Innovative electro-structural integration approach defining large-area PMUT on TFT backplane for ultrasound imaging systems

We demonstrate an electro-structural integration approach to define piezoelectric micromachined ultrasound transducers (PMUT) on top of thin-film-transistor (TFT) backplanes for imaging applications, enabling large-area, low-cost transducer arrays. While the piezo stacks for these microelectromechanical structures (MEMS) are manufactured in a silicon foundry, the switches for element addressing are made separately using a standard TFT process, in a flat-panel-display fab. Cu/Ni/Sn microrings are processed on top of the piezo stack at wafer level, before a flip-chip assembly approach bonds a single thinned silicon die to the Ni/Au stack atop the TFT-on-glass die. The assembled devices are tested mechanically, electrically, and acoustically. A pulse-echo based 2D imaging demonstration is presented.