Device Level Vacuum Packaged Microbolometers On Flexible Substrates
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Micromachined microbolometers on flexible substrate have been fabricated and characterized. Liquid polyimide PI5878G made by HD Microsystems has been used to form the flexible substrate. Semiconducting Yttrium-Barium-Copper-Oxide (commonly referred to as YBCO) is the temperature sensitive material. These detectors are supported by thin micromachined layers of silicon nitride on flexible polyimide PI5878G. The devices were characterized for temperature dependent resistance (R(T)), the temperature coefficient of resistance (TCR, ), responsivity , detectivity (D*) and thermal conductance (Gth). A typical device had a resistance of 3.76 MI and a TCR of -2.63 %/K at 301 K. The measured thermal conductance was W/K. The device displayed a voltage responsivity of 9.2x102 V/W. The responsivity improved to 7.4x103 V/W when the same device was measured in vacuum, pointing to good thermal isolation because of the micromachining. The maximum recorded detectivity of the device was 6.6x105 cmHz1/2/W. The effect of substrate heating on the detector response was also investigated and found to be negligible. A new device-level vacuum-packaging scheme has been introduced in this work. Devices were fabricated on a rigid silicon substrate as well as a flexible polyimde substrate, packaged and characterized. A TCR of -3.7 %/K was measured. With a voltage bias of 10.1 V across the bolometer, a responsivity of 61.3 μA/W at an optical modulation frequency of 5 Hz was measured. The corresponding detectivity was 5.2x104 cmHz1/2/W. The device on flexible polyimide substrate had a measured thermal conductance W/K while the device on rigid silicon substrate had a measured thermal conductance W/K, one hundred and eighty days after fabrication. These values compare well with the calculated minimum using an analytic model as well as a numeric FEM model. The low thermal conductance of the devices after a lapse of six months points to an intact vacuum cavity containing functional microbolometers. The development of a tunable infrared spectrometer for near and mid infrared region application has also been presented. A Fabry Perot cavity based design was analyzed using finite element method based simulations for optical and structural feasibility.