An infrared (IR) transparent window is necessary for the IR sensor package. The most commonly used materials for IR transparent window are germanium (Ge) and silicon (Si). Ge has excellent optical properties but also the disadvantage of expensive price. Si has merits such as inexpensive cost and CMOS process compatibility but it has lower transmittance in the range of LWIR region than Ge. Therefore, an alternative anti-reflection (AR) coating is necessary to increase the transmittance of Si as an IR transparent window in the LWIR region. A simple single layer antireflection coating was newly designed on the silicon window for the infrared sensor package. Among the various materials, nickel oxide (NiO) was selected as an AR coating material due to its suitable optical properties and simple process. NiO film was deposited onto the double sided polished Si wafer by reactive rf sputtering with Ni target in an environment of Ar and O2 mixed gas. The thickness of the NiO film was determined by Essential Macleod simulation. FT-IR was used to measure the transmittance of the samples in the LWIR region. After the nickel oxide film was sputtered onto the double sides of the silicon wafer, the measured transmittance of the Si wafer was increased over 20% in the LWIR region compared with that of uncoated Si wafer. Additionally, annealing effect on the transmittance of NiO coated Si wafer was studied. By increasing the annealing temperature from 300° to 700°, an additional increase of transmittance was achieved.
During microbolometer operation, the detector occasionally views high temperature scenes such as the sun or
flames at very close distance. The detector temperature can then increase to a level so high that the sensing material
experiences an annealing effect. Accordingly, the microbolometer is required to stand high temperatures that can cause
In this paper, a bimorph leg integrated microbolometer structure is proposed. The bimorph leg is an extra leg that
is separated from the signal transfer legs. It is bent downward and snaps onto the substrate when the microbolometer's
temperature reaches a critical temperature. The temperature of the micro-bolometer is then decreased as heat is
transferred to the substrate.
By snapping the bimorph leg down onto the substrate, the microbolometer's thermal conductance is temporarily
increased roughly three-fold higher than that of the normal state and thermal damage to the bolometer material can be
effectively prevented. The increase of thermal conductance can be controlled by changing the size of the bimorph leg.