The article is concerned with the experimental evidence that proves technical feasibility of the hybrid planar integration (HPI) scheme that has been proposed to construct superconductor-insulator-superconductor (SIS) mixer focal plane arrays of unprecedented compactness. The scheme is characterized by the adoption of silicon membrane-based waveguide probes, which allows superconducting monolithic microwave integrated circuits to couple signal, and local oscillator (LO) from (computer numerical control)-machined waveguides through multiple paths. A 2 x 2 dual-polarization balanced SIS mixer array has been implemented with this scheme, and assessed in 125 - 163 GHz RF band. This compact array has demonstrated uniform LO distribution, and low crosstalk between pixels. The RF performance of component pixels has been confirmed to be little affected by the high-degree integration. The potential implementation of the HPI scheme at THz frequencies is also discussed.
The article is concerned with the experimental evidence that proves technical feasibility of the hybrid planar integration (HPI) scheme that has been proposed to construct superconductor-insulator-superconductor (SIS) mixer focal plane arrays of unprecedented compactness. The scheme is characterized by the adoption of silicon membrane-based waveguide probes, which allows superconducting monolithic microwave integrated circuits to couple signal, and local oscillator (LO) from (computer numerical control)-machined waveguides through multiple paths. A 2 x 2 dual-polarization balanced SIS mixer array has been implemented with this scheme, and assessed in 125 - 163 GHz RF band. This compact array has demonstrated uniform LO distribution, and low crosstalk between pixels. The RF performance of component pixels has been confirmed to be little affected by the high-degree integration. The potential implementation of the HPI scheme at THz frequencies is also discussed.
Large-format heterodyne focal plane arrays require highly integrated receiver architectures while maintaining low noise and sufficient sideband rejection, which remains challenging for superconducting SIS mixers at millimeter wavelengths. In this work, we demonstrate, for the first time, a monolithic dual-polarization sideband-separating superconductor-insulator-superconductor (SIS) mixer operating at 2 mm wavelengths (125-163 GHz) on a silicon-on-insulator substrate. The integrated SIS mixer achieves a sideband rejection ratio exceeding 10 dB over the 4-8 GHz intermediate-frequency (IF) band across most of the radio-frequency (RF) range, with a minimum single-sideband (SSB) receiver noise temperature as low as approximately 60 K. As a key building block of the hybrid planar integration (HPI) architecture, this result verifies the feasibility of highly integrated large-format heterodyne focal plane arrays, providing a practical path toward substantially expanding the field of view of millimeter and submillimeter-wave radio telescopes.
This thesis work covers the development of integrated superconducting balanced mixers for heterodyne (resolution> 10^7) THz focal plane arrays. The aim was to develop on chip integrated balanced superconductor-insulator-superconductor (SIS) mixers at 800-1100 GHz and in addition at the Intermediate Frequency (IF) 4-12 GHz integrated \n180° IF hybrids both for the CHAI (CCAT Heterodyne Array Instrument) receiver for the Cerro Chajnantor Atacama Telescope (CCAT) observatory. A planar 180º hybrid ring \ncoupler, two separate slotline antennas, two separate slotline to CPW transitions to employ for the 800-1100 GHz balanced SIS mixer, based on NbTiN circuitry, were designed and all were integrated on one 6 μm silicon substrate. \nAt the IF side of the integrated balanced mixers, two different configurations of superconducting \nintegrated 180º IF hybrids were designed to combine the two generated IF outputs at either Σ or Δ port depending on the choice of the input port of the hybrid. These 4-12 GHz IF hybrid coupler designs were based on planar lumped elements to miniaturize the size to about 0.5×2.2 μm^2. The designs were simulated for 500 μm and 9 μm silicon substrates. The latter is studied in order to integrate it at a later \nstage with the RF part of the mixer on one substrate. The lithography mask and subsequently the micro-fabrication of the IF hybrids were made. The measurement of the Nb based IF hybrid on a 500 μm silicon with Vector Network Analyzer (VNA) in liquid helium is reported. The measured results are analyzed and compared to the IF hybrid with the implemented superconducting Nb in the simulation. \n \nThese developments and designs will be available and applicable for future receivers of the CCAT-prime observatory. Because the original envisioned CCAT-observatory project was discontinued due to the lack of funding, it was decided that my 800-1100 GHz designs would not be further developed into working mixers for the time being and that other projects would get priority. \n \nMy work continued with the the development of integrated 1.9 THz balanced Hot Electron Bolometer (HEB) mixers. This development is relevant for 1.9 THz focal plane array receivers for the airborne Stratospheric Observatory for the Far Infrared (SOFIA), for which the mixers are developed in our group. The LO power consumption of the array presently limits its usable RF bandwidth. This power consumption could be reduced by a factor of 5 by using integrated balanced mixers. The mixers are based on superconducting NbN HEBs and Au is applied as normal metal to wire the mixers. The development contained design, micro-nanofabrication, DC and cryogenic high frequency measurements. All designed planar elements consisted of an 1 octave broadband 180º RF hybrid-ring coupler, two slotline tapered antennas, two slotline to \nCPW transitions, two or four 120 Ω HEB bridges, two low pass filters (LPFs) and two DC/IF blocking capacitors integrated on one 3 μm silicon substrate and simulated using CST suite. A further integrated 1.9 THz HEB mixer was designed to support the two separate IF outputs at one side of a 3 μm silicon substrate with employing a CPW-CPW crossover. \n \nThe micro-nanofabrication of the 1.9 THz balanced mixers was done in house using E-beam and photo-lithography techniques. Almost all DC measured devices contained HEB bridges that were sufficiently similar in normal state resistance and transition temperature. The average resistance of the devices, in the one available wafer for measurements, was about 17% too low. The transition temperature of the devices was around 7.9 K, in comparison to 8.5 K for our state of the art single pixel mixers. The two machined 1.9 THz balanced waveguide blocks for testing of the devices were machined in the institute's in house workshop. I have tested the transmission of the blocks, and thereby the workmanship, with a THz time Domain Spectrometer, showed about 2.4 dB of loss per mm waveguide length at room temperature, for a split block waveguide made of the oxygen free copper tellurium alloy (CuTe). \n \nThe cryogenic RF measurements showed a very similar LO-power coupling to both mixers in the balanced device, from both input ports of the mixer. By using an in house built Quantum Cascade Laser (QCL) LO as a local oscillator and a severely attenuated Virginia Diode multiplier chain (VDI) LO as a signal source I have shown proper balanced mixer behavior, thereby validating the design. Signal suppression up to 38 dB was shown by inverting the bias voltages on one of the mixers in the balanced device, which added a 180º phase change to the IF of one of the mixers.
We present a conceptual framework of planar SIS mixer array receivers and the studies on the required techniques. This concept features membrane-based on-chip waveguide probes and a quasi-two-dimensional local-oscillator distribution waveguide network. This concept allows sophisticated functions, such as dual-polarization, balanced mixing and sideband separation, easily implemented with the SIS mixer array in the same planar circuit. We have developed a single-pixel prototype receiver by implementing the concept in the design. Initial measurement results show good evidences that support the feasibility of the concept.
We report the design of a 230 GHz dual-polarization (2-pol) balanced Superconductor-Insulator-Superconductor (SIS) receiver that can be easily extended for large array applications. We achieve this by integrating all of the required radio frequency (RF) and local oscillator (LO) components on-chip using planar superconducting circuit technology, therefore simplifying the architecture of the receiver block substantially. One major feature of our design is the planar LO injection scheme, which couples the LO with a single on-chip antenna and distributes the LO power via a series of microstrip couplers to the balanced mixers of each polarization of each pixel. In this paper, we describe in detail the design and layout of the individual planar circuit components of our receiver, as well as how they are integrated to form a full receiver. We then conclude the paper with the design of a 2-pixel array demonstrator, illustrating how the balanced SIS mixer and the LO distribution network can be extended to form an even larger array.
We present a conceptual framework of planar SIS mixer array receivers and the studies on the required techniques. This concept features membrane-based on-chip waveguide probes and a quasi-two-dimensional local-oscillator distribution waveguide network. This concept allows sophisticated functions, such as dual-polarization, balanced mixing and sideband separation, easily implemented with the SIS mixer array in the same planar circuit. We have developed a single-pixel prototype receiver by implementing the concept in the design. Initial measurement results show good evidences that support the feasibility of the concept.
The Atacama Pathfinder EXperiment (APEX) is a 12 m antenna operating at the Atacama Desert on the Chilean Andes at about 5000 m altitude. APEX would be equipped with a suit of single-pixel heterodyne receivers covering 211 - 1500 GHz frequency range. We present here a design of a sideband-separating superconductor-insulator-superconductor (SIS) mixer for the APEX, receiver Band 3, operating in 385 - 500 GHz band. The receiver uses quadrature scheme with the RF signal passing via a 90-degree waveguide 3 dB hybrid and the LO is divided by a waveguide E-plane Y-junction. The outputs of the waveguide hybrid are coupled to the mixer SIS junctions through an E-probe with integrated bias-T. For the LO coupler, conventional branch waveguide couplers are difficult to manufacture at this high frequency with required accuracy as the branch waveguides become extremely narrow. In order to solve this problem, we propose an on-chip LO injection, where the LO coupler is integrated onto the mixer chip and fabricated together with the SIS junction and the tuning circuitry. The on-chip LO coupler is made of superconducting lines, which gives almost a lossless solution and provides fabrication accuracy better than 0.5 μm by using optical lithography only. Furthermore, the mixer design includes a novel component, an ellipse termination for the idle LO port, made of thin-film resistive material with sheet resistance equal to the transmission line characteristic impedance, which gives very broadband performance using extremely compact area.