The discrete vacuum packaging of IR-microbolometers

Abstract

Packaging of Micro Electro Mechanical Systems (MEMS) requires technical challenges to be solved and overcome when stringent vacuum and hermetic sealing is required. This is typical for a wide class of devices, such as inertial sensors, MEMS atomic clocks, IR micro-bolometers, where such conditions need to be achieved to provide the performance stability during the lifetime of the devices. The most challenging vacuum requirements are related to micro-bolometers, since good vacuum level is needed for thermal insulation. Typical target pressure is ≈ 10-3 – 10-4 mbar. Vacuum hermetic packaging can be successfully achieved by dedicated getter film integration, key technology for vacuum requirements, in combination with a specific sealing process and choice of vacuum compatible materials. The discrete packaging of the device requires the attachment of the sensing element into a ceramic package, like LCC. Typically, adhesives are used as die attach material. From the vacuum point of view, adhesives are not ideal candidates and therefore the compatibility with stringent vacuum requirements is not always guaranteed. Preliminary outgassing tests on these components are recommended to select appropriate materials. Thermal treatment of components is another key point for vacuum sealing, since specific degassing treatments before and during sealing can effectively reduce the amount of gas inside the volume of the device. The getter film integration is mandatory in such kind of devices because of the stringent vacuum requirements. SAES' proprietary technology is fully compliant with micro-bolometer manufacturing and the optimization of the getter activation step, during the bonding process, enables the functionality of the device along its lifetime. Moreover, capabilities of performing residual gas analyses and leak rate measurements of sealed devices are fundamental for quality control of vacuum sealing as well as for analyses and prediction of device lifetime.