Sputtered YBa2Cu3Oy thin films on sapphire and silicon substrates using yttria stabilized ZrO2 buffer layers

PHYSICA

Physica C 180 (1991) 3 4 - 3 7 North-Holland

SPUTTERED YBa2Cu30 z THIN FILMS ON SAPPHIRE AND SILICON S U B S T R A T E S Y T T R I A STABILIZED ZrO 2 B U F F E R LAYERS H. SCHMIDT*,

K. HRADIL*,

*Siemens AG, Corp° +Siemens AG, Corp.

G. GIERES +' W. HOSLER*,

Research Research

and Development, and Development,

USING

AND Oo EIBL*

P.O.Box 830953, 8000 M~nchen 83, FRG P00.Box 3220, 8520 Erlangen, FRG

YBazCu30 x thin films w e r e d e p o s i t e d by sputtering on (1i02) sapphire and (i00) sillcon using an i n t e r m e d i a t e buffer layer of Y - s t a b i l i z e d ZrO 2 (YSZ). On sapphire the YSZ layer and the YBa2Cu.O grew epitaxially as was c o n f i r m e d by ion channeling and RBS. The c - o r i e n t e d ~ a 2 C u 3 0 x films had a T e of up to 90 K and je was 0°51.4 * 10 ° A / c m ~ at 77 K in zero m a g n e t i c field° On silicon the YSZ and the YBa2Cu30 x layer were h i g h l y textured, but polycrystalline° These YBa2Cu30 x films had T c values of up to 79 K.

i. I N T R O D U C T I O N For the i n t e g r a t i o n

were grown at substrate temperatures in m i c r o e l e c t r o -

nics and for m i c r o w a v e

applications

ranging

from 520 °C to 780 °C. The gas

pressure

in the d e p o s i t i o n

chamber was

Y B a 2 C u 3 0 x thin films have to be deposi-

1.6 Pa w i t h the gas c o n s i s t i n g

ted on s i l i c o n and on sapphire.

argon and 10% oxygen.

epitaxial

Direct

about

growth of Y B a 2 C u 3 0 x thin temperatures

interdiffusion

at e l e v a t e d

ted. U s i n g the same d e p o s i t i o n param e t e r s YSZ films were also d e p o s i t e d

which deteriorates

superconducting

100 nm thick films were deposi-

is hindered by

films on these substrates substrate

of 90 %

During one hour

properties.

the

Therefore,

Si-substrates

on

covered by native oxide.

The Y B a 2 C u 3 0 x thin films were deposited either by p l a n a r r f - m a g n e t r o n

sput-

w h i c h acts as d i f f u s i o n b a r r i e r and al-

tering or by p l a n a r DC sputtering.

For

lows the e p i t a x i a l

the d e p o s i t i o n

an e p i t a x i a l

b u f f e r layer is required growth of Y B a 2 C u 3 0 x

films w i t h high critical ties.

current densi-

Up to n o w MgO I and SrTi032 were

found as suitable b u f f e r layers on sapphire,

whereas

Y-stabilized

(YSZ) was used s u c c e s s f u l l y con 3,4.

ZrO 2

on sili-

In this study cubic YSZ was in-

rf-magnetron

of Y B a 2 C u 3 0 x films by

sputtering

stoichiometric

a ceramic non-

target w i t h c o m p o s i t i o n

Y B a 2 C u 3 . 3 0 x was used. The Cu rich target was chosen b e c a u s e p r e v i o u s l y deposited films w e r e found slightly poorer in their copper content compared to the

s u b s t r a t e materials.

target c o m p o s i t i o n 5o The YBa2Cu30 x films were grown at a gas pressure of

2. E X P E R I M E N T A L

parts argon and one part oxygen.

vestigated

as b u f f e r layer for both

70 Pa w i t h the gas consisting

The YSZ b u f f e r

layers were d e p o s i t e d

by p l a n a r r f - m a g n e t r o n

sputtering using

a target of Y - s t a b i l i z e d sapphire

and

substrates.

ZrO 2.

(i102)

(I00) silicon were used as The YSZ films on sapphire

epitaxial perature position.

of two

film growth a substrate

For tem-

of 740°C was chosen during deThe D C - s p u t t e r e d

YBa2Cu30 x

films were d e p o s i t e d in a separate sputter chamber with a diode configura

0921-4534/91/$03.50 © 1991 - Elsevier Science Publishers B.V.

All rights reserved.

H. Schmidt et al. / Sputtered YBa2Cu30x thin films on sapphire and silicon substrates

35

tion 6. For the deposition on YSZ/

600 °C and 720 °C were only weakly

sapphire the DC glow discharge ran in

textured,

pure oxygen at a pressure of 200 Pa

780 °C were single-crystalline.

yielding a deposition rate of 2nm/min.

crystal quality of the YSZ films was

whereas

films deposited at The

The distance between the target and the

also studied by ion channeling combined

substrate was 30 mm. In this case the

with Rutherford Backscattering Spectro-

substrate temperature was 720 °C. After

metry

deposition the YBa2Cu30 x films were

energy the minimum backscatter yield

cooled to room temperature in pure oxy-

(chimin)

(RBS). Using He ions of 2 MeV from the YSZ films was 0.06 to

gen at atmospheric pressure in about 30

0.09 of the yield for non-aligned

minutes.

orientation.

These values are compar-

able to values measured on single-crystals of reasonable perfection and con-

3. RESULTS AND DISCUSSION 3.1 YBa2Cu30 x ON YSZ/AI203 X-ray diffraction proved that all YSZ films were single phase and (h00)-ori-

firm the epitaxial growth of the YSZlayer on (li02)-sapphire.

The increase

of the backscatter yield at the inter-

ented except the YSZ film grown at

face between sapphire and YSZ is caused

520 °C. This film showed

by defects originating from the mis-

(hhh) reflec-

tions in addition to the (h00) reflec-

match between the (ii02) plane of hexa-

tions. YSZ films deposited between

gonal sapphire and the (001) plane of

FIGURE 1 High resolution TEM image of the YBa2Cu3-YSZ interface showing an intermediate BaZr03 layer

/ Sputtered

H. Schmidt et aL

36

cubic YSZ. At this interface mechanical

YBa2Cu30 . thin films on sapphire and silicon substrates

stoichiometry.

local

strain fields were also ob-

served by t r a n s m i s s i o n

electron micro-

scopy 7 .

Y B a 2 C u 3 0 x films were also deposited by DC-sputtering

on sapphire with YSZ buf-

fer layers 8. X - r a y d i f f r a c t i o n

The i n t e r f a c e Y B a 2 C u 3 O x / Y S Z

was studied

on a Y B a 2 C u 3 0 x film w h i c h was d e p o s i t e d by r f - m a g n e t r o n deposition

sputtering.

During the

of the Y B a 2 C u 3 0 x film at a

temperature

of 740 °C a 3-5 nm thick

intermediate

BaZrO 3 layer was formed

proved

that these films were h i g h l y c-textured.

Ion c h a n n e l i n g

on these films

showed a chimi n of 0.16

(Figure2) which

confirmed

growth of the

the epitaxial

Y B a 2 C u 3 0 x layer.

The 350 nm thick films

b e t w e e n the YSZ and the Y B a 2 C u 3 0 x (Fi-

had a T c of 90 K and Jc values of 1.21.4,106 A / c m 2 at 77 K in zero magnetic

gure i). The s t r a i g h t n e s s

field.

Y B a 2 C u 3 0 x lattice planes exhibits

of the in Figure 1

the good c r y s t a l l i n e

of the s u p e r c o n d u c t i n g the i n t e r m e d i a t e

quality

layer although

BaZrO 3 layer consists

3.2 Y B a 2 C u 3 0 x on Si/YSZ YSZ films d e p o s i t e d on Si(100) strates highly line.

of small regions with slight spread

sub-

covered by native oxide were (100)-textured,

but p o l y c r y s t a l -

The r f - s p u t t e r e d

Y B a 2 C u 3 0 x films

(max. 5 ° tilt)

in their orientation.

on these b u f f e r layers were c-oriented

Ion-channeling

on this c-oriented

and also p o l y c r y s t a l l i n e 9 . Deposited at

Y B a 2 C u 3 0 x film r e s u l t e d in a chimi n of 0.19 and the c o m p o s i t i o n was d e t e r m i n e d

800 °C these films had a T c of only

by RBS as Y0.gBa2.1CU3Ox.

sputtering

The m e a s u r e d

60 K, whereas pressure

films d e p o s i t e d by DC-

in pure oxygen with a gas

of 350 Pa at a lower substrate

T c of only 84 K and the reduced Jc of 5"105 A / c m 2 at 77K are a t t r i b u t e d to

temperature

the d e v i a t i o n

For an e p i t a x i a l

from the exact cation

of 685 °C had a T c of 79 K. growth of YSZ and

Y B a 2 C u 3 0 x the amorphous Energy 1.0 T

o.5 [

60

ved b y HF e t c h i n g or by e v a p o r a t i n g

(MeV) 1.5 I

2.O F

SiO 2 above now,

IC u i Ii [I i ;

E o = 2.0 MeV ~Z

i

r~l

non-epitaxial

i00

whereas e--beam

e v a p o r a t i o n 4,10 and laser ablation 3 are

I I

0

of

film growth could not be

(see alsol0),

known to result in epitaxial

,'i'f,I ,,/

the r e o x i d a t i o n

I, iB a

i

J

for

the silicon surface and c o n s e q u e n t l y a

L/ r a n d o m

\ :~

the

But up to

a p p l y i n g the sputter process

avoided

I oI

1100 °C in vacuum.

the YSZ d e p o s i t i o n y

':I

SiO 2 was remo-

/'< '

200

i \~L

YSZ films

on silicon. channeled

L

300

400

Channel

4. C O N C L U S I O N S Using Y - s t a b i l i z e d

ZrO 2 as buffer

layer Y B a 2 C u 3 0 x films with high critiFIGURE

2

RBS s p e c t r u m of the e p i t a x i a l YBa-Cu30 • Z X f~im on Y S Z / s a p p h i r e for r a n d o m orientation and for c h a n n e l i n g in <001>

cal current densities ter-deposited w h i c h makes

have been sput-

epitaxially

it a p r o m i s i n g

on sapphire, substrate

14. Schmidt et aL / Sputtered YBaFu30x thin films on sapphire and silicon substrates for superconducting

passive microwave

devices. Up to now the in-situ reoxidation the pre-cleaned

of epitaxial

YSZ

films on silicon.

The authors

thank B. Jobst for X-ray

diffraction

analyses,

technical

4. H. Myoren, Y. Nishiyama, N.Miyamoto, Y. Kai, Y. Yamanaka, Y. Osaka, and F. Nishiyama, Jap. J. Appl. Phys. 29 (1990) 955 5. H. Schmidt, R. Bruchhaus, O. Eibl, W. H6sler, L. Hofmann, W. Holubarsch, and G. Zorn, J. Less-CommonMet., 151 (1989) 411

ACKNOWLEDGEMENTS

patterning

3. D.K. Fork, A. Barrera, T.H. Geballe, A.M. Viano, and D.B. Fenner, Appl. Phys. Lett. 57 (1990) 2504

of

silicon has prevented

the sputter-deposition

G. Daalmans

for

the films and B. Sipos for assistance

concerning

6. H. Behner, G. Gieres, and B. Sipos, Proceed. ICMC'90, Topical Conf. High Temperature Superconductors, May 1990, Garmisch-Partenkirchen

the

sputter deposition of YBa2Cu30 x films. This work was supported by the BMFT,

7. O. Eibl, K. Hradil, in print

Federal Ministry

8. H. Schmidt, K. Hradil, W. Wersing, G. Gieres, Seeb6ck, in print

logy

37

of Science and Techno-

(13N5812).

REFERENCES i. A.B. Beresin, C.W. Yuan, and A.L. de Lozanne, Appl. Phys. Lett. 57 (1990) 90 2. K. Char, N. Mewman, S.M. Garrison, R.W. Barton, R.C. Taber, S.S. Laderman, and R.D. Jacowitz, AppI. Phys. Lett. 57 (1990) 409

and H. Schmidt, W. H6sler, and R.J.

9. H. Schmidt, O. Eibl, and B. Jobst, Proceed. ICMC'90, Topical Conf. High Temperature Superconductors, May 1990, Garmisch-Partenkirchen 10.H. Fukomoto, M. Yamamoto, and Y. Osaka, Proceedings Electrochemical Society 90-7 (1990) 239