(12) United States Patent (10) Patent N0.: US 7,736,761 B2 Foltyn Et A1

US007736761B2

(12) United States Patent (10) Patent N0.: US 7,736,761 B2 Foltyn et a1. (45) Date of Patent: Jun. 15, 2010

(54) BUFFER LAYER FOR THIN FILM (58) Field of Classi?cation Search ...... 505/230, STRUCTURES 505/237, 238; 428/699i702, 930; 174/1251; 427/62 (75) Inventors: Stephen R. Foltyn, Los Alamos, NM See application ?le for complete search history. (US); Quanxi Jia, Los Alamos, NM (56) References Cited (US); Paul N. Arendt, Los Alamos, NM (US); Haiyan Wang, Los Alamos, NM U.S. PATENT DOCUMENTS (Us) 6,410,487 B1 * 6/2002 Miller et a1...... 505/239 6,716,545 B1 * 4/2004 Holesinger et a1. 428/701 (73) Assignee: Los Alamos National Security, LLC, 6,756,139 B2 * 6/2004 Jia et a1...... 428/701 Los Alamos, NM (US) 6,800,591 B2 * 10/2004 Jia et a1...... 505/237 6,921,741 B2 * 7/2005 Arendt et a1...... 505/239 Notice: Subject to any disclaimer, the term of this FOREIGN PATENT DOCUMENTS patent is extended or adjusted under 35 WO 03/021656 * 3/2003 U.S.C. 154(b) by 182 days. * cited by examiner (21) Appl. No.: 11/591,269 Primary ExamineriSteven Bos Assistant ExamineriPaul A WartaloWicZ (22) Filed: Oct. 31, 2006 (74) Attorney, Agent, or FirmiBruce H. Cottrell; Juliet A. Jones (65) Prior Publication Data US 2010/0093547 A1 Apr. 15, 2010 (57) ABSTRACT A composite structure including a base substrate and a layer Related US. Application Data of a mixture of strontium titanate and strontium ruthenate is (62) Division of application No. 10/624,855, ?led on Jul. provided. A superconducting article can include a composite 21, 2003, noW Pat. No. 7,129,196. structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium (51) Int. Cl. titanate and strontium ruthenate and a top-layer of a super B32B 9/00 (2006.01) conducting material such as YBCO upon the buffer layer. (52) US. Cl...... 428/701; 428/702; 428/930; 505/237; 505/238; 174/125.1 12 Claims, 2 Drawing Sheets

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0mm N ‘- ‘D. O (ZLUOIVW) Mgsuap wanna wonyg US 7,736,761 B2 1 2 BUFFER LAYER FOR THIN FILM Wherein strontium titanate is suggested as a buffer layer hav STRUCTURES ing a moderate dielectric constant. Despite the many prior uses of both stronium ruthenate and RELATED APPLICATIONS stronium titanate, the use of stronium titanate alone or the use of a mixture of stronium ruthenate and stronium titanate as a This application is a divisional of patent application Ser. buffer layer has not been previously described upon an IBAD No. 10/624,855 ?led, Jul. 21, 2003 now US. Pat. No. 7,129, magnesium oxide layer in a coated conductor superconduct 196 issued Oct. 31, 2006. ing structure. Additionally, the use of a mixture of stronium ruthenate and stronium titanate as a buffer layer has not been STATEMENT REGARDING FEDERAL RIGHTS previously described as a layer in other electronic applica tions such as ferroelectric, ferromagnetic, piezoelectric and This invention Was made With government support under the like. Contract No. DE-AC52-06NA25396 aWarded by the US. It is an object of the present invention to provide composite Department of Energy. The government has certain rights in structures including a buffer layer of strontium titanate or a the invention. mixture of strontium titanate and strontium ruthenate (SrTixRul_xO3 Where 0oxides, ferroelectric, ferromagnetic, pieZoelectric, layer of magnesium oxide thereon, and a buffer layer of insulating, and semiconductive materials are desired in the SrTi,€Ru1_,€O3 Where 0strontium oxide, Zirconium substrate is a polycrystalline metal as these materials are oxide, barium oxide, europium oxide, samarium oxide and generally ?exible, i.e., they can be shaped. For other applica other materials such as described in US. Pat. No. 6,190,752 tions, the base substrate on Which other oriented materials are by Do et al. Preferably, the layer of oriented cubic oxide material having a rock-salt-like structure is a magnesium deposited may be polycrystalline ceramics, either ?exible or 40 non-?exible. For still other applications, the base substrate oxide layer. Such a MgO layer is preferably deposited by may be a single crystal substrate such as magnesium oxide, electron beam evaporation With an ion beam assist. The MgO lanthanum aluminate, or aluminum oxide. layer in the ion-beam-assisted deposition is typically sput Some base substrates can include a layer of a metal oxide or tered from a magnesiun oxide target. An ion-assisted, elec tron-beam evaporation system similar to that described by metal oxynitride material deposited upon an underlying sub 45 strate material. Such layers can be crystalline or amorphous. Wang et al., App. Phys. Lett., vol. 71, no. 20, pp. 2955-2957 By “crystalline” is meant that the atoms of the material have (1997), can be used to deposit such a MgO ?lm. Alternatively, order over various length scales of longer than a feW nanom a dual-ion-beam sputtering system similar to that described eters. By “order” is meant that the atoms have a de?nite by Iijima et al., IEEE Trans. Appl. Super., vol. 3, no. 1, pp. 1510 (1993), can be used to deposit such a MgO ?lm. Gen pattern referred to as a lattice structure. 50 erally, the substrate normal to ion-assist beam angle is 45:3°. In some instances, the base substrate can include an ori ented cubic oxide layer of, e.g., MgO, preferably deposited by An additional thin homo-epitaxial layer of MgO can be ion-beam-assisted deposition (IBAD) over one or more optionally deposited as a layer on some base substrates, espe underlying materials. For example, a metal oxide or metal cially those including an IBAD layer of magnesium oxide. oxynitride material layer can be deposited on an underlying 55 Such an additional thin homo-epitaxial layer of MgO can be material including a nickel based alloy coated With a ?rst deposited by a process such as electron beam or magnetron layer of aluminum oxide and a next layer of yttrium oxide, the sputter deposition. This thin homo-epitaxial layer can gener depositions carried out by pulsed laser deposition, e-beam ally be about 50 angstroms to 1000 angstroms, prefereably evaporation, sputtering or by any other suitable means. Such 100 angstroms to 500 angstroms in thickness. a metal oxide or metal oxynitride material layer is generally 60 As some base substrates can have a rough surface, such deposited at temperatures of generally about 100° C. Such a surfaces can be mechanically polished, electrochemically metal oxide or metal oxynitride material layer is typically polished or chemically mechanically polished to provide a from about 50 angstroms to about 1000 angstroms in thick smoother surface for optimization of properties in subse ness, preferably from about 50 angstroms to about 200 ang quently deposited layers. Electrochemical polishing of metal stroms. Among the metal oxide or metal oxynitride materials 65 lic substrates in an acid bath as described by Kreiskott et al., suitable as the layer are included yttrium oxide (Y2O3), alu Supercond. Sci. Technol., vol. 16, pp. 613-616 (2003), is minum oxynitride (AlON), erbium oxide (Er2O3), yttria-sta generally preferred. US 7,736,761 B2 5 6 In one embodiment of the present invention, the high tem ness. These buffer layers are generally deposited at tempera perature superconducting (HTS) material is generallyYBCO, tures of greater than about 600° C., preferably at temperatures e.g., YBa2Cu3O7_6, Y2Ba4Cu7O14H, or YBa2Cu4O8, of from about 650° C. to about 850° C. For SrTi,CRul_,€O3 although other minor variations of this basic superconducting Where x:1, deposition temperatures of betWeen about 800° C. material, such as use of other rare earth metals as a substitute and 825° C. have been found preferably for a base metallic for some or all of the yttrium, may also be used. A mixture of substrate including a magnesium oxide layer deposited by the rare earth metal europium With yttrium may be one pre IBAD thereon. ferred combination. Other superconducting materials such as In pulsed laser deposition, poWder of the material to be bismuth and thallium based superconductor materials may deposited can be initially pressed into a disk or pellet under also be employed. YBa2Cu3O7_6 is generally preferred as the high pressure, generally above about 1000 pounds per square superconducting material. inch (PSI) and the pressed disk then sintered in an oxygen A high temperature superconducting (HTS) layer, e.g., a atmosphere or an oxygen-containing atmosphere at tempera YBCO layer, can be deposited, e.g., by pulsed laser deposi tures of about 950° C. for at least about 1 hour, preferably tion or by methods such as evaporation including coevapora from about 12 to about 24 hours. An apparatus suitable for tion, e-beam evaporation and activated reactive evaporation, pulsed laser deposition is shoWn in Appl. Phys. Lett. 56, 578 sputtering including magnetron sputtering, ion beam sputter (1990), “Effects of Beam Parameters on Excimer Laser ing and ion assisted sputtering, cathodic arc deposition, Deposition of YBa2Cu3O7_6”, such description hereby incor chemical vapor deposition, organometallic chemical vapor porated by reference. deposition, plasma enhanced chemical vapor deposition, Suitable conditions for pulsed laser deposition include, molecular beam epitaxy, a sol-gel process, liquid phase epi 20 e.g., the laser, such as an excimer laser (20 nanoseconds (ns), taxy and the like. 248 or 308 nanometers (nm)), targeted upon a rotating pellet The composite structure provided in accordance With the of the target material at an incident angle of about 45°. The present invention includes a base substrate and a layer of a substrate can be mounted upon a heated holder rotated at mixture of strontium titanate and strontium ruthenate. Such a about 0.5 rpm to minimiZe thickness variations in the result composite structure is useful for subsequent deposition of 25 ant ?lm or coating, The substrate can be heated during depo thin ?lm layers of, e.g., YBCO. Optionally, other thin ?lms sition at temperatures from about 600° C. to about 950° C., can be deposited from a material selected from the group preferably from about 700° C. to about 850° C. An oxygen consisting of superconductors, including high temperature atmosphere of from about 0.1 millitorr (mTorr) to about 500 superconductors, semiconductors, photovoltaic materials, mTorr, preferably from about 100 mTorr to about 400 mTorr, magnetic materials, ferroelectric materials, ferromagnetic 30 can be maintained Within the deposition chamber during the materials, pieZoelectric materials, insulating materials, con deposition. Distance betWeen the substrate and the pellet can ductive materials and precursors of superconductors or high be from about 4 centimeters (cm) to about 10 cm. temperature superconductors. The composite structure is The deposition rate of the ?lm can be varied from about 0.1 especially preferred for subsequent deposition of high tem angstroms per second (A/ s) to about 200 A/ s by changing the perature superconductor materials. 35 laser repetition rate from about 0.1 hertZ (HZ) to about 200 Optionally Within the present invention, one or more buffer HZ. Generally, the laser beam can have dimensions of about 3 layers can be deposited so that they are betWeen the compos millimeters (mm) by 4 mm With an average energy density of ite structure (i.e., the base substrate and the layer of a mixture from about 1 to 4 joules per square centimeter (J/cm2). After of strontium titanate and strontium ruthenate) and any sub se deposition, the ?lms generally are cooled Within an oxygen quent high temperature superconducting layer such as 40 atmosphere of greater than about 100 Torr to room tempera YBCO. The buffer layers can provide assistance in lattice ture. matching. Such so-called “buffer layers” should have good Finally, Where a subsequent layer of YBCO is deposited, it “structural compatibility” betWeen the layer of strontium can generally be deposited by pulsed laser deposition at a titanate or the layer of a mixture of strontium titanate and thickness of, e.g., about 10,000 angstroms to 20,000 ang strontium ruthenate and subsequently deposited supercon 45 stroms. ducting materials, e.g., YBCO, and should have good chemi The present invention is more particularly described in the cal compatibility With adjacent layers. By “chemical compat folloWing examples Which are intended as illustrative only, ibility” is meant that the buffer layer does not undergo since numerous modi?cations and variations Will be apparent property-degrading chemical interactions, or has minimal to those skilled in the art. interactions if at all, With the adjacent layers. By “structural 50 compatibility” is meant that the buffer layer has a substan EXAMPLE 1 tially similar lattice structure With any subsequently depos ited material, e.g., superconductive material. A nickel alloy substrate (Hastelloy C276) Was ultrasoni In one embodiment of the present invention, Where the base cally cleaned in soap and Water, rinsed With deioniZed Water, substrate includes a magnesium oxide layer thereon, prefer 55 rinsed With methanol and bloWn dry With ?ltered nitrogen. A ably such a magnesium oxide layer deposited by IBAD, the layer of aluminum oxide about 350 angstroms in thickness buffer layer is SrTi,€Ru1_,€O3 Where 0<10_6 temperature in the range of about 800° C. to about 8250 C. Torr With a total pressure during deposition of about 1><10_4 Although the present invention has been described With Torr The electron gun heated the MgO source to maintain a reference to speci?c details, it is not intended that such details deposition rate of about 0. 1 5 nm/ sec. The ion-assist gun volt should be regarded as limitations upon the scope of the inven age and current density Were about 750 eV and 100 uA/cm2 tion, except as and to the extent that they are included in the respectively. accompanying claims. Onto this resultant article Was deposited a layer of MgO What is claimed is: about 125 angstroms in thickness using ion beam assisted 1. A composite structure for subsequent groWth of an epi electron beam deposition With an ion assist gas of argon. Onto taxial ?lm layer thereon comprising: the lBAD-MgO layer Was then deposited a layer of homoepi a base substrate; and, taxial MgO (about 300 angstroms in thickness) by magnetron a buffer layer of a single phase SrTi,€Ru1_,€O3 Where 0<106 A/cm2 using a standard four-point polycrystalline metals, polycrystalline ceramics, single crys measurement. The projected 1c is 320 Amperes across a 20 tal lanthanum aluminum oxide, single crystal aluminum sample 1 cm Wide. oxide, single crystal magnesium oxide, silica and glass. 4. The composite structure of claim 1 Wherein said base EXAMPLE 2 substrate is of a material selected from the group consisting of polycrystalline ceramics, single crystal lanthanum aluminum Additional nickel alloy substrates having similar coatings 25 oxide, single crystal aluminum oxide, single crystal magne of aluminum oxide, yttrium oxide and magnesium oxide sium oxide, silica and glass. thereon Were coated in the manner of Example 1 With various 5. The composite structure of claim 1 Where x:0.5. ratios of SrTi,CRul_,€O3 Where 0