Terahertz Detector Development

In Project D3 "Terahertz Detector Development", the KOSMA Superconducting Devices and Mixers Group develops ultra-sensitive and fast superconducting detectors for frequencies from 200 GHz to 30 THz (wavelengths 1.5 mm to 10 µm). Although the main application for our detectors lies in astronomy, we also develop detectors for our in-house laboratory spectroscopy groups. The strength of our group lies in the capability to design, fabricate, test and qualify complete detector units - starting from a blank wafer in the cleanroom and ending with a complete unit with all optical, mechanical and electrical interfaces according to the specs required from the receiver (e.g. for (up)GREAT). Our detectors hence are fully characterized and optimized for operation in a receiver at an observatory under real-life conditions. This generally involves a number of iteration cycles for each component, for which corresponding infrastructure and expertise is available in-house. Understanding the underlying detector physics is indispensible for interpretation of the measurement results.
LFA
1.9 THz HEB mixers
for LFA upGREAT
focal plane array
We run a highly specialised micro-fabrication laboratory for superconductor detectors, we use up-to-date high frequency simulation software (CST Microwave Studio™) for (superconducting) circuit design , we use professional CAD design tools and have easy and direct in-house access to an excellent precision machine shop. We acquired and developed high-precision equipment for assembly of devices in (waveguide) block. Well-equipped measurement labs with local oscillator sources giving adequate coverage of the required submm to THz range, spectrometers and several cryogenic setups for RF and DC measurements are available.
 
An important advantage for our group's work is that part of the users of our detectors are also in our institute. The receiver groups make us aware of additional constraints in an early state of the development, and enable much smoother transition from detector development to receiver application. Additionally input from the astronomers and the laboratory spectroscopy users give us valuable feedback on the operation characteristics of the detectors, which subsequently triggers the development of further improvements and additional functionality. Vice versa the people that develop the detectors (i.e. we) are often also involved in the commissioning of a new instrument that employs our detectors.
500 GHz integrated balanced SIS mixer
500 GHz integrated balanced mixer device
Our present  goals in detector development are:
  • SIS mixers for the CHAI focal plane arrays ( 460 GHz, 800 GHz)
    • balanced & sideband separating SIS mixers up to 900 GHz
    • local oscillator distribution for balanced mixer pixels
    • built-in IF power combining in superconducting technology
    • optimizing device design to allow larger tolerances
    •  
  • Microwave Kinetic Inductance Detectors (MKID) protoype array (800 GHz)
    • optimum coupling to telescope
    • manufacturing optimization
  • 1.4THz mixer with Nb-AlN-NbN  SIS junctions
    • large IF bandwidth at 1.4 THz, verification CCAT-p.
  • Extension of current state-of-the-art performance of HEB mixers

    • HEB mixer at 10.7 THz for observation of H2
    • IF bandwidth enhancement (different substrates, buffer layers)
    • New HEB materials

     

upGREAT 4.7 THz
HEB mixer device           positioned on                        waveguide mixerblock

For ground based observatories (e.g. CCAT-p )  more observing efficiency can be achieved by dedicated application of sideband separating techniques, by wider instantaneous bandwidths, and, most importantly, by developing large focal plane arrays with many pixels. The CCAT-p telescope is extremely suitable for observation with large cameras, for which the MKIDs are one of the best choices. The higher THz frequency development is closely related to the unique capabilites of the CCAT-p telescope at the high site, and  to contribute unique single pixel receivers at astronomical important bands to the versatile GREAT receiver on SOFIA.