Low-Temperature Au-In TLP Bonding for Compact Hermetic Packaging of Piezoelectric MEMS Devices

This study introduces a compact, low-temperature Au-In transient liquid phase (TLP) bonding-based packaging method for piezoelectric MEMS transducers with lateral feedthroughs. The packaging process uses silicon caps fabricated in a three-step process, while the Au-In bonding stack is designed to prevent premature intermetallic compound (IMC) formation. The transducers are fabricated on SOI wafers with low-temperature PECVD insulation layers, ensuring compatibility with piezoelectric material. The packaged transducer generates a peak voltage of 163.1 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{mV}_{\text{pp}}$</tex> under 0.1 g excitation at 570.9 Hz. The results demonstrate the effectiveness of the proposed method in achieving compact MEMS packaging while indicating that the sensor remains operational after packaging.