Deposition and patterning of YBaCuO superconducting thin films by sequentialmultilayer depositionFrancine C. Case Citation: Journal of Applied Physics 67, 4365 (1990); doi: 10.1063/1.344929 View online: http://dx.doi.org/10.1063/1.344929 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/67/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Superconducting thin films of YBaCuO prepared by metalorganic chemical vapor deposition J. Appl. Phys. 67, 1562 (1990); 10.1063/1.345666 Preparation of superconducting Y–Ba–Cu–O thin films J. Vac. Sci. Technol. A 7, 3147 (1989); 10.1116/1.576329 Deposition and annealing of ion beam sputtered YBaCuO superconducting films Appl. Phys. Lett. 55, 501 (1989); 10.1063/1.102430 Sequentially evaporated thin YBaCuO superconductor films: Composition and processing effects AIP Conf. Proc. 182, 147 (1989); 10.1063/1.37945 Preparation and patterning of YBaCuO thin films obtained by sequential deposition of CuO x /Y2O3/BaF2 Appl. Phys. Lett. 53, 698 (1988); 10.1063/1.100644

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fluence of 1011 cm -2. Therefore, the linear dimension sensi­tivity ofRS is about a factor of 10 less than TEM.

In conclusion we have made a comparative study of po­lish-induced damage in (100) Si GaAs by RS and TEM. We have found that the depth dependence of the dislocation den­sity follows the same exponential depth dependence as the polish-induced strain. The polish time behavior of both types of polish-induced effects can be accounted for on the basis of a one-dimensional diffusion model. However, the skin depth of the dislocation density, as determined by TEM, is a factor of 10 greater than the strain skin-depth (RS). This observa­tion of different relative sensitivities of these two methods is confirmed by a study of GaAs with known dislocation densi­ties and is consistent with previous results. This investiga­tion demonstrates the value of such comparative experi­ments in order to fully understand this important process.

The authors wish to thank J. Jayakody for performing the Raman measurements on the GaAs/Si samples. Use of

the electron microscopes at the National Center for Electron Microscopy of Lawrence Berkely Laboratory is acknowl­edged. The Berkeley part of this work was supported by the Materials Science Division of the U.S. Department of Ener­gy under Contract No. DEAC03-76SFOOO98. F.H.P. ac­knowledges the support of the Army Research Office, Con­tract No. DAAG29-85-K-0076.

IZ. Hang, H. Shen, and F. Pollak, J. App!. Phys. 64,3233 ( 1988) and refer­ences therein.

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4G. Burns, F. H. Dacol, C. R. Wie, E. Burstein, and M. Cardona. Solid State Commun. 39, 1137 ( 1987).

Deposition and patterning of Y-Ba-Cu-O superconducting thin films by sequential multilayer deposition

Francine C_ Case LTV Missiles and Electronics Group, P. 0. Box 650003, Dallas, Texas 75265-0003

(Received 6 November 1989; accepted for publication l3 January 1990)

Y-Ba-Cu-O superconducting thin films on 100 and 110 SrTiO, were deposited under identical conditions by annealing thick layers of sequentially e-beam evaporated Cu, Y, and BaF 2' A comparison of these films is presented. Using a variation on the same technique, a 135-,um­wide superconducting strip was deposited on 100 SrTi01 by patterning of the first layer (copper) in the multilayer stack. Resistance data for this sample are presented. Superconducting dipoles (50 X 850,um) were also patterned on yttria-stabilized Zr02 by this same technique.

Thin films of superconducting Y-Ba-Cu-O have been prepared by many techniques including ion-beam sputter­ing, I chemical vapor deposition, 2 molecular-beam epitaxy, 3

laser evaporation,4 and electron-beam co-evaporation. 5 Se­quential multilayer deposition, followed by high-tempera­ture annealing in flowing oxygen, can provide improved re­producibility over that of the co-evaporation method. (, This generally entails deposition of multipie sets of three sequen­tially layered Cu-, Y -, and Ba-containing compounds. 7.8 Re­sults of this layering method using only one set of three thick component films is discussed for Y -Ba-Cu-O on 100 and 110 SrTi03 substrates.

Patterned superconducting films have many potential applications in the fields of optics and electronics, and suc­cessful deposition of stable superconducting structures is an area of intense activity. Several patterning techniques have been reported. For example, a focused 20-keV Ga ion beam has been used to pattern submicrometer bridge structures.9

Successful deposition of a 6OO-,um-wide superconducting

strip by patterning the copper layer, prior to oxidation, fol­lowed by Y 20, and BaF2 depositions, has been reported 10;

however, no resistivity data were avaiiable for these struc­tures.

l.nthis work, a comparison is made between Y -Ba-Cu-O thin films Simultaneously deposited by the sequential multi­layering technique onto 100and 110 SrTiO,. The patterning procedure and results for a 13S-pm-wide superconducting strip on 100 SrTi03 is also repOrted, along with evidence of successful patterning of dipole structures on yttria-stabilized Zr02 •

Two-square SrTi03 (100)- and (llO)-oriented sub­strates, 6 mm on a side, were bonded to the center of a l-in.­diam silicon wafer and loaded into an Edwards electron­beam deposition system. Single iayerR of cOQQec yttrium_

and barium fluoride, approximately 1300, 1200, and 4400 A, respectively, were sequentially e-beam evaporated at a tem­perature of 600 0c. The entire film structure consisted of only one set of three layers. The samples were then annealed

4365 J. Appl. Phys. 67 (9), 1 May 1990 0021-8979/90/094365-03$03.00 © 1 990 American Institute of Physics 4365

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" '-, I

1 :

I I I I I I I I

~=l //// l ~-b ,d 1

, '- a

I L .. ~_JI __ -LI __ -LI __ ..J

',0 100 150 200 250 300

TEMPERATURE K)

FIG, I. The temperature dependence of resistance for Y -8a-Cu-O super­conductlllg thlll films deposited under identical colldillllllS on lal 100 and (h) 110 SrTiO, suhqr:ltes and repeated on 100 SrTiO, I c) fin: weeks and

(t!) fi\t~ lll(lIlths later.

near 820 ·C in a tube furnace in flowing oxygen for 4 h, fol­lowed by a 1 !-h cooldown. The final film thicknesses were approximately 1 flll1.

Figures 1 (a) and 1 (b) show the temperature depen­dence of resistivity for the two samples on 100 and 110 orien­tations. respectively. For the 100 orientation T:""cl = 93 K with T, = 89 K, whereas T:""d = 84 K with T, = 64 K for the film on 110 SrTiO,. This behavior is opposite to that cited for Y-Ba-Cu-O films on the substrate orientations in Ref. 11. At 77 and 14 K. J, is 2.4 X IOJ and 1.2 X 104 A/cm2

,

respectively. for the film on 100 SrTiO,. After five weeks, this film was remeasured and found to have increased in resistance slightly in the temperature range from 300·C to near T:,n,,"; however, no significant change is observed in the transition region. See Fig. 1 (c). Also shown in Fig. 1 (d) is the data for the same film five months later. X-ray data indi-

1 ~m

FIG. 2. SEM comparison of the grain structures for Y -Ba-Cu-O supercon­dueling thin-film strip and adjacent insulating Y -Ba-O.

4366 J. Appl. Phys" Vol. 67, NO.9, 1 May 1990

FIG. 3. The temperature dependence of resistance for the US-plll-widt' Y -Ba-Cu-O superconducting thin-film strip on 100 SrTiO"

cate c-axis orientation normal to the substrate plane for the film on 100 SrTiO,; whereas random orientation is observed for the film on 110 SrTiOJ •

A copper layer was deposited at 75 ·C onto a 100 SrTiO, substrate upon which was patterned a 135-flm-wide strip in an AZ5214E photoresist. Following photoresist liftoff, the SrTiO, with the patterned copper strip was remounted into the deposition system, and the next two layers in the film stack (yttrium and barium fluoride) were deposited at 75°C.

This sample was then annealed in flowing oxygen at 820 ·C, resulting in a 13S-flm-wide Y -Ba-Cu-O supercon­ducting strip immersed in an insulating Y-Ba-O back­ground. Figure 2 is a scanning electron micrograph (SEM) of this strip, which contrasts the adjacent Y-8a-Cu-O and Y -Ba-O regions of the sample. Figure 3 is a plot of the tem-

H Imm

FIG. 4. Patterned Y -Ba-Cu-O superconducting dipole structures (50)< 850 11m) on yttria-stabilized ZrO,.

Francine C, Case 4366

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perature dependence of resistance for the superconducting strip. The room-temperature resistivity is 1.9:' mn cm and Tc = 86 K. The low substrate temperature on SrTiO} was used for deposition of the patterned structures only and was necessitated by the temperature limits imposed by the photo­resist. Clearly, the resistive response of the 135-/lm-wide pat­terned superconducting strip in Fig. 3 is quite respectable. The limited size of this structure, immersed in an insulating matrix, precludes a meaningful comparison of growth prop­erties between this patterned strip deposited at 75°C and the full coverage films deposited at 600 °C represented in Fig. 1. A comparison of growth properties at these two different deposition temperatures was not the intent of this communi­cation. In both cases, we rely on high temperature annealing to both mix and oxygenate these multilayers.

This same technique for patterning superconducting structures was then used to deposit superconducting dipoles (50/lm wide X 850 /lm long) on a l-in.-diam yttria-stabi­lized zr02 substrate. Figure 4 is an optical photo showing these completed Y-Ba-Cu-O dipole structures. The mini­mum linewidth capability is to be determined; however there appears to be no a priori reason why the linewidth limit should not be similar to that imposed by standard lithogra­phic procedures on the copper layer itself. Again, no growth diagnostics were performed on these patterned structures so orientation is not known.

The author would like to acknowledge H. E. Ratzlafffor his technical assistance with all aspects of this work, W. A. Patey for film deposition, J. S. Smotherman for photolithog­raphy and T. A. Shafer for x-ray diffractometry. Also appre­ciated are helpful discussions with colleagues M. E. Koch, A. J. Brouns, and W. E. Case.

I A. 1. Kingdon. O. Auciello, M. S. Ameen, and S. H. Rou, App\. Phys. Lett. 55, 301 (1989).

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Superconducting melt-textured thin films prepared by a spray pyrolysis method

E. Ban and Y. Matsuoka Department of Physics, Meijo University, Tenpaku-ku, Nagoya 468, Japan

H. Ogawa Department of Transport Machine Engineering, Meijo University. Tenpaku-ku. Nagoya 468. Japan

(Received 28 September 1989; accepted for publication 8 January 1990)

YBa2Cu307_x thin films were prepared on (lOO)yttria-stabilized zirconia (YSZ) by a spray pyrolysis method. The films were fired rapidly at l000-1020°C in flowing helium atmosphere and then annealed in oxygen, These melt-textured thin films had the aligned grain structure consisting of large, platelike grains over a wide area. The films thus formed showed relatively high critical current density Jc more than 4000 A/cm2

, and the best J.: of the film fired at 1010 °C was 4800 A/cm! at 77 K in zero magnetic field. The melt-textured growth processing was found to be more useful for the enhancement of the J, value of thin films than the conventional sintering method, .

A spray pyrolysis method, which is known as a chem­ical technique to fabricate superconducting thin films, is relatively simple and inexpensive. One of the problems en­countered is the rather low critical current density (Je).

The Je value in these films prepared by this method is usually in the range 10-100 A/cm2 at 77 K in zero mag­netic field,I-3 Recently, interesting experimental studies

which examined the melt-textured growth (MTG) of the bulk YBa2Cu307 _ x (YBCO) ceramics were reported. 4-7 These experiments showed that d.\.~ 1 c 'l'a.\.\l.~ ')l'a."- "-'--'b"-'--6...­

candy enhanced by a MTG processing. However, this method has not yet been examined in thin films except for a few studies, 8

We have applied this method to thin films, and ob-

4367 J. App\. Phys. 67 (9). 1 May 1990 0021-8979/90/094367 -03$03.00 © 1990 American Institute of Physics 4367

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