Micro Capacitive Transducer for Air-Coupled and Phase-Controlled Ultrasonic Inspection
Final Report Abstract
The research project has been focused on the development of an air coupled, phase controlled micromachined ultrasonic transducer (MCT). During the research project, two technological approaches for the fabrication of these devices are proposed. Furthermore, a composite membrane consisting of different layers had been analyzed, to minimize the tensile stress inside vibrating membrane as well as to miniaturize the transducer arrays. A significant increase of the intrinsic stress inside the membrane can be observed, when annealing the stack to the bonding temperature of the devices. Adjusting the layer code by integrating additional silicon oxide layers with compressive stress, the overall intrinsic stress inside the membrane can be significantly reduced, enabling the fabrication of miniaturized MCT devices. Furthermore, two TSV technologies for the integration of vertical interconnects in micromachined ultrasonic transducers have been analyzed, enabling vertical interconnects between front and backside with a small resistivity of less than 2 Ω. A surface micromachined MCT device is processed within the project. Further effort will be required in the field of characterizing this device as well as increasing the homogeneity and reproducibility of each process step. None the less, the proposed technology might mark the first step towards an industrial application of the obtained results, focusing on miniaturized ultrasonic transducers for material analysis and medical applications.
