Device Level Vacuum Packaged Microbolometers On Flexible Substrates

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Title: Device Level Vacuum Packaged Microbolometers On Flexible Substrates
Author: Mahmood, Aamer
Abstract: 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 .
URI: http : / /hdl .handle .net /10106 /7
Date: 2007-08-23


Device Level Vacuum Packaged Microbolometers On Flexible Substrates. Available electronically from http : / /hdl .handle .net /10106 /7 .

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