Effect of the Critical and Operational Temperatures on the Sensitivity of HEB Mixers

Abstract

We present a study of the noise and the gain of MgB2 hot-electron bolometer mixers with different critical temperatures (Tc) and at various operation temperatures. At a Local Oscillator (LO) frequency of 1.63THz the minimum input receiver noise temperature (Tr) was 700K with a gain of-18dB for a device with a Tc of 8.5K. For a device with a Tc of 22.5K the corresponding values were 1700K and-19dB. For the latter device the Tr was 2150K at a bath temperature of 12K, which is not achievable with Nb-compound based HEB mixers. We present and compare different methods for measurements of the HEB mixer gain and the output noise.

Low noise terahertz MgB2 hot-electron bolometer mixers with an 11 GHz bandwidth

“…The T out of 210 K is higher than the previously reported 80 K for devices made of MgB 2 film with a T c of 22 K. 13 We explain this fact by the higher T c (30 K vs. 22 K) used in the current work (see discussion above). The increased mixer gain from À15 dB (from Ref.…”

“…The increased mixer gain from À15 dB (from Ref. 13) to À9 dB (this work) can be attributed to the same increase of the T c (leading to a higher LO power, and hence to the mixer gain 27 ), as well as to the reduced antenna/HEB contact resistance achieved with in-situ cleaning. High mixer gain and high output noise is a preferred combination for heterodyne receivers, because it reduces the effect of the LNA noise in the IF readout.…”

“…10 Although a Double Sideband (DSB) receiver noise temperature, T r of 700 K has been demonstrated at both 0.6 THz (Ref. 12) and 1.6 THz, 13 these devices were made of MgB 2 films with a T c of 9 K, and the noise bandwidth (NBW) (the IF where T r rises Â2 of its value at zero IF) did not exceed 3.5 GHz. Using 20 nm MgB 2 films with a T c of 22 K, T r of 1700 K was achieved with a NBW of 5 GHz.…”

“…Using 20 nm MgB 2 films with a T c of 22 K, T r of 1700 K was achieved with a NBW of 5 GHz. 13 Reduction of the film thickness below 20 nm led to a drop of T c . The next step forward was made with MgB 2 thin films deposited by Hybrid Physical Chemical Vapor Deposition (HPCVD) and 10-20 nm thick films with a T c ¼ 33 K-37 K have been obtained.…”

“…In order to acquire intrinsic mixer parameters, a Ufactor technique with a HEB in normal state (as a reference state) can be utilized. 13 With the HEB at 5 K and at minimum noise temperature point, the U-factor is $8.5 dB (Figure 3(b), curves 3 and 7), which gives a T out of $210 K. An output noise of 40 K-50 K has been reported for NbN HEB mixers with a T c of 9 K. 26 At optimal bias point, T out for HEB mixers is expected to be affected by two contributions: the temperature fluctuations noise (/T c 2 ), and the Johnson noise (/T c ). Therefore, the obtained output noise temperature for MgB 2 mixers falls into the expected range.…”