Niobium Titanium Nitride Thin Film Coating

materials and coatings
Niobium Titanium Nitride Thin Film Coating (GSC-TOPS-221)
Simultaneously acts as a high pass filter and mid-to-far infrared absorber at cryogenic temperatures
Overview
Impedance matched coatings are used for absorber applications to couple mid-to-far infrared (IR) radiation to an ultrasensitive bolometric detector suspended on an ultrathin dielectric membrane. In order to provide adequate responsivity, the bolometric detector must have a low heat capacity. Furthermore, to achieve an optimal signal-to-noise ratio, spectral filtering of the incident radiation is desirable. Conventional approaches for absorber coatings are susceptible to aging, which hinders the transient optical efficiency of the instrument. Additionally, conventional absorber coatings have a high heat capacity which impact the performance of low-background cryogenic detectors. Conventional absorber coatings also are reactive in the short wavelength limit, which correspondingly reduces their coupling efficiency. Furthermore, some thin film absorber coatings have extremely high intrinsic stress, which can cause the dielectric membranes to break or bend. The Niobium Titanium Nitride Thin Film Coating does not have these disadvantages.

The Technology
The Niobium Titanium Nitride (NbTiN) Thin Film Coating can optically couple light to a bolometric detector, which is suspended on an ultra-thin dielectric membrane. The coating can also filter out low frequency spectral components, which would increase the photon-limited noise of the detector. NbTiN thin film coatings are fabricated on dielectric substrates using a specialized reactive sputtering co-deposition process. Two different sputtering sources are used, in which one source contains a niobium sputtering target and the other contains a titanium sputtering target. The niobium and titanium are deposited in a nitrogen-rich environment. NbTiN coating can be used by depositing it on one side of an ultra-thin silicon membrane and have a well-defined optical impedance requirement for a specific application. NbTiN coating can be deposited on non-silicon membranes as well. The NbTiN coating have low intrinsic stress, which makes it mechanically compatible with integration on ultra-thin dielectric membranes. The coating possesses the optical impedance required for a high optical efficiency absorption. Furthermore, the coating has a very low superconducting transition temperature, which enables it to filter out radiation at certain frequencies. The NbTiN coating is especially useful for ultrasensitive cryogenic bolometric detector applications. The NbTiN coating can be fabricated in a reproducible manner, while simultaneously not complicating the fabrication process of detector architectures.
The powerful primary mirrors of the James Webb Space Telescope will be able to detect the light from distant galaxies. The manufacturer of those mirrors, Ball Aerospace & Technologies Corp. of Boulder, Colo., recently celebrated their successful efforts as mirror segments were packed up in special shipping canisters (cans) for shipping to NASA. The Webb telescope has 21 mirrors, with 18 primary mirror segments working together as one large 21.3-foot (6.5-meter) primary mirror. The mirror segments are made of beryllium, which was selected for its stiffness, light weight and stability at cryogenic temperatures. Bare beryllium is not very reflective of near-infrared light, so each mirror is coated with about 0.12 ounce of gold.
Benefits
  • Simple fabrication
  • Low heat capacity
  • Not susceptible to aging
  • Non-reactive in the short wavelength limit

Applications
  • Terahertz medical imaging
  • Terahertz communications
Technology Details

materials and coatings
GSC-TOPS-221
GSC-17851-1
10458853
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