1.5 THz heterodyne receiver with waveguide superconducting NbTiN hot electron bolometer mixer

Abstract

In this paper, we present measured results and theoretical modeling of a 1.5 THz waveguide NbTiN HEB mixer, which is fabricated by in situ process. The NbTiN HEB mixer with dimensions of 1 μm in width and 0.15 μm in length is measured to be as low as 570 K in noise temperature (7hν/k) even with a relatively thick NbTiN film (10.8 nm). The intrinsic mixer noise temperature is 300 K after the correction of the losses of quasi-optical and IF amplifier chain. At the same time, we adopt an optimized hot spot model to simulate the DC and RF behaviors of the NbTiN HEB mixer by combining phonon-cooling and diffusion-cooling mechanisms together. The measured and calculated current-voltage curves are in good agreement. The calculated intrinsic mixer noise temperature is 100 K and IF gain bandwidth is 2.7GHz at the optimum bias point. The difference between the measured and simulated mixer noise temperature is factor of 3 times, which is probably due to misalignment of quasi-optical RF coupling system and air loss. The calculated and measured results show the two cooling mechanism work together to lower the noise temperature of the waveguide NbTiN HEB mixers. The details will be presented in this paper.