1. HIFI Mixer CDR Band 3 and 4 Mixer Units RF Design and Performance SRON B. Jackson, G. de Lange, W. Laauwen, L. de Jong DIMES, TU Delft T. Zijlstra, M. Kroug, M. Zuidam, N. Iosad, B. de Lange, J.R. Gao, T.M. Klapwijk

2. Outline requirements historical overview prototype mixers: design and performance –waveguide mixer –quasi-optical mixer development model program –waveguide mixer re-design –measured performance flight model program –band 3 design –band 4 design conclusions and current status

3. Required Sensitivity T N,DSB (mixer + IF)

4. Historical Overview 1998-1999 –integration of Nb SIS with NbTiN tuning circuits at RUG –pre-existing mask-set, full-height 1 THz mixer 1999-2000 –implementation of SIS 13 (WG) and SIS 14 (QO) masks at RUG –NbTiN/SiO 2 /NbTiN vs. NbTiN/SiO 2 /Al tuning circuits –NbTiN/SiO 2 /Al → low-noise mixers up to 1 THz 2000-2001 –redesign of WG mixer → ccn5 and SIS 19 mask designs –re-establishment of SIS process at DIMES 2001-2002 –implementation of SIS 19 mask at DIMES –demonstration of broad-band, low-noise performance in band 3 2002 –FM designs: SIS 20 (band 3) and SIS 21 (band 4)

5. WG Mixer Prototype, 1 tunable and fixed-tuned 1 THz mixers –pre-existing full-height waveguide + diagonal horn single- and twin-junction designs –Nb SIS, NbTiN/SiO 2 /NbTiN and NbTiN/SiO 2 /Al tuning circuits NbTiN/SiO 2 /NbTiNNbTiN/SiO 2 /Al

6. WG Mixer Prototype, 2 NbTiN/SiO 2 /NbTiNNbTiN/SiO 2 /Al

7. QO Mixer Prototype quasi-optical lens-antenna –twin-slot, double-dipole antennas –10 mm elliptical lens, AR-coated twin-junction tuning circuit –Nb SIS + NbTiN/SiO 2 /Al –low receiver noise to 1 THz

8. Prototype Mixers, Conclusions microstrip geometry –heat-trapping, flux-trapping, and excess RF loss in NbTiN/SiO 2 /NbTiN NbTiN/SiO 2 /Al preferred NbTiN ground-plane quality –room-temp. deposition “low-loss” to 1 THz –improvements needed for band 4 elevated-T or MgO substrate WG vs QO design –similar peak T N,mix+IF (190-230 K) –QO: ΔF RF > 200 GHz –WG: ΔF RF ~ 100 GHz –WG mixer redesign needed Calculated vs. Measured QO Mixer Response

9. DM Program, RF Design narrow RF bandwidth of prototype mixer due to non-optimized design scale 650 GHz JCMT mixer design (half-height waveguide) –RF geometry scaled to 880- and 1040-GHz band 3: WG = 300x75, BS = 60, channel = 75x55, substrate = 60x30 –“embedding impedance” needed for device design 650 GHz design modelled in HFSS by J. Kooi (CalTech) result scaled to 880 and 1040 GHz centre frequencies

10. DM Program, Device Designs band 3 –single- and twin-junctions –NbTiN/SiO 2 /Al tuning circuit –both designs: full RF bandwidth –twin-junction: better RF coupling band 4 –twin-junction designs only –NbTiN/SiO 2 /Al tuning circuit: 3 designs sensitive to NbTiN quality –Al/SiO 2 /Al tuning circuit: broad RF bandwidth reduced coupling

11. DM Program, Results 1 band 3 twin-junctions –strong, broad-band response RF bandwidth > 200 GHz F centre ~ 900 GHz F cut-off ~ 1 THz –DM = device c56

12. DM Program, Results 2 b3 twin-junction, c56: T N,mix+IF ~ 230-250 K (IF = 4-8 GHz, T bath = 2.5 K) A68 A67 C56 (DM) C65

13. DM Program, Results 3 B67 C31 Band 3 Single-JunctionBand 4, NbTiN/SiO 2 /Al

14. DM Program, Conclusions waveguide mixer redesign –half-height 880 and 1040 GHz mixers based on 650 GHz JCMT mixer –880 GHz twin-junction → low-noise performance covering band 3 –band 4 performance limited by NbTiN quality comparison with prototype QO mixer –DM WG: T N,mix+IF ~ 230-250 K over 4-8 GHz IF (T N,IF ~ 10 K) –QO: T N,mix+IF = 190-210 K at 850-980 GHz at 1.5 GHz IF (T N,IF ~ 4 K) extra noise for 4-8 GHz IF ~ 30-35 K (G mix ~ - 8-9 dB) other –low success rate for device mounting very low effective device yield need to increase device size for FM, if possible

15. FM Program, Band 3 Design modified DM design → enlarged substrate and substrate channel channel = 90x60, substrate = 75x35 (vs. 60x30), BS = 50 –resulting embedding impedance shifted slightly vs. DM design mounting using Al 2 O 3 carrier intrinsically suspends device –sensitivity of “embedding” to air gap reduced by intentional suspension channel = 90x87, substrate = 75x45, air gap = 17, BS = 25 “embedding impedances” calculated in HFSS by J. Kooi (CalTech) –results input to device design (as for DM design)

16. FM Program, Band 3 Design twin-junctions only, Nb SIS + NbTiN/SiO 2 /Al tuning circuit two designs (“modified” and “suspended”) –“modified” design: equivalent to “DM” (small changes to transformer) –“suspended” design: less frequency-dependent than “DM” predicted performance –J c = 8 kA/cm 2 → similar to DM –J c = 10-15 kA/cm 2 → improvement possible, depending upon junction quality

17. FM Program, Band 4 Design improved NbTiN quality needed –NbTiN deposited at elevated temperature at JPL, devices processed at DIMES T c = 15.5-16.0 K, ρ n, 20K = 60 µΩ·cm RF design –scaled band 3 “suspended” design only (available design variation used for NbTiN properties, production tolerances) device design –RF properties of NbTiN uncertain → 3 basic designs F gap = 1095 GHz, ρ n = 100 µΩ·cm F gap = 1135 GHz, ρ n = 77 µΩ·cm F gap = 1175 GHz, ρ n = 60 µΩ·cm predicted performance –similar to band 3 design (calculated RF coupling ~ 50 % vs. 55 %)

18. Conclusions prototype program –NbTiN/SiO 2 /NbTiN + Nb SIS → heat-trapping, RF loss above 900 GHz –NbTiN/SiO 2 /Al tuning circuit → high sensitivity up to 1 THz T N,mix+IF ~ 190-230 K (1.5 GHz IF, T N,IF ~ 4 K) DM program –redesign of RF geometry yields desired RF bandwidth in Band 3 –noise performance similar to prototype mixers DM: T N,rec = 350 K, T N,mix+IF ~ 240 K (4-8 GHz IF, T N,IF ~ 10 K) FM –redesign of band 3 RF design to ease device mounting, improve yield increased substrate size, suspended substrate expected band 3 performance equal to DM (J c = 8 kA/cm 2 ), or better –improved NbTiN quality needed in band 4 NbTiN ground planes obtained from JPL, processed at DIMES performance comparable to band 3 DM is expected

19. Current Status T N,DSB (mixer + IF)