Development of low-noise high value chromium silicide resistors for cryogenic detector applications Original Research Article

Extremely high sensitivity detectors, such as silicon bolometers are required in many NASA missions for detection of photons from the X-ray to the far infrared regions. Typically, these detectors are cooled to well below the liquid helium (LHe) temperature of 4.2 K to achieve the maximum detection performance. As photodetectors, they are generally operated with a load resistor and a pre-set bias voltage, which is coupled to the input gate of a source-follower field effect transistor (FET) circuit. It is imperative that the detector system signal-to-noise performance be limited by the noise of the detector and not by the noise of the external components. The load resistor value is selected to optimize the detector performance. These two criteria tend to be contradictory in that these detectors require load resistors in the hundreds of megaohms, which leads to a higher Johnson noise. Additionally, the physical size of the resistor must be small for device integration as required by such missions as the NASA High Resolution Airborne Wide-Band Camera instrument and the Submillimeter High-Angular Resolution Camera for the Caltech Submillimeter Observatory, both of which employ 384 detectors and resistors. We have designed, fabricated and characterized thin film resistors using a CrSi/TiW/Al metal system on optical quality quartz substrates. The resistor values range from 75 MΩ to over 650 MΩ and are Johnson noise limited to below LHe temperatures. The resistor film is sputtered with a sheet resistance ranging from 300 to 1600 Ω/□ and the processing sequence developed for these devices allows for chemically fine-tuning the sheet resistance in situ. The wafer fabrication process was of sufficiently high yield (>80%) providing clusters of good resistors for integrated multiple detector channels, a very important feature in the assembly of these two instruments.