Uncooled IRFPA with chip scale vacuum package

We have developed an uncooled IRFPA with a chip scale vacuum package and succeeded in obtaining excellent IR images of less than 60 mK in NETD. This package consists of a device chip and a silicon lid. The chip in this study is a 160 x 120 SOI diode IRFPA with a 25 μm pixel pitch. The size of the package is 14.5(L) x 13.5(W) x 1.2(H) mm. The gap between the device chip and the lid is controlled by the thickness of the vacuum sealing material. The lid is prepared by a wafer process and diced just before vacuum sealing. We use DLC (diamond like carbon) as the AR coat because of its high IR transmittance and high endurance in the wafer process. DLC films are deposited on both sides of the silicon lid wafer, and then a ring-shaped metal pattern for solder bonding is formed on one side of the lid wafer. Solder is mounted on the metal pattern by a molten solder ejection method. The patterned thin-film getter is formed on the lid wafer. Because of the use of patterned thin-film getter, there is no need to form a cavity on the lid to allow installation of getter or to insert a spacer between the device chip and the lid. Then the lid wafer is diced into individual lids. The device wafer and the lids are set in a vacuum chamber, which has a heater to melt the solder, so as to pair each die and lid. After pumping the chamber, the patterned thin-film getters are activated and then the lids are bonded simultaneously to the device wafer. Finally the device wafer is diced into individual chips. The measured pressure of the package is less than 0.5 Pa which is sufficient for obtaining high thermal isolation. In this technique, only the good dies in a wafer are packaged in chip scale simultaneously. Thus, a reduction in the size and cost of the package has been achieved.