nist arda/dto review 2006 materials david p. pappas seongshik oh jeffrey kline
TRANSCRIPT
![Page 1: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/1.jpg)
NIST ARDA/DTO review2006
Materials
David P. Pappas
Seongshik Oh
Jeffrey Kline
![Page 2: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/2.jpg)
Materials Milestones• 3.1 First Year 3.1.1 Fabricated epitaxial aluminum for aluminum oxide junctions
AlOx barrier still amorphous
• 3.2 Second Year 3.2.1 Investigate new materials for superconducting electrodes
Lattice commensurability to the crystalline Al2O3 tunnel Refractory metals (Nb, Ta, Mo, W) – found Re engineered the epitaxial growth of Al2O3
• 3.3.1 Epitaxial barriers for junctions• All-epitaxial tunnel junctions will be fabricated in this phase of the program
• Sputter-deposited films, recrystallized by high temperature annealing on sapphire substrates.
• The tunnel barriers formed using the technique from second year
• Trilayers will then be processed into qubit devices
• Other barrier materials, such as nitrides, carbides and semiconductor materials.
![Page 3: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/3.jpg)
Frequency dependence of Qubits
Junction area 70 mm2
Amorphous barrier
Energy splittings can give rise to energy absorbtion!Reduces the measurement fidelity
![Page 4: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/4.jpg)
Density of splittings scales with junction size
13 um2 junction70 um2 junction
• Smaller area – Lower density, larger splitting (strong coupling)
• Larger area - Higher density, smaller splitting (weaker coupling)
![Page 5: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/5.jpg)
Two level fluctuators in junction
Amorphous AlO tunnel barrier
• Continuum of
metastable vacancies
• Changes on thermal cycling
I
![Page 6: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/6.jpg)
What we obtained:
Crystalline barrier-Al2O3
Poly - Al
Poly- Al
What we had:
Amorphous tunnel barrier a –AlOx – OH-
No spurious resonatorsStable barrier
Amorphous Aluminum oxide barrierSpurious resonators in junctionsFluctuations in barrier
Silicon
amorphous SiO2
Low loss substrate
Design of tunnel junctions
SC bottom electrode
Top electrode
Sapphire-Al2O3
![Page 7: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/7.jpg)
Chose bottom superconducting electrode to stabilize crystalline tunnel barrier - Al2O3 or MgO
Elements with high melting temperature
![Page 8: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/8.jpg)
Elements with TC > 1K
![Page 9: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/9.jpg)
Elements that lattice match insulator
• sapphire (Al203) - Nb, Ta, Mo, Tc, Re
• MgO - V
![Page 10: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/10.jpg)
Elements that form weaker bond with O than Al or Mg
![Page 11: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/11.jpg)
Elements that are not radioactive Mo or Re for Al2O3 barrier V for MgO tunnel barrier
![Page 12: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/12.jpg)
LEED, RHEED, AugerRe
Sputtering
LoadLock
STM/AFM
AlO
xyge
n
O2
Tests of Junction Materials
![Page 13: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/13.jpg)
Molybdenum film grown on a-plane sapphire
• As-grown (850C)– Narrow terraces– Some step bunching
• Post-growth anneal (1000C)– Broad terraces – More step bunching
400x400 nm2UHV050805.m4 400x400 nm2UHV050805.1.m6_p1
![Page 14: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/14.jpg)
Alumina barrier grown on Mo electrode
• As-grown (RT)– Granules present
JK05.4.m2_p1 AFM 2000x2000 nm2
1000x1000 nm2JK05.3.m3_p1 AFM
• After 850C post-growth anneal– Granules gone
![Page 15: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/15.jpg)
Pinholes in Al2O3 on MoPoor resistance to chemical etch
• Al2O3 / Re - resists SF6
Mo
Al2O3Al2O3
• Al2O3/Mo is etched rapidly
in SF6
Conclusion:
• Al2O3 grown on Mo has high pinhole density
• Agrees with electrical tests – poor electrical properties• => Try different template for growth - Re
SF6
SF6
Re
![Page 16: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/16.jpg)
Epitaxial growth of Re
• Low aspect hexagonal islands
• Mostly bilayer steps
• Reduces step inducedpinholes
Steps ~ 1 nm
![Page 17: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/17.jpg)
Growth of Epi-Re/Epi-Al2O3/Poly-Al
4×10-6 Torr O2, Al 10-6 Torr O2
Epitaxial Re/Al2O3
Re
@ 850 CAl
Amorphous AlOx
@ RT
Epitaxial Al2O3
@ 800 C
Polycrystalline Al
![Page 18: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/18.jpg)
Re/Al2O3/AlSmooth, crystalline interfaces
Re
Al
TEM cross section
Elemental resolution
2 nm
![Page 19: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/19.jpg)
Re
Al
Josephson Junction with a single-crystal Al2O3Tunnel barrier
I(0.70mV)/I(0.35mV) = 1200V (mV)
First epitaxial junctions with low subgap conductance
• Room temperature resistances very reproducible• Low temperature results of junctions:
![Page 20: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/20.jpg)
Bias coil
50 m
Qubit (70 m2) DC-SQUID
Flux-biased Phase Qubut with a single-crystal Al2O3Tunnel barrier
![Page 21: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/21.jpg)
Improvement of Junction Materials
T = 25 mK
Junction area 70 mm2
Amorphous barrier
![Page 22: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/22.jpg)
Improvement of Junction Materials
T = 25 mK
Junction area 70 mm2
Amorphous barrier
![Page 23: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/23.jpg)
Improvement of Junction Materials
T = 25 mK
Junction area 70 m2
Spectroscopy: Epitaxial Barrier
Splitting density reduced by ~ factor of 525 => ~5 /GHz
![Page 24: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/24.jpg)
Rabi oscillations from epi-qubits
• T*2 comparable to qubits of same design (max SiO2)
• Illustrates that the insulator is limiting decoherence source for this design
![Page 25: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/25.jpg)
Reduction of splitting density
• Interfacial effect• ~1 in 5 oxygens at Al interface• Agrees with reduced splitting
density
2 nm
epi-Re interface
non-epi Al interface
Oxygen0.43 nm
![Page 26: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/26.jpg)
Next year’s materials milestones
• Grow epi-top layers– Eliminate splittings?
• V/MgO junctions– Better lattice match– Lower temperatures– Lower barrier (thicker films)– Better manufacturability
• Integrate with min-SiO2 &vacuum crossover designs
3.03 Å
Vanadium MgO
4.13 Å
![Page 27: NIST ARDA/DTO review 2006 Materials David P. Pappas Seongshik Oh Jeffrey Kline](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d225503460f949f8352/html5/thumbnails/27.jpg)
Effect of Top electrodeThermally evaporated Al vs Sputtered Re
Base Epi Re Base Epi Re
Top AlTop Re
Note: In these samples, AlOx barriers are amorphous
AlOx
Base Re-AlOx
interface smooth
AlOx-Top Al interfacesmooth
AlOx-Top Re interfacerough
AlOx
Good I-V’s Bad I-V’s