A high quality superconducting film on a substrate with a low dielectric constant is desired for passive microwave circuit applications. In addition, it is essential that the patterning process does not effect the superconducting properties of the thin films to achieve the highest circuit operating temperatures. YBa2Cu3O7 superconducting films were grown on lanthanum aluminate substrates using laser ablation with resulting maximum transition temperature (T sub c) of 90 K. The films were grown on a LaAlO3 which was at 775 C and in 170 mtorr of oxygen and slowly cooled to room temperature in 1 atm of oxygen. These films were then processed using photolithography and a negative photoresist with an etch solution of bromine and ethanol. Results are presented on the effect of the processing on T(sub c) of the film and the microwave properties of the patterned films

Bhasin, K. B.

Bohman, D. Y.

Chorey, C. M.

Varaljay, N. C.

Warner, J. D.

English

NASA Technical Reports Server

NASA Technical Memorandum 102 tt"3_,
Growth and Patterning of Laser Ablated
Superconducting YBa2Cu307
Films on LaA103 Substrates
(NASA-lM-lO243cJ3 c,RL;N[H AND PATIERNI_IG
LASFR ABLA[_D SIJPERCONL)UCTINC, Yr_a?Cu3r)7
FILMS LJN LdAIr13 SUL_STRATES (NASA) d p
CSCL
OF _90-22q? I
20L Uncl is
G3/76 OZ7987d
J.D. Warner, K.B. Bhasin, N.C. Varaljay, and D.Y. Bohman
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio
and
C.M. Chorey
Sverdrup Technology, Inc.
NASA Lewis Research Center Group
Cleveland, Ohio
Prepared for the
36th National Symposium and Topical Conference
sponsored by the American Vacuum Society
Boston, Massachusetts, October 23-27, 1989
https://ntrs.nasa.gov/search.jsp?R=19900013105 2020-03-19T23:13:29+00:00Z

GROWTH AND PATTERNING OF LASER ABLATED SUPERCONDUCTING YBa2Cu3OT,
FILMS ON LaAIO 3 SUBSTRATES
J.D. Warner, K.B. Bhasin, N.C. Varaljay, D.Y. Bohman,
NASA Lewis Research Center Cleveland, OH 44135
C.M. Chorey'
Sverdrup Technology, Inc., NASA Lewis Research Center Group,
Cleveland, OH 44135
ABSTRACT
A high quality superconducting film on a substrate with a low
dielectric constant is desired for passive microwave circuit appli-
cations. In addition, it is essential that the patterning process
does not effect the superconducting properties of the thin films to
achieve the highest circuit operating temperatures. We have grown
YBa2Cu307 superconducting films on lanthanum aluminate substrates
using a laser ablation technique with resulting maximum transition
temperature (T=) of 90 K. The films were grown on LaAIO 3 which was at
775 °C and in 170 mtorr of oxygen and slowly cooled to room tempera-
ture in i atm of oxygen. These films were then processed using
photolithography and a negative photoresist with an etch solution of
bromine and ethanol. Results are presented on the effect of the
processing on T c of the film.
I. INTRODUCTION
Laser-ablated, high-temperature superconducting (HTS) YBa2Cu307
films have been made on many substrates including SrTiO 3, MgO,
LaGa03, and Zr02. _-7 These substrates were used because they either
had very small interaction with the HTS films during growth or
annealing or because the substrates with HTS films had potential
electronic applications. In this paper, we report on the growth and
patterning of thin YBa2Cu307 films on LaAIO 3 for microwave applica-
tions. LaAIO 3 was chosen as a substrate because of its relatively low
dielectric constant of 228 and because of it moderate loss tangent of
8x10 -_ at i0 GHz 9.
Lines varying in width from i0 to 20 _m were patterned using
photolithography and wet etching techniques. To determine if the
etching or lithography process had influenced the transition temper-
ature of the films. A ring resonator circuit operating at 35 GHz was
also fabricated, since the resonator allows the determination of
loss and dispersive properties of microstrip transmission line. From
the measurement of the quality factor "Q" of a resonator circuit one
can determine the microwave losses of the HTS films as compared with
those of gold on the same substrates.
*Work done under NASA contract #NAS3-25266; Regis Leonard, monitor.
II. Film Growth
The laser ablation technique used to grow the films on sub-
strates of LaAIO_is similar to the techniques reported in the
literature. I-7 The details of the geometry of the laser ablation is
shownin Fig. i. The substrates (15 by 15 by 0.25 mm)with orienta-
tion (001) were mounted onto a stainless steel plate with a dia-
meter of 63 mm. The plate was heated from the backside using a
resistive heater madefrom
LASER
VACUUM CHAMBER
LASER BEAM
.......... _ILASMA
HEATED SAMPLE
Figure 1. - Schematic of Ihe laser ablalion experiment,
Kanthal A-I wire (made by
Kanthal, Inc.). The temper-
ature was measured with a
type K thermocouple which
was welded to the plate.
The thermocouple was 2 mm
away from the sample. The
sample chamber was evacuated
to 3x10 -7 torr, or lower, us-
ing a liquid nitrogen cold
trapped diffusion pump be-
fore the sample was warmed
up to 500 °C. A continuous
flow of oxygen (120 sccm) was then introduced into the chamber, and
the sample heated to 775 =C. During deposition the chamber pressure
was 170 mtorr; the laser wavelength was 248 nm; the energy density
was 1.5 (J/cm2)/pulse; the pulse rate was 4 pps; and the distance
between the target and the sample was 8 cm. The laser beam was
rastered up and down i cm over the target using an external lens on
a translator. The angle between the laser beam and the normal to the
target was 45 ° . The target used was a sintered 25-mm-diameter pellet
of YBa2Cu_0v_ ×. After deposition the oxygen pressure was raised to i
atm, and the temperature was lowered to 450 °C at a rate of
2 °C/min. The temperature was held at 450 ° C for 2 hr before it was
lowered to 250 °C at a rate of 2 °C/min. The heater power was then
turned off, and the sample was allowed to cool to 40 °C or less
before it was removed the chamber.
The thickness of the HTS films on LaAIO 3 was estimated by measur-
ing the thickness of a film grown on quartz plate that was shadow
masked. The quartz plate had been placed i mm below the bottom of
the LaAIO 3 on the substrate holder such that the sweep of the plasma
plumb was along the line connecting the centers of the quartz and
the LaAIO].
The best film had a T c of 89.8 K immediately after deposition as
determined by a standard four point resistance measurement. Its
resistance versus temperature behavior is shown in Fig.2. From the
intercept of the extrapolated resistance at 0 K and from the resis-
tance above To, one can see that the film is c-axis aligned. This is
confirmed by only having the (001) peaks in the x-ray diffraction
data (Fig. 3). The surface morphology of the HTS on LaAIOj is shown
in Fig. 4. The surface is very smooth with some small structure. We
do not observe large numbers of HTS particulates due to the laser
ablation process.
1.0 --
0.8 --
o. 6
0.4
0.2
_J
0
0
0
0
0
_ ©
0
.5 r :f
r
-- '] i _'
-- 0 84 88 92 %
_l_J_A_& ____l____L_l_J__i J
60 120 180 240 _00
TEMPERA I-URE, K
Figure 2 - Normalized resislance of laser abLaled
YBa2Cu30 × film on LaAIO 3
( 0062.00 r--
I
1.62 ---
1.28 i_''-
0.98 _--
0.72 --
0.50 --- _oos_ t
032_ i I
o.08 -  oo2,1,oo ,,t 1  oo7 , 1
o o2_(°°1) I 1(_oo),,"I 11!.2°%" I
0 10 20 30 40 50 60 10 80
20
Figure 3. - X-ray aiffrac:,,on 2,a,ttern of laser ao_atec
Y£a2Cu30 × film on LaAIO 3.
Figure 4. - Scanning electron micrograph of laser ablated YBa 2Cu 3Ox
Film on LaAIO 3.
3
ORIGIN/_L PAGE !S
0I: POOR QUALITY
PATTERNING
Films on LaAIO 3 and SrTiO 3 were patterned using photolithography
and wet etching. The negative photoresist (752), its developer
Table I Effect of Photolithography Process
on T c of YBa2Cu30 x Films
Exposure to negative photoresist None
Soft baking of photoreslstet9_ °C
for 1 hr) None
Exposure to photoresistdeveloper
end rinse None
Exposure to different stripping solvents
ifter pitternln_:
Boiling ascetone (58 °C) for I_ min None
Boiling ethsnol (78 °C) for IS min None
Boiling toluene (111 °C) for lg min None
Losllin IV (7B_ °C) for 5 min None
a0nly boil_ng ethanol snd Losilln IV sucessfully
removed exposed phoresist.
(802), and the assoc-
iated rinse (n-butyl
acetate) used were ob-
tained from KTI. The
photoresist strippers
used were Losalin IV
(from E.C. Merke),
acetone, toluene, and
ethanol. Each step of
the process was
checked to see if it
had an effect on the
Tc of the HTS films.
The results of the
different processing
steps on T c are shown
in table I. The full
process of patterning
the HTS films was to
spin on the negative
photoresist to a thickness of 2 _m, followed by a soft bake at 90 °
C for i hr, and then to expose the photoresist. After developing the
photoresist, the film was etched for 500 s in i percent molar of
bromine in ethanol. After etching, the films were rinsed in ethanol
and the photoresist was removed with the Losalin IV photoresist
stripper which was at 70 °C. We did not observed any drop in the T c
of the HTS films.
1,0 --
0.9--
0.8'--
0.7--
-< o.6-
0.5--
N
-- 0.4--
_ 0.3--
0.2 _--
O. _
0
50
=
D
! i i ! ', i
100 150 200 250 300
TEI'IPERATURE,K
Figure 5. - Normalized resistance of a laser ablated
YBa2Cu30 x film on SrTi03. The film [] is before pro-
cessing while the film • is after exposure to negative
photoresist.
The films used to
determine the effect of
the various fabrication
steps had transition
temperatures between 77
and 85 K. Fig. 5 shows
the effect of exposing
the film directly to the
photoresist stripper
Losalin IV at 70 ° C. No
change in T c occurred,
but the slope of the re-
sistance versus tem-
perature curve did
change. Fig. 6 shows the
T e of the film on LaAI03
before patterning and
after it was patterned
into a ring resonator,
that had operated at 33
GHz, and after it had
].OF--
0.gL-
L
0.8 i
o.z--
Z i
_._ 0.6 '----
o.5_-
0.4 t
< t
_.- 0.3'.,--
I
0.2--
i
0.1---
i
oi
5O
÷
÷
:J-
J
m
mmm maf
a
m
100 150 200 250 300
TEMPERATURE, K
Figure 6. - Comparison of normah:'ed resJs:ance of a _aser
ablated YBa2Cu30× fiJm on LaAI©3 before prccessing
and after being fazncatec_ _nto a 35-GHz nng resonator,
silver contacts evapo-
rated onto it and an-
nealed at 500 ° C for
i hr. There is no appar-
ent difference in the Tc
or the resistance versus
temperature behavior be-
tween the film before
and after processing.
To test the laser
ablation technique's
ability to produce uni-
form film thickness and
the variation of Tc
across the film, Hall
bars with silver con-
tacts were fabricated
(Fig. 7). The width of
the bar is i0 _m. The
film thickness is not
very uniform over the 5-
by lO-mm area. The time
needed to etch the film
until the substrate was exposed varied by a factor of 2 from one
edge to the other edge of the substrate. However, the Tc did not vary
from region to region (table II).
Figure 7. - Finished Hall bar of YBa2Cu30 _ film on SrTiO 3 substrate.
Table II Variation of on SrTiO B
as Measured With Patterned Hall Bars
Before patterning 70.8 K
10- #m lines after patterning 71.0, 71.5, 72.5 K
20- _m lines after patterning 75.3, 75.5, 76.5 K
5
ORI(_INAL PAGE IS
OF POOR QUALITY
Conclusions
Laser-ablated, high-temperature superconducting films on LaAIO_
and SrTiO_ have been grown. The best films had a T c of 90 K and have
their c-axis aligned to the substrate. There is no variation of T c
across the films, but there is a variation of film thickness. These
films have been patterned with negative photoresist and a bromine/
ethanol etch. There is no detectable degradation of T c by any step of
the fabrication process even though the films were heated to 122 ° C
in toulene.
This fabrication process should be able to be used to make most
of the passive and one layer structures without any degradation of
the transition temperature.
REFERNCES
i. J.D. Warner, J.E. Meola, and K.A. Jenkins, NASA TM-I02350, 1989.
2. D. Dijkkamp, T. Venkatesan, X.D. Wu, S.A. Shaheen, N. Jisrawi,
Y.H. Min-Lee, and W.L. Mclean, M. Croft, Appl. Phys. Lett. 51, 619
(1987).
3. X.D. Wu, D. Dijkkamp, S.B. 0gale, A. Inam, E.W. Chase, P.F.
Miceli, C.C. Chang, J.M. Tarascon, and T. Venkatesan, Appl.
Phys. Lett. 51, 861 (1987).
4. J. Narayan, N. Biunno, R. Singh, 0.W. Holland, and O. Auciello,
Appl. Phys. Lett. 51, 1845 (1987).
5. L. Lynds, B.R. Weinberger, G.G. Peterson, and H.A. Kransinski,
Appl. Phys. Lett. 52, 320 (1988).
6. T. Venkatesan, C.C. Chang, D. Dijkkamp, S.B. 0gale, E.W. Chase,
L.A. Farrow, D.M. Hwang, P.F. Miceli, S.A. Shwarz, J.M. Tarascon,
X. D. Wu, and A. Inam, J. Appl. Phys. 63, 4591 (1988).
7. A.M. Desantolo, M.L. Mandich, S. Sunshine, B.A. Davidson, R.M.
Fleming, P. Marsh, and T.Y. Kometani, Appl. Phys. Lett. 52, 1995
(1988)
8. F.A. Miranda, W.L. Gordon, V.O. Heinen, B.T. Ebihara, and K.B.
Bhasin, NASA TM-I02123, 1989.
9. R.W. Simon, C.E. Platt, A.E. Lee, G.S. Lee, and K. Daly, Appl.
Phys. Lett., 53, 2677 (1988).
Report Documentation PageNational Aeronautics and
Space Administration
1. Report NO. 2, Government Accession No. 3. Recipient's Catalog No,
NASA TM-102 g'//_
5. Report Date4. Title and Subtitle
Growth and Patterning of Laser Ablated Superconducting YBa2Cu30_
Films on LaAIO3 Substrates
7. Author(s)
J.D. Warner, K.B. Bhasin, N.C. Varaljay, D.Y. Bohman, and
C.M. Chorey
9. Performing Organization Name and Address
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
12. Sponsoring Agency Name and Address
National Aeronautics and Spacc Administration
Washington, D.C. 20546-0001
6. Performing Organization Code
8. Performing Organization Report No.
E-5205
10. Work Unit No.
307-51-00
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared for the 36th National Symposium and Topical Conference, sponsored by the American Vacuum
Society, Boston, Massachusetts, October 23-27, 1989. J.D. Warner, K.B. Bhasin, N.C. Varaljay, and
D.Y. Bohman, NASA Lewis Research Center; C.M. Chorey, Sverdrup Technology, Inc., NASA Lewis
Research Center Group, Cleveland, Ohio 44135.
16. Abstract
A high quality superconducting film on a substrate with a low dielectric constant is desired for passive microwave
circuit applications. In addition, it is essential that the patterning process does not effect the superconducting
properties of the thin films to achieve the highest circuit operating temperatures. We have grown YBa2Cu307
superconducting films on lanthanum aluminate substrates using laser ablation with resulting maximum transition
temperature (T,.) of 90 K. The films were grown on LaAIO3 which was at 775 °C and in 170 mtorr of oxygen
and slowly cooled to room temperature in 1 atm of oxygen. These films were then processed using photolithography
and a negative photoresist with an etch solution of bromine and ethanol. Results are presented on the effect of the
processing on Tc of the film and the microwave properties of the patterned films.
17. Key Words (Suggested by Author(s))
Laser ablation; HTS; Superconductor; High temperature
superconductor; LaAIO3: Thin film; Patterning
18, Distribution Statement
Unclassified- Unlimited
Subject Category 76
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of pages
Unclassified Unclassified 8
NASAFORM1626OCT86 *For sale by the National Technical Information Service, Springfield, Virginia 22161
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Growth and patterning of laser ablated superconducting YBa2Cu3O7 films on LaAlO3 substrates

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