-serving the necessary chip space for integration with electronics and laser fiber light source. Batch compatible wafer-scale microfabrication of CMUT arrays was done by a combination of novel as well as traditional MEMS microfabrication pro-cesses. CMUT array gaps, bottom electrodes, and insulation layer were formed on the Pyrex wafer using three separate photolithography masks. Anodic wafer bonding method is used for the formation of the top electrodes and top side of the gap heights of CMUT arrays. Process development for anodic wafer bonding between Pyrex wafers and SOI wafers has been done, where the Pyrex wafers have been previously processed with plasma etching, wet etching, metal stack de-position, insulation layer deposition, and insulation layer patterning, while SOI wafers have been used as received. Pyrex wafers and SOI wafers were anodically bonded to each other with developed anodic wafer bonding processes. After full completion of the micromanufacturing of the CMUT array chips, these CMUT ar-ray chips will be integrated with ASIC chips. Then, CMUT array chips and ASIC chips will be combined with a traditional printed circuit board (PCB). These in-tegrated CMUT array chips, ASIC chips, and PCB are going to be integrated with a fiber laser light source inside a mechanically robust hand-held probe that is planned to be used for optoacoustic imaging. The main goal of this CMUT array micromanufacturing study is to significantly contribute to the development of one of the necessary components for imaging of a tissue like-phantom using a hand-held imaging probe.