3w Thermal Conductivity Measurements of Thin Film Dielectrics on Silicon for use in Cantilever-based IR Imaging

For certain MEMS applications the thermal conductivity (k) of the dielectrics used in fabrication can be an important design parameter. One such application is uncooled infrared (IR) imaging, where absorbed radiation causes a measurable temperature change on a focal plane array of pixels [1, 2, 3]. The performance of the imaging array is critically dependent on the ability to control the time constant for thermal response, which in turn requires precise knowledge of k for each constituent material of the pixel structure. In particular, the pixel's thermal isolation must have a time constant that is compatible with the desired frame rate of the camera; the time constant being a ratio of the specific heat of the structure and the thermal conductance. Special attention must also be paid to the stress of the thin films and their etch resistance compared to the sacrificial materials. For uncooled arrays based on micro-cantilevers [4, 5], the dielectric can also act as the low thermal expansion material in the bimorph stack and the stress control becomes even more important. In this work, we investigate some common dielectrics deposited on silicon wafer substrates that might be candidates for micro-cantilever IR imagers.