Cold-Electron Bolometers fabricated with Direct Write Technology for Microwave Receiver systems
Doctoral thesis, 2017
This thesis concerns the development of microwave detector technology for cosmology instruments and THz imaging, including fabrication of SIN tunnel junctions for thermometry and bolometric detectors, and also phase switch circuits as a part of integrated microwave receiver systems. Cold-Electron Bolometers (CEB) based on Superconductor-Insulator-Normal metal (SIN) tunnel junctions have been developed for employment in sub-millimeter astronomical receivers. While used as direct detectors, their operation principle is based on hot-electron effect in nanoabsorbers and the dependence of SIN junction characteristics on temperature. In this thesis, the technology development for fabricating bolometric detectors based on these principles is presented, as well as CEB devices fabricated with the new technology and operating at 97 - 350 GHz. The successful operation of CEB devices is reported here, including different advanced implementations of bolometers for effective detection of microwave electromagnetic signals. New fabrication technologies developed for manufacturing CEB, on-chip thermometers, THz detectors and Phase Switch devices are presented. The necessity of this development work was determined by the demand of a robust and straightforward process for fabricating CEB devices with SIN tunnel junctions of large area, at high yield and good reproducibility. Advanced procedures developed for fabricating CEB devices include e.g. Direct-Write Trilayer Technology and Ti-based technology that enable fabricating devices of any geometry, with no limitations related to the layout. This is suitable for integrating the devices in planar antennas, such as log-periodic and double-dipole antennas or finline-shaped slotlines. Properly operating CEB devices are demonstrated, characterized by measuring their DC characteristics and RF response at 280-315 mK. RF testing was performed using hot-cold method and using a black-body source heated by external current, with the estimated NEP down to about ~3∙10^-17 W/Hz^1/2 reported. Fabricating and testing these devices allows demonstrating the full functionality of the CEB detector fabricated with new technology and integrated in various planar circuits. All devices presented here were fabricated by the author at Chalmers MC2.