- Email: [email protected]
Low-temperature method for thin superconducting films preparation
Physiea C 162-164 (1989) 629-630 North-Holland
L O W - T ~ P E R A T U R E METHOD POR THIN SUPERCONDUCTING PII~S PREPARATION V.M.Puzikov, A.V.Semyonov, D.I.Zoslm, V.L.Dubonosov, L.S.Zolotovitskaya, R.P.Ramakayeva Research Institute for Single Crystals, Lenin av.60, 310141, Kharkov, USSR The suggested method for the low-temperature synthesis (T= < 400 oC) of the HTSC films, that does not require annealing, significantly broadens the class of the substrete materials and allows to apply this technique for the semiconducting devices production. 1. INTRODUCTION Already known methods for films preparation allow to obtain high-quality layers mainly on SrTi03, MgO or on other substrates (A1203, Si) but with preliminary deposition of special sublayers (e.g. Zr02). When depositing films directly on such substrates as Si, A1203, GaAs, due to high synthesis temperatures ( > 600 °C) (or annealing), interdiffusion of the elements of substrafe and film results in essential deterioration of the HTSC parameters of the film. Aiming to decrease the temperatures of the synthesis (below 300 °C) and to develop a technique that would not require annealing of the HTSC films, we studied the possibility to use the method of the discrete pulsed thermal evaporation. 2. EXPERIMENTAL The matter of the technique is as follows: conventionally prepared superconducting Y-Ba20u307_ x powder was used as an initial material. The average size of the particles was 5~Am. The powder was fed from a weigher to the evaporator. The evaporator of tungsten was heated by a circular electron-beam gun 0921-4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
up %o-~ 2000 °C. The evaporator temperature and the rate of the powder feeding are chosen so that the evaporation of the delivered particles of the powder occurs contactlessly (for the time N10-3-10-2s) which promotes practically isotropic mass transfer of the substance onto a substrate. The rate of deposition was SOOO - 2000 D m i n . The temperature of substrates did not exceed 250 °C. The choice of the substrate temperatures (~250 °C) can be explained by the fact that according %o the thermographimetry data, the oxygen loss from Y-Ba-Cu-O lattice is minimal at such temperatures and practically all the entering oxygen remains in the film lattice. At the film temperatures ~ 2 5 0 °0 the increase of the oxygen loss from the lattice was observed. The pressure in the chamber was 1-10 -5 mm Hg during the deposition p r o cess.
The study o f the effect of temperature of evaporator, size of particles and rate of their entering the evaporator, temperature of substrates on composition and structure of substrates made it possible %o determine the conditions for the synthesis, at which the
V.M. Puzikov et al. / Thin superconducting filrn preparation
630
film composition actually corresponded
boundary (~30-50 ~)
to the I-2-3 one
and the substrate which is , a n evidence
with the oxygen con-
centration >6.5 of formula units.
of the absence of their diffusional in-
The obtained films were polycrystalllne. Spaces between
crystallites
between the film
of
teraction are well seen from these curYeS,
@
C, ~ormUlauni~s Y~a 2 C u ~ f f
800-1000 A are filled with textured poO
lycrystalline formation of ~ 100 A and less. It should be noted that the structure of films practically did not
de-
pend on the type of the studied substrates.
I
3 I I
Ba
2
~A
I I
4
Y I
I
r
I ! •
!
I
q 5 6789
10 m,rn~/mi.
i~I GURE 2 Elements ratio in the YBa2Cu307_ x film dependence upon the mass of entering material. High uniformity is
80 1~0 ZOO2~05003qO ~K
probably due to
the fact, that in the said
TIGURE 1 Dependence of the electric resistance of the Y-Ba-Cu-O films on temperature.
evaporation as a flash
technique
of the components avoiding a
liquid
occurs stage,
which promotes an isotropic transfer of 0nly some difference can be seen on the R(T) curves (Pig.S),
which is pro-
all the components. ~ormation of the crystalline
struc-
bably associated with different content
ture of films is at the first sight un-
of oxygen in films and with some diffe-
expectable at such low temperatures
rence in the conditions for deposition.
synthesis. However, it should be taken into account, that an ion component,
Pilms, prepared by the mentioned technique, are superconducting following annealing.
without
Irrespective
a of
of
present in the limits of I-1.5 % in the flow of the deposited material, can
the type of a substrate, films have si-
play a definite role.
Bombardment
milar parameters (T c = 78-88 K) (T c = = 0.7-2 K). The thickness of films is
the substrate by ions
with the energy
in the range of 0. I - 1 . 0 ~ m . The curves of the profile auger-analysis, are presented in Fig. 2. An especially high uniformity of the films over the depth as well as a distinct
of
of ~ I-2 keV allows to increase the concentration of the crystallization centers, which is analogous to decreasing the degree of saturation of the deposition of the deposited material, necessary for the structure formation.
L O W - T ~ P E R A T U R E METHOD POR THIN SUPERCONDUCTING PII~S PREPARATION V.M.Puzikov, A.V.Semyonov, D.I.Zoslm, V.L.Dubonosov, L.S.Zolotovitskaya, R.P.Ramakayeva Research Institute for Single Crystals, Lenin av.60, 310141, Kharkov, USSR The suggested method for the low-temperature synthesis (T= < 400 oC) of the HTSC films, that does not require annealing, significantly broadens the class of the substrete materials and allows to apply this technique for the semiconducting devices production. 1. INTRODUCTION Already known methods for films preparation allow to obtain high-quality layers mainly on SrTi03, MgO or on other substrates (A1203, Si) but with preliminary deposition of special sublayers (e.g. Zr02). When depositing films directly on such substrates as Si, A1203, GaAs, due to high synthesis temperatures ( > 600 °C) (or annealing), interdiffusion of the elements of substrafe and film results in essential deterioration of the HTSC parameters of the film. Aiming to decrease the temperatures of the synthesis (below 300 °C) and to develop a technique that would not require annealing of the HTSC films, we studied the possibility to use the method of the discrete pulsed thermal evaporation. 2. EXPERIMENTAL The matter of the technique is as follows: conventionally prepared superconducting Y-Ba20u307_ x powder was used as an initial material. The average size of the particles was 5~Am. The powder was fed from a weigher to the evaporator. The evaporator of tungsten was heated by a circular electron-beam gun 0921-4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
up %o-~ 2000 °C. The evaporator temperature and the rate of the powder feeding are chosen so that the evaporation of the delivered particles of the powder occurs contactlessly (for the time N10-3-10-2s) which promotes practically isotropic mass transfer of the substance onto a substrate. The rate of deposition was SOOO - 2000 D m i n . The temperature of substrates did not exceed 250 °C. The choice of the substrate temperatures (~250 °C) can be explained by the fact that according %o the thermographimetry data, the oxygen loss from Y-Ba-Cu-O lattice is minimal at such temperatures and practically all the entering oxygen remains in the film lattice. At the film temperatures ~ 2 5 0 °0 the increase of the oxygen loss from the lattice was observed. The pressure in the chamber was 1-10 -5 mm Hg during the deposition p r o cess.
The study o f the effect of temperature of evaporator, size of particles and rate of their entering the evaporator, temperature of substrates on composition and structure of substrates made it possible %o determine the conditions for the synthesis, at which the
V.M. Puzikov et al. / Thin superconducting filrn preparation
630
film composition actually corresponded
boundary (~30-50 ~)
to the I-2-3 one
and the substrate which is , a n evidence
with the oxygen con-
centration >6.5 of formula units.
of the absence of their diffusional in-
The obtained films were polycrystalllne. Spaces between
crystallites
between the film
of
teraction are well seen from these curYeS,
@
C, ~ormUlauni~s Y~a 2 C u ~ f f
800-1000 A are filled with textured poO
lycrystalline formation of ~ 100 A and less. It should be noted that the structure of films practically did not
de-
pend on the type of the studied substrates.
I
3 I I
Ba
2
~A
I I
4
Y I
I
r
I ! •
!
I
q 5 6789
10 m,rn~/mi.
i~I GURE 2 Elements ratio in the YBa2Cu307_ x film dependence upon the mass of entering material. High uniformity is
80 1~0 ZOO2~05003qO ~K
probably due to
the fact, that in the said
TIGURE 1 Dependence of the electric resistance of the Y-Ba-Cu-O films on temperature.
evaporation as a flash
technique
of the components avoiding a
liquid
occurs stage,
which promotes an isotropic transfer of 0nly some difference can be seen on the R(T) curves (Pig.S),
which is pro-
all the components. ~ormation of the crystalline
struc-
bably associated with different content
ture of films is at the first sight un-
of oxygen in films and with some diffe-
expectable at such low temperatures
rence in the conditions for deposition.
synthesis. However, it should be taken into account, that an ion component,
Pilms, prepared by the mentioned technique, are superconducting following annealing.
without
Irrespective
a of
of
present in the limits of I-1.5 % in the flow of the deposited material, can
the type of a substrate, films have si-
play a definite role.
Bombardment
milar parameters (T c = 78-88 K) (T c = = 0.7-2 K). The thickness of films is
the substrate by ions
with the energy
in the range of 0. I - 1 . 0 ~ m . The curves of the profile auger-analysis, are presented in Fig. 2. An especially high uniformity of the films over the depth as well as a distinct
of
of ~ I-2 keV allows to increase the concentration of the crystallization centers, which is analogous to decreasing the degree of saturation of the deposition of the deposited material, necessary for the structure formation.