progress in reactive co-evaporation on ibad · 2011-04-27 · advanced cables and conductors...

Advanced Cables and Conductors Program Peer Review - June 30, 2010 - Alexandria, VA 1

Progress in Reactive Co-Evaporation on IBAD

Vladimir Matias, Yehyun Jung, Chris Sheehan

Superconductivity Technology Center

Los Alamos National Laboratory

LANL FY10 Funding: RCE R&D 2.1: $150K; 0.3 FTE

Project Goal: Explore processes and architectures to reduce cost and

improve performance of coated conductors

Our project addresses the OE HTS wire goals through significant

improvements in price performance ratio for HTS wire.


Superconducting power applications require low-cost HTS wire: $10/kA•m

Navigant Consulting market study (2006)

In the near-term, Navigant says cost of HTS wire is a barrier to commercialization of superconducting grid applications

For 2012 and beyond, Navigant study states DOE CC goals should be $10/kA•m, 77 K, SF, and $20/kA•m, 65 K, 2 T

These costs can only be achieved in large volume: > 10,000 km/yr

We need processes that can deposit > 2 tons of YBCO per year or ~ 1 kg per hour efficiently and produce high performance HTS coatings


A complete low-cost CC manufacturing strategy is required

Inexpensive substrate: stainless steel

with low-cost finish

Universal and inexpensive finishing process: SDP

Low-cost template formation process: fast IBAD

Simple buffer layer architecture: single

textured layer

Fast, large-area and high-quality HTS deposition process with low-cost materials: Coevaporation

Simple and fast normal metal deposition


A process to transfer HTS materials efficiently at high rate needed: Co-evaporation

Co-evaporation of individual elements

Elemental sources inherently least expensive

Very high deposition rate can be used

Multi-hundred kW systems evaporating kg/hr exist in industry

Scalable to large deposition area

Thick film potential

Yttrium Barium Copper

Y Ba Cu


One Approach: RCE-CDR (Reactive Co-Evaporation by Cyclic Deposition and Reaction)

Stability of YBCO in the p-T diagram

O2 pocket

Deposition rate

dp ( 4Å)

Average rate

RCE-CDR

Pulsed deposition at low O2 pressure followed by reaction in high O2

Very high instantaneous deposition rates possible

Lower average rate: required for kinetics of growth

In situ growth


A Different Approach: Co-evaporation at low temperature followed by reaction at high T in O2

O2 pocket

2-step: Deposit precursor coating then process (ex situ)

R. Hammond (Stanford U), D. Christen (ORNL), and J. Storer (LANL) studied this process (2001-2006)

Several deposition methods were used

Precursor coating was stable (no fluorine) – deposited at low T and low O2 (glassy phase)

Liquid-assisted growth at high T

Very fast reaction and growth rate (>1000 Å/s)

Pinning centers hard to add; nearly defect-free

Jc’s were not consistent (some >3 MA/cm2; others 1 MA/cm2)

Liquid

TEM Section ORNL


Use IBAD-MgO templates (SuNAM fabricates templates up to 2 km in length)

SuNAM HTS growth process is fast ( 1 minute)

RCE-DR

Large deposition area

Large process margin

Typical > 250 A/cm, max ~ 500 A/cm (1.1 m)

0.6 m thick film ~ 600 m/hr.,

1.5 m thick film ~ 300 m/hr. (4 mm width equiv.)

SUNAM

An example of the 2-step process: Presently used by SuNAM in Korea


A complete low-cost CC manufacturing strategy is required

Inexpensive substrate: stainless steel

with low-cost finish

Universal and inexpensive finishing process: SDP

Low-cost template formation process: fast IBAD

Simple buffer layer architecture: single

textured layer

Fast, large-area and high-quality HTS deposition process with low-cost materials: Coevaporation

Simple and fast normal metal deposition


Solution Deposition Planarization (SDP) is a promising method for substrate finishing and eliminating defects

For more details see LANL presentation in the Strategic Research session

TEM: Terry Holesinger

Y2O3 SDP

MgO

YBCO

IBAD-MgO is extremely fast, but needs an inexpensive and fast process to produce smooth substrates for IBAD

Solution deposited layer encapsulates metal tape (prevents metal interdiffusion) and smooths out the surface

After solution deposition the substrate is IBAD-ready with an Y2O3 bed layer

Process developed by Los Alamos and Sandia National Laboratories

0

2

4

6

8

10

12

0 2 4 6 8 10

FW

HM

Mg

O T

ext

ure

(°)

RMS Roughness 5 x 5 m (nm)

in-plane alignment in MgO

out-of-plane alignment in MgO

Required RMS roughness


Solution Deposition Planarization eliminates three steps in present CC manufacturing

Current Manufacturing Process for HTS CC

Simplified SDP Process for HTS CC

Polished, expensive metal substrate

Superconductor

Barrier layer

Bed layer

IBAD

Superconductor

SDP

IBAD

SDP combines electropolishing, barrier and bed layer deposition

into one process step for IBAD CC

Additionally it broadens the range of substrates that can be used

Unpolished, inexpensive metal substrate


In FY2010 LANL built a scaled-up system for SDP

New deposition system allows for longer and wider tape coating

Previous system only allowed 3 meter coatings

New system capable of coating 100 meter lengths

Higher throughput by doing three SDP coatings in series, as well as 10-cm wide tape

Significant improvements included in the design of the new system:

Continuous flow of solution with filtering

In-line tape cleaning

Laminar air flow

Automated process control

Materials to be provided to our industrial partners

NEW SYSTEM


In FY2010 introduced multiple-molarity coatings resulting in lowest roughnesses: less than 1 nm RMS

Unpolished RMS (5x5 m): 26 nm

15-20 SDP coatings (5x5 m): 0.5 nm

Rq = 0.56 nm Ra = 0.45 nm

Rq = 25.6 nm Ra = 20.5 nm

UNPOLISHED SUBSTRATE

1

10

0 5 10 15 20 25 30

0.4 M

0.08 M

Rq (

nm

)

Number of SDP coatings

0.4 M coats

0.08 M coats

SDP-coated SUBSTRATE


High Jc achieved by Reactive Co-Evaporation on SDP-prepared substrate

YBCO deposited by LANL RCE on MgO template grown on SDP Y-Al-O

Simplified buffer structure

YBCO deposited on 30 nm MgO; Jc not yet optimized

MgO texture: = 4.6°, = 1.5°

1.0 m YBCO film

-50 0 50 100 150 200 250 300 350

Inte

nsity

Phi (degrees)

YBCO pole figure 4.1 MA/cm2, LN2, sf = 2.4°, = 0.9°

YBCO

Unpolished metal tape

SDP

Matias et al, Super. Sci. Tech., 23, 014018 (2010)

TEM Terry Holesinger

0H (T)

1

10

Jc (

MA

cm-2

)

0.1


Best RCE Critical Current Results at LANL

permanent magnets

• Best Self Field results to date:

– 3.0 MA/cm2 in a 1.2 m film

– 2.5 MA/cm2 in a 2.0 m film

– 950 A/cm-width in 6 m

– 4.1 MA/cm2 in 1.0 m 1000 A/cm

PLD YBCO

75.5 K

YBCO thickness ( m)

RCE-CDR

New result since PR09

• Measure full 1-cm width coated conductor in magnetic field

• Scale SF result from bridge

On stainless substrate


0

0.5

1

1.5

2

0 200 400 600 800 1000

HastelloyS316LYBCOreduced YBCO

Therm

al e

xpansi

on (

%)

Temperature (°C)

HTS coatings on stainless steel substrates often exhibit delamination

Stainless steel 316L substrates studied as a substrate for CC

Have obtained some good (high Ic) results

Very often, however, the YBCO films delaminate

Proposed mechanism is buckling-driven delamination under compressive stress from thermal expansion differences between S316L and YBCO

Delaminated YBCO/Ag coating

> 0.5 %


Several approaches to obtain 1000 A/cm in Coated Conductors

1000 A/cm

LANL PLD results PR09

Conventional approach is to attain higher currents by making thicker films: 5–10 m HTS films have been shown by several methods to yield close to 1000 A/cm

A harder way is to increase Jc in thicker films

Demonstrated at LANL by PLD: 2 m, 5 MA/cm2

Not easy; perhaps also not practical in manufacturing

A third way is to double the 500 A/cm film

Much easier to achieve 500 A/cm in 2-3 m

Reset the crystalline structure with a second IBAD layer and then grow a second HTS layer

SDP/IBAD YBCO1

YBCO2

SDP/IBAD

2x


YBCO

YBCO

SDP allows for ‘Stacked’ Coated Conductor layer structure with multiple SDP/IBAD/HTS layers

Je in a Coated Conductor is dominated

by the thickness of the substrate

Thus, doubling Ic effectively doubles Je

SDP enables one to grow a second

YBCO layer on top of a YBCO layer

SDP allows for stacks of HTS layers on

both sides of the metal tape

Can increase Ic and Je several fold by

using the same coating process used

for one HTS layer repeatedly on the CC

Of particular interest in applications

requiring high Je

METAL TAPE

SDP/IBAD YBCO

YBCO

YBCO SDP/IBAD

METAL SUBSTRATE


2-Layer HTS Stack preliminary result demonstrates feasibility: 700 A

SDP1: 1 m

YBCO1 by RCE: 2 m

pole figure: =2.7°

540 A/cm (SF value extrapolated from magnetic field measurement)

Ag/YBCO surface > 100 nm RMS roughness

SDP2: 1 m, RMS 2 nm

IBAD MgO2 deposited

pole figure =7.9°

YBCO2 by RCE: 2 m

pole figure =4.9°

185 A/cm (SF measured directly)

Total current 700 A

More work is under way

YBCO2

SDP/IBAD YBCO1

SDP/IBAD

MgO2 = 7.9°


Milestones – RCE Research (Task 1.3)

Demonstrate 1000 A/cm-width performance in self field at LN2 (July 31, 2010) o Previously demonstrated 950 A/cm (6 m); so far not successful in 4 m

o Demonstrated > 400 A/cm in a 1.0 m film

o Using a two-layer SDP/IBAD stack approach, thus far: ~700 A in 4 m of YBCO

Demonstrate high Jc RBCO at an instantaneous rate of 150 Å/s

o demonstrated at up to 80 Å/s

o milestone readjusted as 80 Å/s is deemed sufficient for RCE-CDR


Technology transfer, collaborations and partnerships

Close collaboration, a number of visits and sample exchanges between LANL and Sandia on the SDP process

Numerous discussions with R. Hammond (Stanford University) regarding HTS deposition

Joint LANL/SNL R&D 100 Award Entry for SDP process

2 conference presentations (one invited talk) and 1 journal article

SDP system

R&D100


Plans for FY11

Optimize stack of YBCO layers for total Ic > 1000 A; coat both sides of substrate and several layers per side

LANL plans ot work with Stanford to explore new routes to low-cost coevaporation – (revisiting Hammond’s Path B)

Furnace

Potential for a high throughput, extremely high rate process

One pass (two-step) process


Summary

LANL demonstrated 4.1 MA/cm2, LN2 SF, in 1 m film on IBAD template by RCE-CDR

LANL introduced a new architecture using stacks of SDP/IBAD/HTS layers; first result appears promising: 700 A/cm

LANL proposes revisiting research on the 2-step co-evaporation process as a viable route to low-cost CC manufacturing

progress in reactive co-evaporation on ibad · 2011-04-27 · advanced cables and conductors...

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