Phonon-cooled Hot Electron Bolometric Mixers Research Articles

A terahertz focal plane array using HEB superconducting mixers and MMIC IF amplifiers

We present a focal plane array (FPA) designed for operation at terahertz frequencies. The FPA is based on NbN phonon-cooled hot electron bolometer mixers directly coupled to wide-band microwave monolithic integrated circuit IF amplifiers. The array incorporates all the required dc-bias and IF circuitry in a compact split-block design. We present new experimental results describing the optical coupling efficiency to the array, as well as receiver noise temperature measurements. The measurements were performed at 1.6 THz, showing good agreement with theoretical predictions. This is the first low-noise heterodyne focal plane array to be reported for any frequency above 1 THz.

Low noise NbN superconducting hot electron bolometer mixers at 1.9 and 2.5 THz

NbN phonon-cooled hot electron bolometer mixers (HEBs) have been realized withnegligible contact resistance between the bolometer itself and the contact structure. Usinga combination of in situ cleaning of the NbN film and the use of an additionalsuperconducting interlayer of a 10 nm NbTiN layer between the Au of the contactstructure and the NbN film superior noise temperatures have been obtained aslow as 950 K at 2.5 THz and 750 K at 1.9 THz. Here we address in detail the DCcharacterization of these devices, the interface transparencies between the bolometers andthe contacts and the consequences of these factors on the mixer performance.

Improvement of Phonon Diffusion Efficiency in Phonon-Cooled NbN Hot Electron Bolometer Mixers

We propose a superconducting hot electron bolometer (HEB) mixer with an upper heat sink to improve the phonon diffusion efficiency in phonon cooled HEB mixers. We designed and fabricated NbN HEB mixers, and investigated the cooling effect of the upper heat sink by measuring intermediate frequency (IF) bandwidths of the HEB mixers. The SiO films for the upper dielectric heat sink, ranging in thickness from 9 to 35 µm, were deposited on the top of the NbN strip by high vacuum evaporation. We measured the IF bandwidths of HEB mixers, with and without the SiO heat sink, and observed that the 3-dB IF roll-off frequency increased from 0.4 to 0.7 GHz by using a 35-µm-thick SiO heat sink.

1.6 THz heterodyne receiver for the far infrared space telescope

A low noise heterodyne receiver is being developed for the terahertz range using a phonon-cooled hot-electron bolometric mixer based on 3.5 nm thick superconducting NbN film. In the 1–2 GHz intermediate frequency band the double-sideband receiver noise temperature was 450 K at 0.6 THz, 700 K at 1.6 THz and 1100 K at 2.5 THz. In the 3–8 GHz IF band the lowest receiver noise temperature was 700 K at 0.6 THz, 1500 K at 1.6 THz and 3000 K at 2.5 THz while it increased by a factor of 3 towards 8 GHz.

Noise temperature of an NbN hot-electron bolometric mixer at frequencies from 0.7 THz to 5.2 THz

We report on noise temperature measurements of an NbN phonon-cooled hot-electron bolometric mixer in the terahertz frequency range. The devices were 3 nm thick films with in-plane dimensions 1.7 × 0.2 µm2 and 0.9 × 0.2 µm2 integrated in a complementary logarithmic-spiral antenna. Measurements were performed at seven frequencies ranging from 0.7 THz to 5.2 THz. The measured DSB noise temperatures are 1500 K (0.7 THz), 2200 K (1.4 THz), 2600 K (1.6 THz), 2900 K (2.5 THz), 4000 K (3.1 THz), 5600 K (4.3 THz) and 8800 K (5.2 THz).

Phonon-cooled hot-electron bolometric mixer: overview of recent results

Abstract The paper presents an overview of recent results for NbN phonon-cooled hot electron bolometric (HEB) mixers. The noise temperature of the receivers based on both quasioptical and waveguide versions of HEB mixer has crossed the level of 1 K·GHz−1 at 430 GHz (410 K) and 600–650 GHz (480 K) and is close to this level at 820 GHz (1100 K) and 900 GHz (980 K). The gain bandwidth measured for quasioptical HEB mixer at 620 GHz reached 4 GHz and the noise temperature bandwidth was almost 8 GHz. Local oscillator power requirements are about 1 μW for mixers made by photolithography and are about 100 nW for mixers made by e-beam lithography. The studies in terahertz receivers based on HEB superconducting mixers now present a dynamic, rapidly developing field.

New results for NbN phonon-cooled hot electron bolometric mixers above 1 THz

NbN Hot Electron Bolometric (HEB) mixers have produced promising results in terms of DSB receiver noise temperature (2800 K at 1.56 THz). The LO source for these mixers is a gas laser pumped by a CO/sub 2/ laser and the device is quasi-optically coupled through an extended hemispherical lens and a self-complementary log-periodic toothed antenna. NbN HEBs do not require submicron dimensions, can be operated comfortably at 4.2 K or higher, and require LO power of about 100-500 nW. IF noise bandwidths of 5 GHz or greater have been demonstrated. The DC bias point is also not affected by thermal radiation at 300 K. Receiver noise temperatures below 1 THz are typically 450-600 K and are expected to gradually approach these levels above 1 THz as well. NbN HEB mixers thus are rapidly approaching the type of performance required of a rugged practical receiver for astronomy and remote sensing in the THz region.

Investigation of NbN phonon-cooled HEB mixers at 2.5 THz

The development of superconducting hot electron bolometric (HEB) mixers has been a big step forward in the direction of quantum noise limited mixer performance at THz frequencies. Such mixers are crucial for the upcoming generation of airborne and spaceborne THz heterodyne receivers. In this paper we report on new results on a phonon-cooled NbN HEB mixer using e-beam lithography. The superconducting film is 3 nm thick. The mixer is 0.2 /spl mu/m long and 1.5 /spl mu/m wide and it is integrated in a spiral antenna on a Si substrate. The device is quasi-optically coupled through a Si lens and a dielectric beam combiner to the radiation of an optically pumped FIR ring gas laser cavity. The performance of the mixer at different THz frequencies from 0.69 to 2.55 THz with an emphasis on 2.52 THz is demonstrated. At 2.52 THz minimum DSB noise temperatures of 4200 K have been achieved at an IF of 1.5 GHz and a bandwidth of 40 MHz with the mixer mounted in a cryostat and a 0.8 m long signal path in air.

Noise temperature and local oscillator power requirement of NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies

In this letter, the noise performance of NbN-based phonon-cooled hot electron bolometric quasioptical mixers is investigated in the 0.55–1.1 THz frequency range. The best results of the double-sideband (DSB) noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz, and 1250 K at 1.1 THz. The water vapor in the signal path causes significant contribution to the measured receiver noise temperature around 1.1 THz. The devices are made from 3-nm-thick NbN film on high-resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are typically 0.2×2 μm. The amount of local oscillator power absorbed in the bolometer is less than 100 nW.