Development of a germanium silicon oxide CMOS compatible micromachined infrared detector for thermal imaging applications

The goal of this thesis is the improvement, and performance optimization of a CMOS compatible micromachined bridge-type microbolometer for thermal imaging applications through the use of a new high thermal sensitivity material and optimizing design parameters.; In this work, thin films of GexSi1-xO y were prepared by reactive magnetron sputtering using simultaneous sputtering of silicon and germanium targets in an environment of oxygen and argon. Silicon and oxygen content were varied from 0--30 at% separately and the effect of the addition of each element on electrical and optical properties of amorphous germanium was studied. The electrical and optical behavior of the compound with varying elemental composition is explained based on the oxidation behavior of the Si and Ge. Increasing the silicon content was found to inhibit the formation of germanium-oxygen bonds. Values of temperature coefficient of resistance as high as -5% K-1 were obtained at moderate resistivity values less than 5 x 104 O-cm. These characteristics could be used to enhance the performance of CMOS micromachined uncooled bolometers. The composition control enabled by co-sputtering components allows resistivity and activation energy to be tailored to suit different design specifications.; This semiconductor material was used in the fabrication of a surface micromachined micro bridge type bolometer, which is compatible with any standard CMOS process. The bolometer has the advantage of self-absorbing infrared radiation, requiring no additional absorber layer, and is self supported by its contact metal arms with no additional support structure. The device uses a vertical current flow design and both sandwich and sandwich-gap configurations suitable for a high resistivity a-GexSi1-xOy sensing layer are illustrated. Optimum polyimide sacrificial layer patterning for subsequent deposition of layers is described, and optimum metal thickness for the required sheet resistance is studied. High uniformity of the deposited semiconductor layer is obtained through use of a recessed contact structure; optimum conditions for releasing the structure are described. Three self-supporting suspension mechanisms were investigated for production. While satisfying results could not be achieved for high fill factor side suspension mechanisms, very good results were achieved for lower fill factor central and corner suspension mechanisms. Bolometers having up to 50 microns arm length could be released for both mechanisms, achieving thermal isolation as high as 1.36 x 10 -7 W/K. Noise performance of the produced bolometers was investigated, 1/f noise factor for the used GexSi1-xOy compound was measured, and found to be 2.9 x 10-11 . High thermal isolation along with high TCR enabled a high performance bolometer. Very good responsivity and detectivity of 1.05 x 10 5 V/W, 6.7 x 108 Jones respectively were measured with noise equivalent temperature difference (NETD) of 190mk and thermal response time of 13ms, suitable for TV frame rate thermal imaging applications.