D. E. Oates MIT Lincoln Laboratory, Lexington MA - PowerPoint Presentation

Slide1

D. E. OatesMIT Lincoln Laboratory, Lexington MAY. D. AgassiNaval Surface Warfare Center, Carderock Division, Bethesda MDB. H. Moeckly and C. YungSTI Inc. Santa Barbara, CAG. Carpenter and F. NiuSVT Associates, Eden Prairie, MN

MgB2 Thin Films on Metallic and Dielectric Substrates for Microwave Electronic and SRF applications

This work was sponsored by the Defense Threat Reduction Agency, the Office of Naval Research, and the Naval Surface Warfare Center,

Carderock

DivisionSlide2

Discovered to be superconducting in 2001 with a Tc = 39 KJ. Nagamatsu, N. Nakagawa, T. Muranaka, Y. Zenitani and J. Akimitsu,“Superconductivity at 39K in Magnesium Diboride,” Nature 410, 63 (2001)Believed to be BCS superconductorBulk and thin filmsNo isostructural compounds show high TcMgB2Slide3

OutlineIntroduction to MgB2 and MotivationFilm depositionMeasurements of surface impedancePhysics of MgB2 from microwave measurementsSummarySlide4

Motivation RF applications of MgB2 thin filmsTC = 40 KOperating T ≈ 20 KLow surface resistanceComparable to niobium at 4 KLong coherence length = 4 – 8 nmPolycrystalline films with good RF propertiesGrain boundaries are not weak linksHigh Critical FieldHc ≥ 1.5 TGood power handling

Crystal structureAlB2 (Hexagonal)Stable, stoichiometricSlide5

ApplicationsRF cavities coated with MgB2 for accelerator applicationsImprovement on niobium technologyFilms on metallic substratesHigh Q at high powerHC → RF breakdownPassive microwave electronicsFilms on dielectric substratesInexpensive polycrystalline substratesHigh Q at low to medium powerLow-loss delay lines – dispersive delay linesMiniature filtersIntermodulation distortion possible issueSlide6

OutlineIntroduction to MgB2 and MotivationFilm depositionMeasurements of surface impedancePhysics of MgB2 from microwave measurementsSummarySlide7

Advantages: Localized Source of High-Pressure Mg Vapor Different Mg and Substrate Temperatures

Films: T

C

 39K, T

C

 1K, Resistivity(

T

c

)  2

Ω

-cm

4” Wafers, scale

up possible

RMS roughness = 4.4 nm

Rotating blackbody heater

B. H. Moeckly et al., Supercond. Sci. Technol. 19, L21 (2006)

Solves MgB2 Film-growth Difficulties: Mg Volatility, Oxidation

Reactive Evaporation Film DepositionSlide8

MgB2 Thin-Film Properties500-nm MgB2 film on NbRMS surface roughness = 3.0 nmAFM surface scan

0.5-m film on sapphire40 >Tc > 39.5Low resistivitySharp transition Slide9

Joint Program with SVT AssociatesDeveloping ALD process and system for MgB2 depositionB2H6 and Mg(CpEt)2, or Mg(thd)2Plasma enhancedConformal coating methodNeeded for cavity coatingProgress to date: thin films of MgBxStill developing the process parameters

Atomic Layer Deposition of MgB2Slide10

OutlineIntroduction to MgB2 and MotivationFilm depositionMeasurements of surface impedanceSmall samples 1 cm x 1cm 2-inch diameter wafersPhysics of MgB2 from microwave measurementsSummarySlide11

Stripline Resonator for Measurements on Dielectric Substrates

Capacitive

coupling

Patterned

center line

Ground

planes

Used for measurement of

Z

S

(I

rf

,T, f),

intermodulation distortion, and 3

rd

harmonic generation.

Stripline

resonator

Input Spectrum

f

1

f

2

Frequency

Power

Output Spectrum

f

1

f

2

2f

1

-

f

2

2f

2

-

f

1

Resonator

f

1

f

2

+

Spectrum

Analyzer

IMD measurement

Output power (dBm)

Input power (dBm)

Fundamental

Intermod

150

mSlide12

Dielectric Resonator for Films on Metallic SubstratesCan be used with metallic or dielectric substratesDesigned for high-power measurementsFundamental frequency = 10.7 GHzTE011 modeSlide13

ResonatorsStripline vs. DielectricStripline Resonator: Side ViewConductor Cross Section

|J(x)/Jmax

|

Position from Center (

m)

J

max

~ 1.6 x 10

8

A/cm

2

150

m

m

rf

magnetic

field directions

Dielectric Resonator:

Top View

Position from Center (

mm)

|J(x)/

J

max

|

J

max

~ 4.0 x 10

6

A/cm

2

Cross

sectionSlide14

CW MeasurementSlide15

CW MeasurementFrequency (Hz)Insertion loss (dB)Data

FitSlide16

Time-Domain Pulsed TestsSlide17

Pulsed MeasurementSlide18

Low Power FitSlide19

Low-Power RS(T): MgB2 and NbRS extrapolated to 2.2 GHz by f 2

Niobium film on sapphirestripline

MgB

2

on

bulk

Nb

Dielectric resonator

MgB

2

on

sapphire

Stripline resonatorSlide20

RS vs HRF Dielectric and Metallic SubstratesDielectric res.Stripline res.

Stripline res.Slide21

Breakdown FieldsTMax PwrdBmQL (low pwr)Hrf max4.2

28.77.8x1062787.5

38.2

5.5x10

6

697

11

38.2

No breakdown

2.5x10

6

470

Max power available

MgB

2

on niobium substrateMeasured in dielectric resonator

Amplifier with +45 dBm output power recently installed

Breakdown most likely due to thermal effectsSlide22

PassivationSuccess at Film-StabilizationMgB2 Degrades in AirPassivation with 5 X (2.5 nm Al2O3 and 2.5 nm ZrO

2) by ALDOver 6 Months & 5 Temperature Cycles Rs Unchanged.

Q (f = 1. GHz)

 1. 10

8

(Measured in a 2” Dielectric Resonator.)

R

S

(1 GHz ) = 2 x 10

-7

ΩSlide23

OutlineIntroduction to MgB2 and MotivationFilm depositionMeasurements of surface impedancePhysics of MgB2 from microwave measurementsSummarySlide24

IMD and Rs vs Circulating PowerMgB2 ResonatorSimilar plot for XS

Circulating power (dBm)Surface resistance (Ω)

Normalized IMD (dBm)

Resonator

f

1

f

2

+

Spectrum

Analyzer

T = 20 K

T = 2.5 KSlide25

IMD vs T: MgB2 and YBCOYBCOt = 600 nmMgB

2 samplest = 150 nm

YBCO

→ d-wave order parameter →

1/T

2

at low

T

MgB

2

→ 6-fold symmetry →

1/T

2

at low

T

MgB

2

t = 500 nmSlide26

Order Parameter+-

-

ℓ = 2 Cuprates

ℓ = 6 MgB

2

+

-Slide27

SummaryMgB2 is promising for applicationsPolycrystalline films with good RF propertiesEpitaxy not needed Low surface resistance and good power handling on dielectric and metallic substratesMicrowave accelerator cavities – upgrade for niobium Remaining challengesDeposition on copperConformal coating method

Atomic layer deposition (ALD)Demonstrate Hrf > 2000 Oe

Electronics applications on inexpensive substrates

Slide28

Summary (Physics)Experimental evidence incompatible with s-wave symmetryTemperature dependence of intermodulation distortion (IMD)Increase of penetration depth at low temperaturesTheory based on extension of constitutive relation (London theory) and ℓ = 6 symmetry of order parameterNonlinear Meissner effect for IMDAndreev bound states for Dl(T)/l Conclusion: p gap has nodal order-parameter symmetry ℓ= 6

Implications for applicationsLinear low-T surface resistanceIntermodulation distortion greater than s-waveSlide29
Slide30

● Good fits with plausible parameters for all sapphire cuts and for LAOLow-T Penetration Depth and ℓ = 6 -Gap SymmetrySlide31

Nonlinear Meissner EffectResult of theory – nonlinear penetration depthIMD power

Temperature dependence at low temperature

For s-wave energy gap

For energy gap with nodes

For MgB

2,

hexagonal symmetry rules out d-wave

Best fit is with 6-fold symmetry

D. Agassi and D. E. Oates, PRB

72

, 014538 (2005), PRB

74

, 024517 (2006)

D. E. Oates, Y. D. Agassi and B. H.

Moeckly

, PRB

77

, 214521 (2008)

and

Physica

C 2012 in press

Intrinsic Nonlinearity: From Pair Breaking by the RF CurrentSlide32

Resistive TransitionSlide33

Long E-M Delay LinesYBCO on 5-cm diameter LaAlO3 44-ns delayInput

Output

G. C. Liang

et al

. Trans MTT vol. 44, 1289, (1996)

Replace YBCO

Inexpensive substrate

No epitaxy

Larger substrates for much longer

delays

500 ns possible

Also dispersive-delay lines