Excess Heat Capacity in Mo/Au Transition Edge Sensor Bolometric Detectors.

Excess heat capacity in a bolometric detector has the consequence of increasing or leading to multiple device time constants. The Mo/Au bilayer transition edge sensor (TES) bolometric detectors initially fabricated for the high resolution mid-infrared spectrometer (HIRMES) exhibited two response thermalization scales, one of which is a few times longer than estimates based upon the properties of the bulk materials employed in the design. The relative contribution of this settling time to the overall time response of the detectors is roughly proportional to the pixel area, which ranges between ~0.3 and 2.6 mm2. Use of laser ablation to remove sections of the silicon membranes comprising the pixels results in a detector response with a smaller contribution from the secondary time constant. Additional information about the nature of this excess heat capacity is gleaned from glancing incidence x-ray diffraction, which reveals the presence of molybdenum silicides near the silicon surface which is a consequence of the bi-layer deposition. Quantitative analysis of the concentration of excess molybdenum, estimated with secondary ion mass spectroscopy, is commensurate to the additional heat capacity needed to explain the anomalous time response of the detectors.

Microstructure technology for fabrication of metal-mesh grids.

Motivated by the need for highly efficient far-IR Fabry-Perot étalons for airborne and space astronomy, we have developed a high-yield photolithographic technique for producing low-loss metal-mesh reflectors. We describe the production technique and report on the mesh flatness and uniformity. Optical measurements of meshes produced by this technique show that absorptivity of less than 1% with reflectivity of more than 98% was achieved at the longest wavelengths measured, which proved them to be significantly more efficient than commercially available meshes. This process can achieve wire widths that are less than the mesh thicknesses (typically 3 µm), which extends their applicability to wavelengths as short as ~ 20 µm without sacrificing mechanical strength for airborne and space-flight applications.