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