We present the design of a cryogenic system for testing different technologies of millimeter wavelength detectors. The proposed design is developed at the Astronomical Instrumentation Laboratory for Millimeter Wavelength at the National Institute of Astrophysics, Optics and Electronics, in México. The cryogenic system is integrated by a closed cycle pulse tube cooler with a 4 Kelvin 12 inches cold plate and a He-4/He-3 fridge and would be able to characterize KIDs (Kinetic Inductor Detectors), TES (Transition Edge Sensors) or semiconductor bolometers using a thermal link to a 250 mK stage. Readout electronics will be installed at the 4 Kelvin cold plate along with connectors and cables for the thermometry. In this paper we present a preliminary 3D model design which its main goal is to use efficiently the limited space in the cryostat with emphasis on the interchangeability for installing each time any of the three different detector technologies in the same cold plate; results for the thermal calculations and finite-element modeling are also shown. The system would allow, with some minor changes, to replace the He-4/He-3 fridge by a dilution fridge in order to reach temperatures about 100 mK to have more flexibility in the detector testing. The importance of the cryogenic test bench relies in the need for an easier and quicker characterization of detectors arrays as part of the research for the development of instruments for millimeter telescopes.
We present the characterization of a boron doped hydrogenated amorphous silicon (a-Si:H) thermosensor bolometer
array for far infrared detection. The array was fabricated over a silicon wafer on a 0.4 μm silicon-nitride (Si3N4) layer.
Wet bulk micromachining was used to create pixels of suspended nitride film by removing the silicon underneath. On
this film, a boron doped a-Si:H layer was deposited using a low frequency PECVD system at 540 K. Conventional
lithography was used to define the bolometers on the nitride windows, and the 5 × 5 microbolometer array was fabricated
and characterized at 77 K. A 1.17 x 10-2 mA/W responsivity, with a temperature coefficient of resistance (TCR) of
4.25%, were obtained.