Bias sputtered NbN and superconducting nanowire devices
Superconducting nanowire single photon detectors (SNSPDs) promise to combine near-unity quantum efficiency with >100 megacounts per second rates, picosecond timing jitter, and sensitivity ranging from x-ray to mid-infrared wavelengths. However, this promise is not yet fulfilled, as superior perfo...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
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AIP Publishing
2020
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| Online Access: | https://hdl.handle.net/1721.1/126227 |
| _version_ | 1826188061887692800 |
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| author | Dane, Andrew Edward McCaughan, Adam N Zhu, Di Zhao, Qingyuan Kim, Chungsoo Calandri, Niccolo Agarwal, Akshay Bellei, Francesco Berggren, Karl K |
| author2 | Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science |
| author_facet | Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science Dane, Andrew Edward McCaughan, Adam N Zhu, Di Zhao, Qingyuan Kim, Chungsoo Calandri, Niccolo Agarwal, Akshay Bellei, Francesco Berggren, Karl K |
| author_sort | Dane, Andrew Edward |
| collection | MIT |
| description | Superconducting nanowire single photon detectors (SNSPDs) promise to combine near-unity quantum efficiency with >100 megacounts per second rates, picosecond timing jitter, and sensitivity ranging from x-ray to mid-infrared wavelengths. However, this promise is not yet fulfilled, as superior performance in all metrics is yet to be combined into one device. The highest single-pixel detection efficiency and the widest bias windows for saturated quantum efficiency have been achieved in SNSPDs based on amorphous materials, while the lowest timing jitter and highest counting rates were demonstrated in devices made from polycrystalline materials. Broadly speaking, the amorphous superconductors that have been used to make SNSPDs have higher resistivities and lower critical temperature (Tc) values than typical polycrystalline materials. Here, we demonstrate a method of preparing niobium nitride (NbN) that has lower-than-typical superconducting transition temperature and higher-than-typical resistivity. As we will show, NbN deposited onto unheated SiO2 has a low Tc and high resistivity but is too rough for fabricating unconstricted nanowires, and Tc is too low to yield SNSPDs that can operate well at liquid helium temperatures. By adding a 50 W RF bias to the substrate holder during sputtering, the Tc of the unheated NbN films was increased by up to 73%, and the roughness was substantially reduced. After optimizing the deposition for nitrogen flow rates, we obtained 5 nm thick NbN films with a Tc of 7.8 K and a resistivity of 253 μΩ cm. We used this bias sputtered room temperature NbN to fabricate SNSPDs. Measurements were performed at 2.5 K using 1550 nm light. Photon count rates appeared to saturate at bias currents approaching the critical current, indicating that the device's quantum efficiency was approaching unity. We measured a single-ended timing jitter of 38 ps. The optical coupling to these devices was not optimized; however, integration with front-side optical structures to improve absorption should be straightforward. This material preparation was further used to fabricate nanocryotrons and a large-area imager device, reported elsewhere. The simplicity of the preparation and promising device performance should enable future high-performance devices. |
| first_indexed | 2024-09-23T07:54:00Z |
| format | Article |
| id | mit-1721.1/126227 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T07:54:00Z |
| publishDate | 2020 |
| publisher | AIP Publishing |
| record_format | dspace |
| spelling | mit-1721.1/1262272022-09-23T09:30:40Z Bias sputtered NbN and superconducting nanowire devices Dane, Andrew Edward McCaughan, Adam N Zhu, Di Zhao, Qingyuan Kim, Chungsoo Calandri, Niccolo Agarwal, Akshay Bellei, Francesco Berggren, Karl K Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science Superconducting nanowire single photon detectors (SNSPDs) promise to combine near-unity quantum efficiency with >100 megacounts per second rates, picosecond timing jitter, and sensitivity ranging from x-ray to mid-infrared wavelengths. However, this promise is not yet fulfilled, as superior performance in all metrics is yet to be combined into one device. The highest single-pixel detection efficiency and the widest bias windows for saturated quantum efficiency have been achieved in SNSPDs based on amorphous materials, while the lowest timing jitter and highest counting rates were demonstrated in devices made from polycrystalline materials. Broadly speaking, the amorphous superconductors that have been used to make SNSPDs have higher resistivities and lower critical temperature (Tc) values than typical polycrystalline materials. Here, we demonstrate a method of preparing niobium nitride (NbN) that has lower-than-typical superconducting transition temperature and higher-than-typical resistivity. As we will show, NbN deposited onto unheated SiO2 has a low Tc and high resistivity but is too rough for fabricating unconstricted nanowires, and Tc is too low to yield SNSPDs that can operate well at liquid helium temperatures. By adding a 50 W RF bias to the substrate holder during sputtering, the Tc of the unheated NbN films was increased by up to 73%, and the roughness was substantially reduced. After optimizing the deposition for nitrogen flow rates, we obtained 5 nm thick NbN films with a Tc of 7.8 K and a resistivity of 253 μΩ cm. We used this bias sputtered room temperature NbN to fabricate SNSPDs. Measurements were performed at 2.5 K using 1550 nm light. Photon count rates appeared to saturate at bias currents approaching the critical current, indicating that the device's quantum efficiency was approaching unity. We measured a single-ended timing jitter of 38 ps. The optical coupling to these devices was not optimized; however, integration with front-side optical structures to improve absorption should be straightforward. This material preparation was further used to fabricate nanocryotrons and a large-area imager device, reported elsewhere. The simplicity of the preparation and promising device performance should enable future high-performance devices. NASA (Grant NNX14AL48H) 2020-07-16T19:41:00Z 2020-07-16T19:41:00Z 2017-09 2017-06 Article http://purl.org/eprint/type/JournalArticle 0003-6951 1077-3118 https://hdl.handle.net/1721.1/126227 Dane, Andrew E. et al. "Bias sputtered NbN and superconducting nanowire devices." Applied Physics Letters 111, 12 (September 2017): 122601. http://dx.doi.org/10.1063/1.4990066 Applied Physics Letters Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf AIP Publishing Prof. Berggren via Phoebe Ayers |
| spellingShingle | Dane, Andrew Edward McCaughan, Adam N Zhu, Di Zhao, Qingyuan Kim, Chungsoo Calandri, Niccolo Agarwal, Akshay Bellei, Francesco Berggren, Karl K Bias sputtered NbN and superconducting nanowire devices |
| title | Bias sputtered NbN and superconducting nanowire devices |
| title_full | Bias sputtered NbN and superconducting nanowire devices |
| title_fullStr | Bias sputtered NbN and superconducting nanowire devices |
| title_full_unstemmed | Bias sputtered NbN and superconducting nanowire devices |
| title_short | Bias sputtered NbN and superconducting nanowire devices |
| title_sort | bias sputtered nbn and superconducting nanowire devices |
| url | https://hdl.handle.net/1721.1/126227 |
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