Vacuum Packaging of MEMS-based Infrared Detectors

MEMS-based infrared sensor is a key component in thermal cameras. Vacuum wafer-level packaging is a cost-effective process to ensure proper functionality of such sensors over its long lifetime. This paper presents our recent work in the process development of the vacuum wafer-level packaging for a large sensor array covering an area > 100 mm², Cu-Sn solid-liquid interdiffusion bonding was used for the hermetic sealing. A seal frame design with 3 rails showed 60% reduction in average Sn squeeze-out distance compared to a continuous seal frame. Successfully vacuum sealed sample with 300 µm thick Si cap provided mechanical stability and measurable cap deflection for a 12 mm × 12 mm die area. Cap deflection measurements of a sealed wafer sample show 14 out 19 dies retain the initial vacuum level after 8 months since bonding. Various challenges in obtaining the vacuum sealing of large dies at wafer-level are also discussed.