(A) research on vacuum packaging technology and pirani pressure sensor for uncooled infrared sensor

Abstract

In this thesis, vacuum packaging technology for enhancing NETD of microbolometer was studied. Also, pi-rani gauge which can measure the vacuum level under 10mTorr was designed and its theoretical leg thermal conductance was $3.25 times 10^{-7}$ W/K. For sensor packaging, Cu-Sn solder bonding was selected. To analyze the effects of bonding parameters, bonding was executed at various conditions. Cu-evaporated silicon wafer and Sn-evaporated silicon wafer were bonded at 260℃, 10000N for 10min, and diced into 4x3, 4x5, 6x3, 6x5 $cm^{-2}$ sizes for shear test. Measured average shear strength was 9.81MPa which was lower than the requirement of packaging shear strength of 12.3MPa. Average shear strength was increased to 21.29MPa if bonding force was increased to 20000N, so shear strength was linearly dependent on bonding force. And bonding temperature and time were insufficient to increase shear strength. Pirani gauge was fabricated by bulk micromachining and its properties were calculated and measured. First, resistances of Pirani gauge were measured at various pressures by flowing 100uA DC current. Initial resistance of 6.8kΩ was increased to 7.0kΩ at 50mTorr. By using this method, resistances of Pirani gauge were obtained at various pressures so these data can be used for measuring vacuum level inside the package. Measured TCR was $9.19times10^{-4}K^{-1}$ and total thermal conductance was $2.57 times 10^{-6}$ W/K. These proposed packaging method and Pirani gauge are suitable for IR sensor packaging and vacuum measurement.