Low noise MgB2 hot electron bolometer mixer operated at 5.3 THz and at 20 K

Abstract

We have demonstrated a low noise superconducting MgB 2 hot electron bolometer (HEB) mixer working at the frequency of 5.3 terahertz (THz) with 20 K operation temperature. The bolometer consists of a 7 nm thick MgB 2 submicrometer bridge contacted with a spiral antenna to couple THz radiation through a high resistive Si lens, and it has a superconducting critical temperature of 38 K. By using hot/cold blackbody loads and a Mylar beam splitter all in vacuum and applying a 5.25 THz far-infrared gas laser as a local oscillator, we measured a minimal double sideband receiver noise temperature of 3960 K at the LO power of 9.5 lW. This can be further reduced to 2920 K if a Si lens with an antireflection coating optimized at this frequency and a 3 lm beam splitter are used. The measured intermediate frequency (IF) noise bandwidth is 9.5 GHz. The low noise, wide IF bandwidth mixers, which can be operated in a compact, low dissipation Stirling cooler, are more suitable for space applications than the existing HEB mixers. Furthermore, we likely observed a signature of the double-gap in MgB 2 by comparing current-voltage curves pumped at 5.3 and 1.6 THz.

5.3 THz MgB2 hot electron bolometer mixer operated at 20 K

“…In this conference paper, we summarize the results of an MgB2 HEB mixer operated at 5.3 THz, which is the highest frequency studied so far. The key results and their analysis have been published earlier in [19]. We repeat them here, but update the discussions and add necessary details of the HEB fabrication and test setup.…”

“…At this optimal IV, the required LO power is 9.5 μW. Inset (a) is an artistic impression of the HEB, which has the exactly same layout as the design; Inset (b) shows a comparison of the pumped IV curves with the same LO power at 1.6 THz and 5.3 THz, which are measured at 5 K and 20 K, respectively [19].…”

“…3 Measured receiver output power (left axis) of the MgB2HEB in response to hot/cold loads, together with the polynomial fits (in a solid line) as a function of the current and the resulted receiver noise temperature (right axis) when it is operated with an LO at 5.3 THz and at 20 K, and biased at 2.5 mV. The lowest noise temperature is 3960 K. The inset shows the minimum receiver noise temperature from such measurements for different bias voltages, varying from 1 to 7 mV [19].…”

Heterodyne performance and characteristics of terahertz MgB2 hot electron bolometers

“…32, which was based on an 6 nm thick, HPCVD grown film with a T c of 31 K. Very recently, we have reported a measured T DSB rec of 3960 K at 5.3 THz (the highest frequency so far) with 20 K operating temperature using an ∼7 nm HPVCD grown film with a T c of 38.4 K. This T DSB rec gives a DSB mixer noise temperature (T DSB mix ) of 1470 K, derived from a standard relation between the two performance parameters by subtracting the noise and loss contribution from all the optics and the noise from the IF chain using the measured receiver gain. 34 The improvement in the IF bandwidth of MgB 2 HEBs is striking. For example, 11 GHz in Ref.…”

“…32) is a factor of 1.8 higher than a NbN HEB mixer, 36 while at 5.3 THz, this factor is about 2.5 if MgB 2 is operated at 20 K and becomes a factor of 2.1 when it is operated at 6 K or below. 34 To further improve T DSB rec , one needs to explore the device physics, in particular, electrodynamical processes at THz unique to MgB 2 nature such as the high and the double gap feature.…”