Performance of the NbTiN hot electron bolometer mixer with AlN buffer layer at terahertz frequency range

We present recent measurements of receiver noise temperature and intermediate frequency (IF) bandwidth in the frequency range 0.8-1.3 THz for waveguide NbTiN HEB mixers of various dimensions. These devices are fabricated from an NbTiN film deposited on crystalline quartz substrates with AlN buffer layer. The lengths of the mixer elements vary from 0.3 to 0.5 μm and their widths vary from 3 to 10 μm. Critical temperatures are typically at 8.5 K, and the measured normal state resistance of the devices is about 1000 ohms per square. All the device DC parameters demonstrate a high degree of uniformity. A double side band noise temperature at 0.8 THz as low as 550 K has been measured at an IF frequency of 1.8 GHz, with a conversion loss of around 14 dB. At an IF of 3 GHz, the noise temperature increases to 750 K. We have also made extensive measurements of the IF bandwidth as a function of bias voltages and currents. At the optimal low-noise operation point, a 3-dB IF bandwidth of 1.2 GHz is obtained for a wide variety of device dimensions and bath temperature.