On-wafer PDMS micropatterning via etch-back lift-off and its application to MEMS microactuators

Polydimethylsiloxane (PDMS) is a versatile material used in microsystems due to its biocompatibility, optical transparency, and flexibility. However, existing PDMS micropatterning methods face challenges such as poor reproducibility and limited compatibility with traditional MEMS wafer fabrication processes. To address these limitations, we propose the etch-back lift-off (EBLO) method, a precise on-wafer PDMS micropatterning technique. The method enables micron-scale resolution, excellent vertical sidewalls, and minimal surface roughness. The EBLO method was validated on a 4-inch silicon wafer, producing PDMS structures with feature sizes of 4 µm and above that maintained structural integrity for aspect ratios below 2.8. The overall PDMS thickness uniformity was measured at 3.0 %, and surface roughness R a increased only slightly from 0.26 nm to 0.82 nm after 10 min of reactive ion etching (RIE). To demonstrate the applicability of this method, a piezoelectric MEMS microspeaker was fabricated using PDMS patterns for damping and air sealing. Compared to a reference structure without PDMS, the device exhibited improved frequency response flatness and a significant reduction in total harmonic distortion (THD), decreasing to 13 % at f 0 /2. These results show the EBLO method as a robust and scalable platform for PDMS integration in MEMS devices, with potential for high-precision microsystem and bio-integrated applications.