Piezo MEMS characterization and packaging

With the introduction of MEMS miniaturization technology a new class of ultrasound transducers i.e. micro machined ultrasound transducers (MUTs) is promising to overcome the short comings of the conventional transducers. These MUTs represent a novel approach to ultrasound generation and detection and the same principle is being used in our wearable ultrasound devices. Such MUTs are the subject matter of this investigation. The report deals with the characterization of MEMS devices resulting in the optical and electrical data on their performance. The characterization results show a variation of 20% in resonance frequency and an order of magnitude in displacement. Irregularities in MEMS device processing resulted in such large discrepancies. But these results lead to the recommendations regarding the preferable type of devices for future analysis. MEMS devices with slits are preferred over closed membrane devices due to the consistency in their vibrational characteristics. It is also believed they are capable to handle the pressure exerted during moulding when performing the packaging unlike closed membranes. Further, based on the discussions with suppliers two packaging flows, one for industrial production and another for in-house experimental processing, are proposed. PDMS is chosen as a suitable material for in-house trails due to its biocompatibility and material properties matching the packaging requirements. For low volume industrial production a suitable packaging concept is designed after consulting MEMS packaging companies. With respect to packaging, at this moment wire bonding of MEMS devices is complete and PDMS overmoulding of devices is in progress.