Intrinsic mixing behavior of superconducting NbTiN hot electron bolometer mixers based on in situ technique

2013 
Abstract In this paper, we present the comparison of measured and simulated results for 0.8 and 1.5 THz waveguide NbTiN HEB mixers fabricated by in situ technique, with a relatively thick NbTiN film (10.8 nm). The dimension of NbTiN HEB mixers are 1–1.5 μm in width and 0.15–0.2 μm in length respectively. The lowest receiver noise temperature is measured to be as low as 410 K and reduced to 210 K after the correction of the losses of quasi-optical path and IF amplifier chain at both 0.8 and 1.5 THz. 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 modeled lowest intrinsic mixer noise temperature are 85 and 100 K at 0.8 and 1.5 THz respectively, which are smaller than the measured results by factor of about 2 times. The IF gain bandwidth are observed to be quite sensitive to the microbridge length, with 2.5 GHz for 0.15-μm long device down to 1.9 GHz for 0.2-μm length. The calculated and measured results show the two cooling mechanism work together to improve the performance of the waveguide NbTiN HEB mixers.
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