Hermetic Sealant Material Possibilities for IR Sensor Packaging

Hermeticity is one of the most critical issues for infrared (IR) sensor packages, since any leakage will impair the functionality of the device. The issues associated with the premature failure of hermetic sealants were studied in detail, both by simulation as well as by experimentation. Alternate prospective hermetic sealant candidates for transistor outline IR sensor packages were identified and evaluated. Hermetic sealant options for wafer-level IR sensor packaging were also investigated, which involves wafer-level hermetic cum vacuum packaging. Metallic hermetic sealant is preferred for this approach, since it facilitates integration with the getter material. However, the primary challenge encountered here is the requirement of high processing temperature for the getter activation. An activated getter adsorbs active gases inside the volume of the packages, resulting in lower internal pressure. It was determined that appropriate micro-alloying of the getter is required to minimize the getter activation temperature. This is achieved by selective micro-alloying of the getter material, which induces more grain boundaries and thereby promotes in-depth diffusion even at lower activation temperature. Integration of getter material with all three different types of metallic wafer-level bonding mechanisms was investigated. This includes eutectic, diffusion and transient liquid-phase bonding mechanisms. Selection of an appropriate bonding mechanism and integration scheme depends on the corresponding structure, layout and temperature rating of the specific IR sensor devices.