A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si3N4/SiO2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. The gain bandwidth of the HEB mixers on Si3N4/SiO2 membranes was found to be 0.7÷0.9 GHz, which is much smaller than for similar devices on silicon. Application of buffer layers and use of alternative types of membranes (e.g. silicon-on-insulator) is under investigation.
In this paper recent developments of Hot Electron Bolometric receivers performed at Chalmers are summarized. This comprises progress on the mixers for HIFI and membrane HEB. All devices are modelled using Hot Spot model taking Andreev reflection at the interface between the normal conductor and the superconductor into
We present in this paper the front-end design and the results of RF simulations, carried out with Microwave Studio (CST) and HFSS for SHAHIRA (Submillimeter Heterodyne Array for High-speed Radio Astronomy), a 4x4 heterodyne array at 2.5 THz and 4.7 THz. One can then observe 16 spatial positions at 2 frequencies. The design has been chosen to be quasi-optic, because of its simplicity, novelty and multi-pixels applicability. Pixels are made of Niobium Nitride HEB mixers with double-slot antennas, processed on 1 μm thick stress-less Si3N4/SiO2 membrane. The use of the membrane shows numerous advantages: for instance the use of the mixers at higher RF frequencies, a better power coupling efficiency or a solution for avoiding dielectric modes, losses and reflections. This work is supported by ESA and is a collaboration between LERMA, CHALMERS and LAAS. The Camera is expected to find applications, for SOFIA or CIDRE.
We report in this paper a new concept for 2.7 THz superconducting Niobium nitride (NbN) Hot-Electron Bolometer mixer (HEB). The membrane process was developped for space telecommnunication applications a few years ago and the HEB mixer concept is now considered as the best choice for low-noise submillimeter-wave frequency heterodyne receivers. The idea is then to join these two technologies. The novel fabrication scheme is to fabricate a NbN HEB mixer on a 1 μm thick stress-less Si3N4/SiO2 membrane. This seems to present numerous improvements concerning : use at higher RF frequencies, power coupling efficiency, HEB mixer sensitivity, noise temperature, and space applications. This work is to be continued within the framework of an ESA TRP project, a 2.7 THz heterodyne camera with numerous applications including a SOFIA airborne receiver. This paper presents the whole fabrication process, the validation tests and preliminary results. Membrane-based HEB mixer theory is currently being investigated and further tests such as heterodyne and Fourier transform spectrometry measurement are planed shortly.