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Can NbN films on 3C-SiC/Si change the IF bandwidth of hot electron bolometer mixers?

J. R. Gao, Merlijn Hajenius, Frans D. Tichelaar, B. Voronov, E. Grishina, T. M. Klapwijk, Gregory N Gol'tsman, Christian A. Zorman

Published May 1, 2006• 5 citations
OpenAlex

Abstract

We realized ultra thin NbN films sputtered grown on a 3C-SiC/Si substrate. The film with a thickness of 3.5-4.5 nm shows a 1', of 11.8 K, which is the highest I`, observed among ultra thin NbN films on different substrates. The high-resolution transmission electron microscopy (HRTEM) studies show that the film has a monocrystalline structure, confirming the epitaxial growth on the 3C-SiC. Based on a two-temperature model and input parameters from standard NbN films on Si, simulations predict that the new film can increase the IF bandwidth of a HEB mixer by about a factor of 2 in comparison to the standard films. In addition, we find standard NbN films on Si with a T c of 9.4 K have a thickness of around 5.5 nm, being thicker than expected (3.5 nm).

Related papers

Ultra-thin film NbN depositions for HEB heterodyne mixer on Si-substrates

Sascha Krause, Vincent Desmaris, Alexey Pavolotsky +3 more

The key of improving hot-electron bolometer (HEB) mixer performance lies inevitably in the quality of ultra-thin NbN films itself. This work presents a thorough investigation of crucial process parameters of NbN films deposited by means of reactive DC-sputtering on Si-substrates at elevated temperatures up to 750°C.The polycrystalline NbN films with thickness of 4 to 10nm were characterized by DC resistivity measurements, ellipsometry and high resolution transmission electron microscopy (HRTEM) in order to confirm thickness and film structure. Since the macroscopic properties such as critical temperature, thickness as well as the transition width to the superconducting state are directly linked to HEB mixer noise temperature and IF bandwidth, a set of experiments were conducted to enhance aforementioned properties. We considered deposition temperature, RF biasing, nitrogen and argon partial and total pressure during deposition as major process variable parameters. Careful optimization of the deposition conditions allowed setting up a process resulting in high-quality NbN ultra-thin films with thickness of 5.5nm exhibiting Tc of 10.5K. Moreover, the transition width could be kept as low as 1.4K. The produced films were stored at ambient conditions and re-characterized over a period of 4 month without measurable degradation.

•Jan 1, 2013•0 citations

Study of IF bandwidth of NbN hot electron bolometers on GaN buffer layer using a direct measurement method

Sascha Krause, Vladislav Mityashkin, Sergey V. Antipov +5 more

In this paper, we present a reliable measurement method to study the influence of the GaN buffer layer on phonon-escape time in comparison with commonly used Si substrates and, in consequence, on the IF bandwidth of HEBs. One of the key aspects is to operate the HEB mixer at elevated bath temperatures close to the critical temperature of the NbN ultra-thin film, where contributions from electron-phonon processes and self-heating effects are relatively small, therefore IF roll-off will be governed by the phonon-escape.Two independent experiments were performed at GARD and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. The entire IF chain was characterized by S-parameter measurements. We compared the measurement results of epitaxial NbN grown onto GaN buffer-layer with Tc of 12.5 K (4.5 nm) with high quality polycrystalline NbN films on Si substrate with Tc of 10.5 K (5 nm) and observed a strong indication of an enhancement of phonon escape to the substrate by a factor of two for the NbN/GaN material combination.

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Fabrication and IF bandwidth measurements of NbN hot‐electron bolometers

Shigehito Miki, Yoshinori Uzawa, Akira Kawakami +1 more

Abstract As part of an effort to develop heterodyne rf receivers operating in the terahertz band, we have fabricated hot‐electron bolometers (HEB) using NbN thin films, and investigated their intermediate frequency (IF) bandwidths. The NbN thin films we studied were grown on single‐crystal MgO substrates by dc reactive sputtering. Our 2.8‐nm‐thick films exhibited superior superconducting properties, including transition temperatures TC of 9.7 K and 20 K resistivities ρ20 of 185 µΩ·cm. Using electron beam diffraction, high‐resolution TEM images, and other techniques to study the crystallinity of these films, we determined that the NbN grows epitaxially on the MgO substrate as single‐crystal material. The HEB elements we made consisted of a NbN microstrip, a Au electrode section, and an Al antenna section. In the course of studying the IF bandwidths of these devices in the millimeter‐wave range, we found one device with an IF bandwidth of 2.5 GHz, the highest of any device we made. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(7): 77–83, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecjb.1111

Electronics and Communications in Japan (Part II Electronics)•Jun 18, 2002•16 citations

GAIN BANDWIDTH OF PHONON-COOLED HEB MIXER MADE OF NBN THIN FILM WITH MgO BUFFER LAYER ON Si.

Yu. B. Vachtomin, Matvey I. Finkel, Sergey V. Antipov +5 more

We present recently obtained values for gain bandwidth of NbN HEB mixers for different substrates and film thicknesses and for MgO buffer layer on Si at LO frequency of 0.85-1 THz. The maximal bandwidth, 5.2 GHz, was achieved for the device on MgO buffer layer on Si with a 2 nm thick NbN film. Functional devices based on NbN films of such thickness were fabricated for the first time due to an improvement of superconducting properties of NbN film deposited on MgO buffer layer on Si substrate. Introduction. In the last years, the development of HEB mixers has reached such a high level that these devices can be successfully utilized in heterodyne receivers of THz frequency range. Their high sensitivity and low LO power make them suitable for radioastronomic observations on space- and airbom platforms. An NbN HEB mixer seems to be a

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Superconducting NbN Hot Electron Bolometer with an Nb5N6 Buffer Layer

Daogang Sun, Hongkai Shi, Runfeng Su +6 more

In this paper, the superconducting NbN hot electron bolometer terahertz detector with an Nb5N6buffer layer was fabricated on the Si substrate. The Nb5N6buffer layer can significantly improve the superconductivity of ultra-thin NbN films. Preliminary results show that with a 30-nm-thick buffer, the zero resistance superconducting transition temperature of a 6-nm-thick NbN film device is 12.6 K, and the superconducting critical current of the device is increased by four times. The noise temperature, IF bandwidth and direct detection sensitivity of the device will be further characterized in following experiments.

International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)•Nov 8, 2020•1 citation

IF bandwidth and noise temperature measurements of NbN HEB mixers on MgO substrates

Shigehito Miki, Yoshinori Uzawa, Akira Kawakami +1 more

We report the fabrication and testing of hot electron bolometric mixers with an ultrathin NbN film as heterodyne receivers operating at terahertz frequencies. We found that the quality of the NbN strip is usually degraded by damage resulting from the fabrication process, and we developed a process for reducing such damage. We also fabricated HEB mixers with a new structure in order to study the IF bandwidth determined by the original quality of the NbN thin films. Investigations at 100 GHz revealed that the widest IF bandwidth of 2.0 GHz was obtained by a mixer based on a 2.8 nm-thick NbN film. An HEB mixer based on the 2.8 nm-thick NbN film was also fabricated and evaluated. The receiver noise temperature at 900 GHz was 780 K, the absorbed LO power was about 400 nW, and the conversion gain was -13 dB.

IEEE Transactions on Applied Superconductivity•Mar 1, 2001•20 citations
We realized ultra thin NbN films sputtered grown on a 3C-SiC/Si substrate. The film with a thickness of 3.5-4.5 nm shows a 1', of 11.8 K, which is the highest I`, observed among ultra thin NbN films on different substrates. The high-resolution transmission electron microscopy (HRTEM) studies show that the film has a monocrystalline structure, confirming the epitaxial growth on the 3C-SiC. Based on a two-temperature model and input parameters from standard NbN films on Si, simulations predict that the new film can increase the IF bandwidth of a HEB mixer by about a factor of 2 in comparison to the standard films. In addition, we find standard NbN films on Si with a T c of 9.4 K have a thickness of around 5.5 nm, being thicker than expected (3.5 nm).
The key of improving hot-electron bolometer (HEB) mixer performance lies inevitably in the quality of ultra-thin NbN films itself. This work presents a thorough investigation of crucial process parameters of NbN films deposited by means of reactive DC-sputtering on Si-substrates at elevated temperatures up to 750°C.The polycrystalline NbN films with thickness of 4 to 10nm were characterized by DC resistivity measurements, ellipsometry and high resolution transmission electron microscopy (HRTEM) in order to confirm thickness and film structure. Since the macroscopic properties such as critical temperature, thickness as well as the transition width to the superconducting state are directly linked to HEB mixer noise temperature and IF bandwidth, a set of experiments were conducted to enhance aforementioned properties. We considered deposition temperature, RF biasing, nitrogen and argon partial and total pressure during deposition as major process variable parameters. Careful optimization of the deposition conditions allowed setting up a process resulting in high-quality NbN ultra-thin films with thickness of 5.5nm exhibiting Tc of 10.5K. Moreover, the transition width could be kept as low as 1.4K. The produced films were stored at ambient conditions and re-characterized over a period of 4 month without measurable degradation.
In this paper, we present a reliable measurement method to study the influence of the GaN buffer layer on phonon-escape time in comparison with commonly used Si substrates and, in consequence, on the IF bandwidth of HEBs. One of the key aspects is to operate the HEB mixer at elevated bath temperatures close to the critical temperature of the NbN ultra-thin film, where contributions from electron-phonon processes and self-heating effects are relatively small, therefore IF roll-off will be governed by the phonon-escape.Two independent experiments were performed at GARD and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. The entire IF chain was characterized by S-parameter measurements. We compared the measurement results of epitaxial NbN grown onto GaN buffer-layer with Tc of 12.5 K (4.5 nm) with high quality polycrystalline NbN films on Si substrate with Tc of 10.5 K (5 nm) and observed a strong indication of an enhancement of phonon escape to the substrate by a factor of two for the NbN/GaN material combination.
Abstract As part of an effort to develop heterodyne rf receivers operating in the terahertz band, we have fabricated hot‐electron bolometers (HEB) using NbN thin films, and investigated their intermediate frequency (IF) bandwidths. The NbN thin films we studied were grown on single‐crystal MgO substrates by dc reactive sputtering. Our 2.8‐nm‐thick films exhibited superior superconducting properties, including transition temperatures TC of 9.7 K and 20 K resistivities ρ20 of 185 µΩ·cm. Using electron beam diffraction, high‐resolution TEM images, and other techniques to study the crystallinity of these films, we determined that the NbN grows epitaxially on the MgO substrate as single‐crystal material. The HEB elements we made consisted of a NbN microstrip, a Au electrode section, and an Al antenna section. In the course of studying the IF bandwidths of these devices in the millimeter‐wave range, we found one device with an IF bandwidth of 2.5 GHz, the highest of any device we made. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(7): 77–83, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecjb.1111
We present recently obtained values for gain bandwidth of NbN HEB mixers for different substrates and film thicknesses and for MgO buffer layer on Si at LO frequency of 0.85-1 THz. The maximal bandwidth, 5.2 GHz, was achieved for the device on MgO buffer layer on Si with a 2 nm thick NbN film. Functional devices based on NbN films of such thickness were fabricated for the first time due to an improvement of superconducting properties of NbN film deposited on MgO buffer layer on Si substrate. Introduction. In the last years, the development of HEB mixers has reached such a high level that these devices can be successfully utilized in heterodyne receivers of THz frequency range. Their high sensitivity and low LO power make them suitable for radioastronomic observations on space- and airbom platforms. An NbN HEB mixer seems to be a
In this paper, the superconducting NbN hot electron bolometer terahertz detector with an Nb5N6buffer layer was fabricated on the Si substrate. The Nb5N6buffer layer can significantly improve the superconductivity of ultra-thin NbN films. Preliminary results show that with a 30-nm-thick buffer, the zero resistance superconducting transition temperature of a 6-nm-thick NbN film device is 12.6 K, and the superconducting critical current of the device is increased by four times. The noise temperature, IF bandwidth and direct detection sensitivity of the device will be further characterized in following experiments.
We report the fabrication and testing of hot electron bolometric mixers with an ultrathin NbN film as heterodyne receivers operating at terahertz frequencies. We found that the quality of the NbN strip is usually degraded by damage resulting from the fabrication process, and we developed a process for reducing such damage. We also fabricated HEB mixers with a new structure in order to study the IF bandwidth determined by the original quality of the NbN thin films. Investigations at 100 GHz revealed that the widest IF bandwidth of 2.0 GHz was obtained by a mixer based on a 2.8 nm-thick NbN film. An HEB mixer based on the 2.8 nm-thick NbN film was also fabricated and evaluated. The receiver noise temperature at 900 GHz was 780 K, the absorbed LO power was about 400 nW, and the conversion gain was -13 dB.