Vibration analysis of pMUT with polymer adhesion layer

Wafer bonding using polymer adhesive layer has gained many attentions for various MEMS applications. Numerous techniques and processes that utilize polymer adhesive have been established recently, mainly for wafer bonding and device packaging. However, adhesive layer contribution in vibrating micro structure such as micro ultrasonic transducer requires further investigations. This paper reports performance difference of piezoelectric micro ultrasonic transducer (pMUT) with polymer adhesion layer of PDMS, Cytop and Polyimide. Finite element analysis was utilized to analyze structure behavior during vibration. Frequency analysis revealed 41 kHz shift in device´s resonant frequency when different type of polymers employed as adhesive layer. Further investigations through piezoelectric analysis found that PDMS has contributed in 40% decrease of voltage response than other two polymers at only 6×10^-5 μm/V, but carry the highest stress response at 2×10^-5 μm/Pa in both transmit and receive modes in mechanical analysis. Finally, same analysis cycle was conducted on pMUT structure with polymer adhesive layer being replaced by polysilicon at the same thickness.