Progress in Reactive Co-Evaporation on IBAD

Transcription

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. 1

2 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 2

3 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 lowcost materials: Coevaporation Simple and fast normal metal deposition 3

4 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 4

5 One Approach: RCE-CDR (Reactive Co- Evaporation by Cyclic Deposition and Reaction) Stability of YBCO in the p-t diagram Deposition rate d p ( 4Å) Average rate ORCE-CDR 2 pocket Pulsed deposition at low O 2 pressure followed by reaction in high O 2 Very high instantaneous deposition rates possible Lower average rate: required for kinetics of growth In situ growth 5

6 A Different Approach: Co-evaporation at low temperature followed by reaction at high T in O 2 2-step: Deposit precursor coating then process (ex situ) R. Hammond (Stanford U), D. Christen (ORNL), and J. Storer (LANL) studied this process ( ) Several deposition methods were used Liquid Precursor coating O 2 pocket was stable (no fluorine) deposited at low T and low O 2 (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 J c s were not consistent (some >3 MA/cm 2; others 1 MA/cm 2 ) TEM Section ORNL 6

7 An example of the 2-step process: Presently used by SuNAM in Korea SUNAM 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.) 7

8 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 lowcost materials: Coevaporation Simple and fast normal metal deposition 8

9 Solution Deposition Planarization (SDP) is a promising method for substrate finishing and eliminating defects 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 Y 2 O 3 bed layer FWHM MgO Texture ( ) Required RMS roughness in-plane alignment in MgO out-of-plane alignment in MgO RMS Roughness 5 x 5 m (nm) YBCO MgO Y 2 O 3 SDP TEM: Terry Holesinger Process developed by Los Alamos and Sandia National Laboratories For more details see LANL presentation in the Strategic Research session 9

10 Solution Deposition Planarization eliminates three steps in present CC manufacturing 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 Superconductor Superconductor IBAD Bed layer Barrier layer Polished, expensive metal substrate Current Manufacturing Process for HTS CC IBAD SDP Unpolished, inexpensive metal substrate Simplified SDP Process for HTS CC 10

11 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 11

12 In FY2010 introduced multiple-molarity coatings resulting in lowest roughnesses: less than 1 nm RMS 0.4 M coats 0.4 M 0.08 M Unpolished RMS (5x5 m): 26 nm SDP coatings (5x5 m): 0.5 nm R q (nm) M coats UNPOLISHED SUBSTRATE R q = 25.6 nm R a = 20.5 nm 1 SDP-coated SUBSTRATE R q = 0.56 nm R a = 0.45 nm Number of SDP coatings 12

13 High J c 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; J c not yet optimized MgO texture: = 4.6, = m YBCO film 4.1 MA/cm 2, LN2, sf 10 YBCO pole figure TEM Terry Holesinger = 2.4, = 0.9 J c (MAcm -2 ) H (T) YBCO Unpolished metal tape SDP Matias et al, Super. Sci. Tech., 23, (2010) Intensity Phi (degrees) 13

14 Best RCE Critical Current Results at LANL Best Self Field results to date: 3.0 MA/cm 2 in a 1.2 m film 2.5 MA/cm 2 in a 2.0 m film 950 A/cm-width in 6 m 4.1 MA/cm 2 in 1.0 m New result since PR09 PLD YBCO RCE-CDR On stainless substrate 1000 A/cm permanent magnets Measure full 1-cm width coated conductor in magnetic field Scale SF result from bridge 75.5 K YBCO thickness ( m) 14

15 HTS coatings on stainless steel substrates often exhibit delamination Stainless steel 316L substrates studied as a substrate for CC Have obtained some good (high I c ) 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 Thermal expansion (%) Hastelloy S316L YBCO reduced YBCO Delaminated YBCO/Ag coating Temperature ( C) > 0.5 % 15

16 Several approaches to obtain 1000 A/cm in Coated Conductors 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 J c in thicker films Demonstrated at LANL by PLD: 2 m, 5 MA/cm 2 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 LANL PLD results PR09 YBCO2 SDP/IBAD YBCO1 SDP/IBAD 1000 A/cm 2x 16

17 SDP allows for Stacked Coated Conductor layer structure with multiple SDP/IBAD/HTS layers J e in a Coated Conductor is dominated by the thickness of the substrate Thus, doubling I c effectively doubles J e 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 I c and J e several fold by using the same coating process used for one HTS layer repeatedly on the CC Of particular interest in applications requiring high J e YBCO SDP/IBAD METAL SUBSTRATE YBCO YBCO SDP/IBAD METAL TAPE YBCO YBCO 17

18 2-Layer HTS Stack preliminary result demonstrates feasibility: 700 A SDP1: 1 m YBCO1 by RCE: 2 m pole figure: = 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 = A/cm (SF measured directly) Total current 700 A More work is under way YBCO2 SDP/IBAD YBCO1 SDP/IBAD MgO2 =

19 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 J c 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 19

20 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 20

21 Plans for FY11 Optimize stack of YBCO layers for total I c > 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) One pass (two-step) process Furnace Potential for a high throughput, extremely high rate process 21

22 Summary LANL demonstrated 4.1 MA/cm 2, LN 2 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 22