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

Abstract

The paper introduces a SU-8 dielectric µ-bridge based polymer MEMS Pirani gauge which can be employed for hermetic characterization of packaged electronic sensors. The µ-bridge structure is adopted due to its simplicity in fabrication and lower footprint, which makes it feasible for heterogeneous integration. Further, the integration of SU-8 polymer with the active thermistor offers superior thermal isolation from the substrate and extends the dynamic range. Before fabricating the actual device, the SU-8 based µ-bridge is optimized for stress-free release. A stress engineering is performed and thermal processing of SU-8 is optimized. The measurement results reveal that the removal of quenching from the baking steps leads to the successful fabrication of freely suspended µ-bridge with SU-8 polymer as a structural layer. A quantitative comparison of the proposed gauge is established by comparing the gauge performance with conventional dielectric materials like silicon dioxide (SiO2), silicon nitride (Si3N4), and aluminum oxide (Al2O3). The fabricated SU-8 polymer-based MEMS Pirani gauge with a 40 µm × 7 µm footprint can be used for hermetic characterization from 30 Pa to 105 Pa and is an ideal candidate for heterogeneous integration.

Electrostatically actuated all metal MEMS Pirani gauge with tunable dynamic range

“…Helium leak tests and Q-factor extraction techniques are employed to determine the pressure in micro-cavities [4][5][6]. However, their use is limited owing to the complexity and expensive procedures [6].…”

“…Helium leak tests and Q-factor extraction techniques are employed to determine the pressure in micro-cavities [4][5][6]. However, their use is limited owing to the complexity and expensive procedures [6]. More recently, micromachined Pirani gauges have been integrated with microsensors for fast, affordable, and accurate hermetic monitoring [7].…”

“…Lowering the solid conduction increases the gaseous conduction regime thereby extending the lower detection range. Also, materials with lower thermal conductivities materials were used to further reduce the solid conduction [6]. Lai et al presented a fusion study by integrating two Pirani gauges with different lengths [11].…”

Surface Micromachined CMOS-MEMS Pirani Vacuum Gauge With Stacked Temperature Sensor

“…To date, significant advances have been made in the research of micro-Pirani gauges, and a variety of different microstructure designs and sensing strategies have been proposed to improve sensor performance. Various sensing paradigms have been explored, including a sensor design that employs heat transfer between a vertically arranged microheater and heat sink, termed vertical heat transfer [4], [10], [11]. Similarly, sensor designs based on lateral heat transfer [12], [13], and hybrid vertical and lateral heat transfer [14] have also been reported.…”

“…Additionally, the performance of the Pirani gauge is also influenced by the number of heat sinks involved. However, most reported designs only incorporate one single heat sink [4], [10], [11], [12], while multiple heat sink designs necessitate more elaborate fabrication techniques [14], [17], [18], resulting in a reduction in sensor yield. Furthermore, in the prevailing research trend of multi-sensor integrated systems, there are very limited reports on integrated designs that combine vacuum gauges with other sensors [19].…”