Low-stress photosensitive polyimide suspended membrane for improved thermal isolation performance

Abstract

In this paper, we introduce a method of isolating thermal conduction from silicon substrate for accommodating thermal-sensitive micro-devices. This method lies in fabrication of a low-stress photosensitive polyimide (PSPI) suspension structure which has lower thermal conductivity than silicon. First, a PSPI layer was patterned on a silicon wafer and hard baked. Then, a cavity was etched from the backside of the silicon substrate to form a membrane or a bridge-shape PSPI structure. After releasing, a slight deformation of about 20 nm was observed in the suspended structures, suggesting ultralow residual stress which is essential for accommodating micro-devices. In order to investigate the thermal isolation performance of the suspended PSPI structures, micro Pirani vacuum gauges, which are thermal-sensitive, had been fabricated on the PSPI structures. The measurement results illustrated that the Pirani gauges worked as expected in the range from 1– 470 Pa. Moreover, the results of the Pirani gauges based on the membrane and bridge structures were comparable, indicating that the commonly used bridge-shape structure for further reducing thermal conduction was unnecessary. Due to the excellent thermal isolation performance of PSPI, the suspended PSPI membrane is promising to be an outstanding candidate for thermal isolation applications.

Microfabrication of functional polyimide films and microstructures for flexible MEMS applications

“…In terms of thermal isolation, Fan et al introduced a method for isolating thermal conduction from a silicon substrate for accommodating thermally sensitive microdevices using a low-stress photosensitive polyimide suspension structure. Due to the excellent thermal isolation performance of PSPI, the suspended PSPI membrane is promising as an outstanding candidate for thermal isolation applications 144 .…”

Stress engineered SU-8 dielectric-microbridge based polymer MEMS Pirani gauge for broad range hermetic characterization

“…Since then, the trend of miniaturization and performance enhancement is active. Based on the architecture, MEMS Pirani gauges are classified into two categories [12] (a) bulk micromachined membrane-type; (b) surface micromachined µ-bridge type. Bulk micromachined membrane-type Pirani gauge consists of metal or poly-Si meandered thermistor resting on the dielectric membrane.…”

“…In contrast, the diaphragm-based structures require lower thermal conductivity materials to thermally isolate the thermistor from the substrate. Fan et al reported a polymer (polyamide)-based structure for better thermal isolation and reported a measurement range from 1 to 470 Pa [12]. Jeon et al presented a nanoporous anodic aluminum oxide-based structure for better thermal isolation [14].…”