Large scale 2D SQIF arrays Shane T Keenan CSIRO, Sydney, Australia EUCAS, 18 th September 2017 E Mitchell, K Hannam, J Lazar, C Lewis, A Grancea, K Wilson, B Vasilevski, W Purches and C Foley MANUFACTURING Supported by the Department of Defence Science and Technology Group (DSTG), through the CTD programme
Outline YBCO step-edge junctions Brief SQIF overview 2D SQIF arrays with high-t c step-edge Josephson junctions 20,000 JJ design Effective of reducing bl on V-B response 100,000 JJ design LN2 cooled vs mechanical cryo-cooler, Temperature dependence measurements, Field cooled unshielded performance, RF near-field and far-field measurements. 1,000,000 JJ design Summary and Future work 2
YBCO Step-Edge Josephson junctions 50nm Junction width 1-2nm Atomic alignment of a-b planes 20nm GBJ CSIRO patented high T c junction technology Large I c R n products Low I c noise fluctuations Good B-field performance Cheap, long term stability C. P. Foley et al, IEEE Trans. Appl. Supercond. 9 (1999) 4281. E.E. Mitchell and C.P. Foley, SUST. 23 (2010) 065007 Standard parameters in array designs: w = 2 mm, I c 20 ma, R n 5-7 W Scalable and can impedance match array to output, say 50 W Versatile for 1D and 2D arrays - place junctions anywhere on the substrate 3
SQIFs: Overview Single dc SQUID Periodic V-B 2 slit interference SQUID array SQUIDs coupled together in-parallel Diffraction grating. SQIF array different loop sizes single anti-peak at zero field V-B response. 4
SQIFs: Overview Single dc SQUID SEJ ~100 V/T 50 mv 2D SQIF array different loop areas Sensitivity depends on loop areas, spread, N, L, I c 1.5 kv/t 0.9 mv Improvements to: Sensitivity dv/db Linearity Dynamic range 5 Frequency response Bias @ V B = max
2D SQIF designs - 20,000 Junctions Initial design D1 20 x 2D sub-arrays connected in series, each with 1000 junctions N B = 20, N s = 20 (400), N p = 50. Pseudo-random flat area distribution, ~ 65% spread Mean area 280 µm 2, β L 1 (I c 20 μa) Sensitivity 1,530 V/T at 77 K Linear increase in sensitivity E.E. Mitchell et al., Supercond. Sci. Technol. 29 (2016) 06LT01 6
Effect of b L on sensitivity β L = 2LI c ~1 for dc SQUID φ 0 Previous results 1 indicate b L <1 better for SQIFs. Reducing mean loop area to reduce inductance L Design D1-280 mm 2 - L AV 51.2 ph b L ~1 280 mm 2 90 mm 2, pseudo-random s A 65 % 1 E.E. Mitchell et al., Supercond. Sci. Technol. 29 (2016) 06LT01 Design D2-30 mm 2 - L AV 21.5 ph b L ~0.4 30 mm 2 7 mm 2, Gaussian s A 45 % b L ~1 b L ~0.4 7 40 mm
1. Effect of b L ~ 1 and ~0.4 with N = 20,000 arrays Design D2 Lower b L produces: Higher sensitivity Larger DV Design D1 Array b L s A % Average V p-p (mv) Average V B (kv/t) Design D1 (JL338) 1.0 65 1.8 2.85 - Design D2 8 (WP010) 0.4 45 Gain 6.6 6.35 2.2
2D SQIF designs 100,200 Junctions Design D3 Junction number increased to N = 100,200. Six 2D sub-arrays connected in series, each with 16,700 junctions. N b = 6, N s =167 (1,002), N p = 100, Mean area 30 µm 2, β L = 0.4 (I c = 20 μa). Gaussian distribution, s A = 45% spread. Sub-arrays 9
Comparing 100,200 JJ arrays @ 77 K 5 x 100,200 JJ devices fabricated same design Array # V p-p (mv) V B (kv/t) JL335 23.4 20.5 JL336 20.5 18.2 JL345 17.6 24.8 JL346 29.4 30.8 JL353 29.8 29.8 Average 24.1 24.8 10
Array Design # Comparison of SQIF Array designs at 77 K N σ A % A av (μm 2 ) L av (ph) β L (for I c = 20 µa) Average V p-p (mv) Average V B (kv/t) Improvement over previous D1 20,000 65 280 ± 90 51.2 1.0 1.8 2.85 - D2 20,000 45 30 ± 7 21.5 0.4 6.6 6.35 2.2 D3 100,200 45 30 ± 7 21.5 0.4 24.8 24.8 3.9 20k JJ bl~ 1.0 20k JJ bl~ 0.4 100k JJ bl~ 0.4 11
Cryo-cooled SQIF arrays SQIFs integrated into a miniature single-stage Stirling cycle cryo-cooler. Sunpower DS miniature cryocoolers. Compact and lightweight < 7 Kg (total), dimensions: 35 cm x 18 cm x 12 cm. Low power requirements 30 W input Battery operated 13 hours run time/charge 20 cm 1 cm 2 chip mounted on AlN substrates high thermal conductivity, non-metallic. Device orientated vertically and typically B E 12
Cryo-cooled vs LN 2 cooled SQIF has comparable performance cooled unshielded on the cryo-cooler vs shielded LN 2. Averaged V-B response shown - No suppression of curve EM interference from cryocooler not in band of interest for RF measurements 60 Hz. 13
Temperature dependence of SQIF array Temperature significantly effects the I C and L of the device (a) I C increases and L decreases with T. (b) V B, DV optimized. (c) Shape of V-B changes with T(K)- suggesting different loop contributions Array # JL336 V p-p (mv) V B (kv/t) @ 77 K 18.2 20.5 optimum V p-p @ 66 K 35.5 36.5 optimum V B @ 70 K 32.8 39 14
Voltage [V] Unshielded performance - Zero field cooled (ZFC) Field applied (FA) JL336 - (100,200 JJ array) operated at 70 K completely unshielded on a cryo-cooler. Cooled with sensitive axis to B E Two Helmholtz field coils used first for V-B field sweep 60 mt, second for dc field applied 50 mt 0.110 0.105 0.100 0.095 B FA 0.090 0.085 B V-B SQIF array 0.080 0.075-100 -50 No suppression of V-B curve. Works well as absolute field sensor 0 50 Magnetic field [mt] 100 15
RF far-field detection of AM radio band using HTS SQIF HTS SQIF array with N = 100,200 To show that the signals were from the SQIF, the array was biased at constant current and instead the magnetic bias was changed. Local AM radio stations appear when the arrays are magnetically biased on (a), and disappear when biased off (b). (a) (b) AM stations 16
N = 1,012,500 array#1 More than one million junctions Increase MgO substrate size to 4cm 2 N b =9, N s =500 (4500), N p = 225, V B = 40.1 kv/t and DV = 53.3 mv But lower than expected due to poorer YBCO film properties 17 2cm
Summary HTS SQIF arrays extended from N =20,000 to 1,000,000. SQIF sensitivity increases with decreasing b L and increasing N. Sensitivities of 30.8 kv/t for N = 100,200 up to 39 kv/t cryo-cooled. RF detection of AM radio stations up to 1.5MHz demonstrated using HTS SQIF Fabrication of SQIF arrays with N = 1,000,000 and 40.1 kv/t; expect more. Watch this space. 18
Future Work Push sensitivity further! Develop models for thin film HTS structures with (L, M, l L ), including JJs. Better control of inter-batch variations in YBCO film properties. Increase frequency span for RF measurements Thanks to the Australian Department of Defence Science and Technology Group for their support of this research through the CTD programme. 19
IWSSD 2018 invitation! 4 th international workshop on Superconducting Sensors and detectors July 24-27 th 2018 Sydney, Australia Website currently under development.. https://events.csiro.au/events/2017/september/11/4th-superconducting-sensors-and-detectors 20
CSIRO SQIF Team Thank you CSIRO Manufacturing Lindfield, NSW Australia Shane Keenan Shane.keenan@csiro.au www.csiro.au Emma Mitchel Jeina Lazar Alex Grancea Shane Keenan Wendy Purches Chris Lewis Bill Vasilevski Karl Wilson Cathy Foley MANUFACTURING
Voltage [V] Voltage [V] Voltage [V] Voltage [V] Field cooled (FC) Field applied (FA) 0.110-10 mt 0 mt 0.105 0.100 0.095 0.090 0.085 0.080 0.075-100 10 mt 20 mt 30 mt 40 mt 50 mt 0 50-50 Magnetic field [mt] 100 0.110-20 mt -10 mt 0.105 0.100 0.095 0.090 0.085 0.080 0.075-100 0 mt 10 mt 20 mt 30 mt 40 mt 50 mt 0 50-50 Magnetic field [mt] 100 0.110 0.105 0.100 0.095 0.090 0.085 0.080 0.075-100 0 50-50 Magnetic field [mt] 100 0.110 0.105 0.100 0.095 0.090 0.085 0.080 0.075-100 -30 mt -20 mt -40 mt -10 mt 0 mt 10 mt 20 mt 30 mt 40 mt -30 mt -20 mt -10 mt 0 mt 10 mt 20 mt 30 mt 0 50-50 Magnetic field [mt] 100 22
RF flat-band response for SQIF with N=100K (a) (b) Parasitic contributions removed by subtracting SQIF-on and SQIF-off response SQIF amplitude (a) attributed to the RF source coil s inductive reactance, which was modelled and subtracted (b) Less than 4 db variation between 10-300 MHz frequency span 23