| A bolometer for infrared detection and imaging, operating at room temperature, is presented. The detector consists of a metal thin film deposited over a suspended SiO2 membrane using thermal evaporation. The suspended membrane increases responsitivity by minimizing thermal conductance and is fabricated by employing an isotropic etch to remove the underlying Si substrate from the front-side of the wafer. The membrane size is 100 mum x 12 mum x 0.8 mum. Extensive characterization was performed including measurements of film resistivity and temperature coefficient of resistance as a function of thickness. As well, various metals were explored including Ni, Bi, Au and Cr and Hall measurements were carried out on the Bi thin films since these films show the most preferable characteristics. For optimal devices, the responsitivity is close to 10 V/W and the time response is 130 mus.;To specifically demonstrate the effect of the SiO2 suspended membrane on thermal conductance, bolometers fabricated with conventional bulk substrates are also presented. These devices have a thermal conductance three orders of magnitude larger than the devices made using the suspended membrane. Moreover, the responsitivity is 10-5 V/W.;A novel micromachining procedure is presented for the fabrication of suspended single crystal silicon membranes on (111) Si. The thickness of the membrane and the vertical separation from the substrate are both easily controlled through the process. Typical values for both parameters lie in the range of 0.1 to 20 microns. Such a structure has many applications including the mechanical support for high-Tc bolometers. |
