Measurement of effective absorptance on microbolometers

Microbolometers fabricated by micromachining technology are important for uncooled thermal infrared sensing. Sensors with microstructure can improve their thermal behavior effectively, namely, faster responses and better sensitivities. It is essential to a microbolometer to have their device parameters, thermal and electrical, being extracted, in order to evaluate the processes producing the devices and to facilitate an electro-thermal SPICE model for integrated simulation. Among these parameters, the TCR and resistance can be gotten by a temperature-controlled oven. The thermal conductance and capacitance can be obtained accurately by the AC method which was published in IMTC'97. However, the absorptance of sensors still have no good and reliable method to be extracted. One of the several difficulties in measuring the absorptance is that the absorptance of V-groove type sensor is not equivalent to the surface layer of the sensor. The reflection from the V-groove should be considered to the effective absorptance. The paper demonstrates a pure electrical method without optical alignment and accurate temperature control to measure the effective absorptance fast and accurately. The fact is that the microbolometer decreases the solid thermal conductance because of microstructure, and will be dominated by radiative heat loss under the vacuum surrounding and a high sensor temperature. The measuring results of the effective absorptance are about 1.2 and consistent under the different vacuum condition, 0.1, 0.01, and 0.001 torr. The electrical method does not increase the reliability only, but also simplification of apparatuses significantly.