Design and characterization of a single layer uncooled microbolometer detector pixel

In this thesis, fabrication and characterization of a single layer uncooled microbolometer detector are presented. The single layer structure is developed to use the same material as the active material, the structural layer, and the absorber layer, and it is aimed to reveal a cost-effective solution for microbolometer type thermal detectors by decreasing the fabrication complexity. The design starts with the determination of the single layer as Zinc Oxide (ZnO) which is coated with atomic layer deposition technique. Structural design of a single layer microbolometer detector pixel is performed by optimizing the design parameters with the optical, thermal, and mechanical simulations. The short and long-armed pixels are designed with the pitch values of 25, 35, and 50 µm; the ZnO thickness and the cavity thickness values of the designed pixels are optimized to have an absorption amount higher than 85% in the wavelength range of 8-12 µm. The thermal conductance values of the designed pixels are simulated in the range of 5x10-7 and 7.7x10-6 W/K while their thermal time constant values are simulated between 0.2 and 2.8 ms. A four-step process is designed for the fabrication of the single layer microbolometer detectors. The steps are comprised of deposition and patterning of the mirror layer, the sacrificial layer, and the thermistor layer, and the removal of the sacrificial layer. All the steps are optimized separately and it is required to revise the thickness of the ZnO layer and the cavity thickness at the results of the process optimizations as 25 nm and 2.2 µm, respectively. The detectors are fabricated after the revision of the design. Several tests are performed after the fabrication process of the single layer pixels. The TCR of the thermistor layer is measured as -10.5 %/K at 20 °C and the 1/f noise corner frequency is obtained as 302.5 Hz at 5 µA bias current. The average infrared absorption at 8-12 µm wavelength range is measured between 30 % and 39 %. The results of this study show that it is possible to implement a single layer structure for the microbolometers by using ZnO material as the active, the absorber and the structural layers to simplify the fabrication process. By improving the process steps to use a thicker ZnO layer, the performance of the single layer microbolometer detector pixels will be increased and become suitable for low-cost commercial applications.