Development of an Inductive NIS Thermometer

This is an elec onic ep in o he o iginal a icle. This ep in may di e om he o iginal in pagina ion and ypog aphic de ail. Au ho (s): Ti le: Yea : Ve sion: Please ci e he o iginal e sion: All ma e ial supplied ia JYX is p o ec ed by copy igh and o he in ellec ual p ope y igh s, and duplica ion o sale o all o pa o any o he eposi o y collec ions is no pe mi ed, excep ha ma e ial may be duplica ed by you o you esea ch use o educa ional pu poses in elec onic o p in o m. You mus ob ain pe mission o any o he use. Elec onic o p in copies may no be o e ed, whe he o sale o o he wise o anyone who is no an au ho ised use . De elopmen o an Induc i e NIS The mome e Geng, Zhuo an; Kinnunen, Kimmo; Maasil a, Ila i Geng, Z., Kinnunen, K., & Maasil a, I. (2012). De elopmen o an Induc i e NIS The mome e . In 26 h In e na ional Con e ence on Low Tempe a u e Physics (LT26) 10–17 Augus 2011, Beijing, China (pp. 52005). Ins i u e o Physics. Jou nal o Physics: Con e ence Se ies, 400. h ps://doi.o g/10.1088/1742-6596/400/5/052005 2012 This con en has been downloaded om IOPscience. Please sc oll down o see he ull ex . Download de ails: IP Add ess: 130.234.75.141 This con en was downloaded on 15/01/2016 a 10:43 Please no e ha e ms and condi ions apply. De elopmen o an Induc i e NIS The mome e View he able o con en s o his issue, o go o he jou nal homepage o mo e 2012 J. Phys.: Con . Se . 400 052005 (h p://iopscience.iop.o g/1742-6596/400/5/052005) Home Sea ch Collec ions Jou nals Abou Con ac us My IOPscience De elopmen o an Induc i e NIS The mome e Z. Geng, K. M. Kinnunen and I. J. Maasil a Nanoscience Cen e , Depa men o Physics, P.O. Box 35, FI-40014 Uni e si y o Jy ¨askyl¨a, Finland E-mail: [email p o ec ed] Abs ac . We ha e s udied an induc i e eadou o no mal me al-insula o -supe conduc o (NIS) unnel junc ions by using on-chip plana induc o s and a DC SQUID (supe conduc ing quan um in e e ence de ice) o de elop a sensi i e and as he mome e o s udies o nanoscale hea conduc ion and bolome y. Ou ini ial esul s show he easibili y o he concep , wi h a good sensi i i y o empe a u es below 1 K o aluminum as he supe conduc o when ol age biased close o he supe conduc o ene gy gap. 1. In oduc ion The desi e o sensi i e bolome e s has encou aged people o de elop as esponse, low empe a u e and nanoscale no mal me al-insula o -supe conduc o (NIS) unnel junc ion he mome e s which can easily be in eg a ed in o an enna and abso be s uc u es o o m he bolome e s uc u e [1–3]. Such a de ice has s ong empe a u e-dependen cu en - ol age cha ac e is ics, submic on size, low sel hea ing and na u al bandwid h up o ew MHz[4], and has been used ex ensi ely in s udies o low- empe a u e he mal anspo [5–7]. I is also an a ac i e candida e o a -in a ed bolome y applica ions [8]. Howe e , in all p e ious applica ions he NIS he mome e is wo king unde cons an cu en bias wi h a measu emen o he empe a u e dependence o he ol age (o esis ance) ac oss he unnel junc ion V(T) [9]. In con as , in his s udy we ha e ab ica ed a no el on-chip sub-Kel in symme ic SINIS he mome e , which is biased wi h DC ol age and ead ou using ou on-chip plana induc o s o ampli y and induc i ely couple he cu en signal o a DC SQUID moun ed on he 1 K s age o he e ige a o . By using his me hod, we can measu e he conduc ance bias and he empe a u e dependence o he conduc ance o he NIS unnel junc ions abo e audio equency ange and p e-ampli y he signal be o e he SQUID. 2. SINIS he mome e The basic p inciple o a NIS he mome e is based on he exis ence o he ene gy gap ∆ o he supe conduc ing elec ode. Ideally, a T→0, o low bias ol age |eV |<∆, elec ons canno unnel om he occupied s a es o he no mal me al o he supe conduc o because o he ene gy cos o c ea ing quasipa icle exci a ions. Howe e , when eV = ∆, quasipa icle injec ion becomes possible and unneling cu en will i s sha ply inc ease and hen becomes linea as a unc ion o V. Fo T > 0, he p esence o he mally exci ed elec ons in he no mal me al allows some elec ons o unnel a a lowe ol age, gi ing an exponen ial ail o he cu en in he egion below eV = ∆. This ail can be used in sensi i e he mome y. 26 h In e na ional Con e ence on Low Tempe a u e Physics (LT26) IOP Publishing Jou nal o Physics: Con e ence Se ies 400 (2012) 052005 doi:10.1088/1742-6596/400/5/052005 Published unde licence by IOP Publishing L d 1 In p ac ice, ypically wo NIS junc ions a e used in se ies symme ically (SINIS) in o de o double he signal esponsi i y, and hus he unneling cu en can be w i en as [10]: I(V, T) = 1 2eRTZ∞ −∞ nS(E)[ N(E−eV/2, TN)− N(E+eV/2, TN)]dE (1) whe e nS(E) is he supe conduc ing densi y o s a es (DOS) gi en by BCS heo y, N(E) is he Fe mi-Di ac dis ibu ion o he no mal me al island, TNis he empe a u e o no mal me al, Vis he ol age bias ac oss bo h junc ions and RTis he unneling esis ance o a junc ion, independen o Vand T. F om he equa ion we can see ha he I−Vcha ac e is ics, and he e o e also he conduc ance G(T) o he unnel junc ion, a e ela ed o he empe a u e o he no mal me al. This dependence is no mally measu ed unde a cons an cu en bias by measu ing he ol age esponse wi h a di e en ial ol age ampli ie a oom empe a u e [6]. In his expe imen , we ins ead bias he SINIS unnel junc ion wi h cons an ol age, and hen apply an 26 kHz equency exci a ion signal ac oss he unnel junc ion, and measu e he conduc ance di ec ly using a lock-in ampli ie , wi h an induc i ely coupled SQUID ampli ie a he 1 K s age as a p eampli ie s age, as shown in Fig.1. The po en ial bene i s o he SQUID eadou a e: (i) inc eased sensi i i y due o he low- empe a u e p eampli ie s age (ii) inc eased ead-ou bandwid h, as capaci i e loading o he wi ing is educed, and (iii) educed ex e nal noise hea ing adia ed down om he ead-ou ci cui . This las issue is ypically limi ing he ope a ional ange o SINIS he mome e s o >100 mK i no s ong measu es a e aken o il e he high- equency noise. Figu e 1. (a) Measu emen se up o his expe imen . AC and DC ol age signals a e applied o he SINIS unnel junc ion. Two ead ou s a e used, (i) di ec DC ead ou wi h one cu en p e- ampli ie and one ol age p e-ampli ie o measu e he DC IV cha ac e is ics o unnel junc ion (s anda d way), (ii) DC SQUID ead ou in combina ion wi h a on-chip ans o me o measu e he conduc ance o he junc ion using lock-in de ec ion. (b) SEM mic og aph o he sample. The uppe inse shows one NIS junc ion, he lowe inse shows he Niobium washe and coil. 3. Expe imen The SINIS unnel junc ion is ab ica ed wi h con en ional elec on beam li hog aphy (EBL) and shadow e apo a ion echniques in an ul a high acuum (UHV) chambe in o Al −AlOx−Cu− AlOx−Al s uc u e, wi h ilm hicknesses o 60 nm o Al and 80 nm o Cu. The junc ion size was 1 µm2and he AlOxwas o med by he mal oxida ion in pu e oxygen a mosphe e. Fou pai s o niobium inpu washe s ( hickness 60 nm) and ou pu coils ( hickness 120 nm) a e ab ica ed on he same chip wi h EBL and UHV e apo a ion, sepa a ed by a 200 nm HV deposi ed AlOxinsula o laye (Fig. 1) . A hin gold laye (6 nm) is used on he niobium laye o p e en oxidiza ion and o allow elec onic connec ion o he SINIS unnel junc ions and bonding pads. The sample we s udied has a o al unneling esis ance o RT= 800Ω, wi h 27.4 26 h In e na ional Con e ence on Low Tempe a u e Physics (LT26) IOP Publishing Jou nal o Physics: Con e ence Se ies 400 (2012) 052005 doi:10.1088/1742-6596/400/5/052005 2 nH ou pu coils, 400 pH inpu washe s and a measu ed coupling cons an o K= 0.83 be ween hem. The sample was measu ed in a compac dilu ion e ige a o wi h a base empe a u e o abou 50 mK. A wo s age DC SQUID ampli ie ab ica ed a NIST Boulde is also moun ed on he 1 K s age o he e ige a o and connec o he sample s age wi h supe conduc ing Nb-Ti wi es and supe conduc ing Al bonding wi es on he chip [11]. A calib a ed RuO he mome e is moun ed on he sample s age o moni o he s age empe a u e, and a me allic esis o is used as a hea e on he s age, so ha a PID con olle can s ablize he s age empe a u e. 4. Resul s Figu e 2. The empe a u e dependence o SINIS unnel junc ion conduc ance G(T) wi h a ying ba h empe a u e om 50 mK o 1 K om he SQUID and DC measu emen s. Di e en cu es co espond o di e en ba h empe a u es. Open ci cles: SQUID measu emen , lines DC measu emen . Inse : Zoom-in a he use ul ange o V. Figu e 2 shows he esul s o G(V) o bo h he s anda d DC measu emen s and SQUID measu emen s a ou di e en ba h empe a u es be ween 50 mK and 1 K. The solid lines in Figu e 2 a e he calcula ed conduc ance cu es om DC measu emen (nume ical di e en ia ion) and he open ci cles a e he SQUID measu emen esul s. The SQUID measu emen esul s ollow ex emely well he DC esul s o all empe a u es, showing ha ou measu emen scheme wo ks. The inse (b) shows he same conduc ance da a om 0.1 mV o 0.6 mV, which is he unc ional egime o ou he mome y. Figu e 3 gi es he empe a u e dependence o he SINIS unnel junc ion conduc ance G(T) om 50 mK o 1 K wi h di e en ol age biases om he SQUID measu emen . An in e es ing obse a ion is ha he e is a s ongly empe a u e-dependen egime below T < 0.2 K wi h opposi e esponsi i y (Ginc easing wi h T a he han dec easing as obse ed a T > 0.2 K) when he bias ol age is nea he supe conduc o ene gy gap ∆. This pa can be used as a e y sensi i e he mome e a empe a u es lowe han ∼0.2 K. We s ess ha his esponsi i y is s ill good a ou base empe a u e 50 mK, especially conside ing ha no il e s we e used in he measu emen wi es. In con as , in he highe empe a u e egime ( om 200 mK o 1 K), a lowe bias ol age will gi e a highe G(T) sensi i i y o he empe a u e, and hus one can choose i acco dingly. 26 h In e na ional Con e ence on Low Tempe a u e Physics (LT26) IOP Publishing Jou nal o Physics: Con e ence Se ies 400 (2012) 052005 doi:10.1088/1742-6596/400/5/052005 3 Figu e 3. G(T) o he SQUID measu emen . Di e en colo s co esponds o di e en bias ol ages be ween 0.05 mV o 0.4 mV. 2∆ is app oxima ely 0.45 mV. 5. Conclusions In conclusion, we ha e ab ica ed a SINIS unnel junc ion he mome e wi h an in eg a ed on- chip induc i e eadou coupled wi h a sensi i e SQUID ampli ie . Ou da a indica es ha i is easible o use his scheme o di ec ly measu e he conduc ance o SINIS unnel junc ion a audio equencies. The equency o ope a ion o his ype o de ice is no limi ed o audio equency ange, bu could possibly be ex ended o RF (up o ew MHz), whe e limi a ions o SQUID ampli ie and SINIS in e nal he mal ime cons an s a e me . Acknowledgmen s This wo k was suppo ed by he Academy o Finland p ojec no. 128532. Re e ences [1] Schmid D, Yung C S and Cleland A N 2003 Appl. Phys. Le . 83 1002 – 1004 [2] Schmid D R, Lehne K W, Cla k A M, Duncan W D, I win K D, Mille N and Ullom J N 2005 Appl. Phys. Le . 86 053505 [3] Chou ae D, Kuzmin L and Ta aso M 1999 Supe cond. Sci. Technol. 12 985–988 [4] Ki ioja J M, Maasil a I J, Pekola J P and Ka onen J T 2003 Physica E 18 21 – 22 [5] Ka onen J T and Maasil a I J 2007 Phys. Re . Le . 99 145503 [6] Koppinen P J and Maasil a I J 2009 Phys. Re . Le . 102 165502 [7] Meschke M, Guicha d W and Pekola J P 2006 Na u e (London) 444 187 – 190 [8] Schmid D, Duncan W, I win K, Lehne K, Mille N and Ullom J 2006 Nucl. Ins um. Me hods Phys. Res., Sec . A 559 516 – 518 [9] Giazo o F, Heikkil¨a T T, Luukanen A, Sa in A M and Pekola J P 2006 Re . Mod. Phys. 78 217 – 274 [10] Giae e I and Mege le K 1961 Phys. Re . 122 1101–1111 [11] Maasil a I J, Kinnunen K M, Nuo aj¨a i A K, Lepp¨aniemi J and Luukanen A 2006 Supe cond. Sci. Technol. 19 S242 – S245 26 h In e na ional Con e ence on Low Tempe a u e Physics (LT26) IOP Publishing Jou nal o Physics: Con e ence Se ies 400 (2012) 052005 doi:10.1088/1742-6596/400/5/052005 4