Toward 2.5D Structures for Multi-Channel MEMS Acoustic-Based Digital Isolators using Through Silicon Openings.

In this paper, a piezoelectric MEMS-based digital isolator by the medium of air for transferring ultrasound waves between the transmitter (Tx) and receiver (Rx) is presented. A front-to-back 2.5-dimensional structure is also presented for assembling MEMS dice in the piezoMUMPs process. It is demonstrated that front-to-back stacking of dice is possible according to the thickness of layers in this process. This structure allows to minimize the distance between Tx and Rx, which is reduced and shows 43% improvement with the piezoMUMPS process compared to the conventional method. Also, it is explained that in the front-to-back bonding technique, there is only a need for top-side wire bonding. Through this process, it is possible to minimize the size of the final digital isolator by defining a waveguide utilizing a through silicon opening (TSO). Simulations show that according to the behavior of the sound wave inside the openings, the conical shape of the TSO has a direct effect on the transmission bit rate (improvement of 3.5 times) in contrast with the straight one.