Program and Abstract Book - SRON
Program and Abstract Book - SRON
Program and Abstract Book - SRON
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19 th International Symposium on Space Terahertz Technology<br />
P2-1<br />
Superconducting contacts <strong>and</strong> NbN HEB mixers performance<br />
T. Bansal 1,2 , P. Khosropanah 2 , W. Zhang 2,3 , J.R. Gao 1,2 , T.M. Klapwijk 1 ,<br />
1 Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherl<strong>and</strong>s<br />
2 <strong>SRON</strong> Netherl<strong>and</strong>s Institute for Space Research, Utrecht/Groningen, The Netherl<strong>and</strong>s<br />
3 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, P.R. China<br />
email:T.bansal@tudelft.nl<br />
Phonon-cooled superconducting NbN hot electron bolometer (HEB) mixers are so far the<br />
only sensitive heterodyne detector at high frequencies beyond 1.5 THz. It is known that<br />
under operating conditions the parabolic electron temperature set up due to the absorbed LO<br />
power depends on the boundary conditions, related to the contact pads. 1 Earlier, we have<br />
reported that the sensitivity of such a mixer can depend on contact materials. The best<br />
sensitivities have been obtained by using a NbTiN superconductor layer between thin NbN<br />
<strong>and</strong> Au in the contacts. 2,3<br />
In this work we replace the 10nm thick NbTiN with 10 nm thick Nb. The motivations are: a)<br />
Gain a new insight of the role of the contacts <strong>and</strong> ultimately the physics; b) Nb process is<br />
much more widely available; c) Establish a more reproducible fabrication process.<br />
We have succeeded in realizing HEB mixers using both contacting materials on a single<br />
wafer with the same fabrication steps except for the contacting materials. The bolometer is<br />
based on a typical thin NbN film 4 grown on a Si substrate with a critical temperature of 9.5<br />
K. The bolometer has a dimension of 0.2 μm×2 μm <strong>and</strong> is terminated by a spiral antenna<br />
with an upper cut-off frequency of ~6 THz. We are currently evaluating the heterodyne<br />
performances of both types of mixers. The first device of HEBs with Nb contacts has<br />
demonstrated a DSB receiver noise temperature of 1230 K at 2.5 THz at the optimal LO<br />
power (190 nW) <strong>and</strong> bias <strong>and</strong> using an uncoated Si lens. This value was measured directly by<br />
recording the output noise power responding to hot/cold loads at the same bias current 5 . If we<br />
correct the loss due to the absence of the antireflection coating, we expect to reduce this<br />
noise temperature to 980 K, which is practically same as the best performance reported at this<br />
frequency from a NbTiN contacted HEB previously 2 .<br />
References:<br />
1. R. Barends, M. Hajenius, J. R. Gao, T.M. Klapwijk, “Current inducd vortex unbinding in bolometer mixers”, Appl.<br />
Phys. Lett, 87, 263506 (2005).<br />
2. M. Hajenius, J. J. A. Baselmans, J. R. Gao, T.M. Klapwijk, P. A. J. de Korte, B. Voronov <strong>and</strong> G. Gol’tsman, “Low<br />
noise NbN superconducting hot electron bolometer mixers at 1.9 <strong>and</strong> 2.5 THz”, Supercond. Sci. Technol. 17, S224–<br />
S228 (2004).<br />
3. J. J. A. Baselmansa, M. Hajenius, J. R. Gao, T. M. Klapwijk, P. A. J. de Korte, B. Voronov <strong>and</strong> G. Gol’tsman<br />
“Doubling of sensitivity <strong>and</strong> b<strong>and</strong>width in phonon cooled hot electron bolometer mixers” Appl. Phys. Lett, 84, 1958-<br />
1961 (2004).<br />
4. The NbN thin film was provided by SCONTEL, Moscow, Russia ( http:/www.scontel.ru).<br />
5. P. Khosropanah, J. R. Gao, W. M. Laauwen, M. Hajenius, <strong>and</strong> T. M. Klapwijk, “ Low noise NbN hot electron<br />
bolometer mixer at 4.3 THz”, Appl. Phys. Lett. 91, 221111 (2007).<br />
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