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TiBaCaCuO-films for passive microwave devices
PHYSICA
Physica C 201 (1992) 337-339 North-Holland
TiBaCaCuO-films for passive microwave devices M. Manzel a, H. Bruchlos a, E. SteinbeiB a, T. Eick a, M. Klinger b, j. Fuchs c and B. Kley c a InstitutfurPhysikalischeHochtechnologie, Helmholtzweg4, D-6900Jena, Germany b Forschungsgesellschaft far lnformationstechnik, Bodenburger Str., D- 3202 Bad Salzdetfurth, Germany c Friedrich-Schiller-Universitiit Jena, IAP, Max-Wien-Platz 1, 1)-6900 Jena, Germany
Received 25 July 1992 Revised manuscript received 26 August 1992
Superconducting T1BaCaCuO-fflmswere prepared by a two-step method. The TI-HTSC films on LaA103-substrates are singlephase, highly c-axis oriented, and have critical temperatures up to 116 IC The films have surface resistances of 35 mfl at 77 K and 92 GHz and were tested for microwave devices. Furthermore we propose a new structuring method for the fabrication of microwave devices made of T1-HTSC-Fflms.
1. Introduction The fabrication of passive microwave components using high-temperature superconducting films (HTSC) requires films with high critical temperatures (To) and low surface resistances (Rs) at operating frequencies. The ability to grow the superconducting films on both sides of large area substrates can enhance the performance of RF microstrip devices. Therefore a film preparation technique, which produces highly c-axis oriented T1BaCaCuO-films on both sides of a LaA103 substrate, is very desirable. Such films were used in the fabrication of resonators and filters in the U H F region.
2. Thin film preparation The films were p r e p a r e d by a two-step m e t h o d [ 1,2 ]. As a first step B a - C a - C u - O precursor films were sputter d e p o s i t e d on b o t h sides o f a LaAIO3 substrate a n d then Tl was i n c o r p o r a t e d by post annealing in a Tl-oxide l o a d e d atmosphere. T h e precursor films were reactively d e p o s i t e d from a metallic B a - C a - C u alloy target by m e a n s o f a D C high rate sputtering. Selective resputting effects can be suppressed at high d e p o s i t i o n rates ( R > 5 0 n m / m i n ) , because the d e s o r p t i o n rate o f the alkaline
earth-metal c o m p o n e n t s was found to be nearly ind e p e n d e n t o f the deposition rate [ 2 ]. The D C sputtering o f the precursor films was c a r d e d out u n d e r the conditions listed in table 1. The as-deposited films on ( 1 0 0 ) LaA103 substrate were a m o r p h o u s , isolating, and a p p e a r mirrorsmooth. T1 was i n c o r p o r a t e d in the precursor films by post annealing in a Tl-oxide l o a d e d a t m o s p h e r e for l 0 m i n at 1140 K and subsequent cooling in 02 with a special t e m p e r a t u r e - t i m e p r o g r a m m . During this step the sample, d e p o s i t e d on b o t h sides o f the substrate, was enclosed in a gold foil bag together with two presintered pellets o f T1-HTSC bulk ceramic. T1diffusion experiments with pellets o f different compositions (2223, 2222, a n d 2201 ) have shown that T12Ba2Ca2CuEOx is an useful c o m p o s i t i o n with respect to the durability o f the Tl-diffusion source. D e p t h profiles, m e a s u r e d by means o f secondary neutral mass spectrometry, indicate that Tl is hoTable 1 Sputtering conditions Target DC power Sputtering gas Sputtering pressure Substrate temperature Substrate-target spacing
0921-4534/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
~ = 80 mm Ba2Ca2Cu3-aUoy 275 W 90% Ar+ 10% 02 1 Pa 500 K 50 mm
338
M. Manzel et al. / TIBaCaCuO-films for passive microwave devices
Table 2 Structure parameters Crystal structure Dominant phase Lattice constant Halfwidth of rocking curve
polycrystalline, grain size about 10 lain 2223 c= 35, 648 A <1.5 °
Table 3 Superconducting properties Transition temperature AC-susceptibility transition width (90-10% ) Critical current density at 77 K (H = 100 kA/m perpendicular to the film normal ) Surface resistance at 77 K and 92 GHz
>IlOK
3. Film properties
/
~100
./
2c
4 ""----
r7
/ ¢
J
10
10
20 30 40 50 60 70 80 90 100 110 Temperature / K Fig. 1. Temperature dependence of the surface resistance Rs for a T1BaCaCuO-film, measured at 92 GHz. mogeneously distributed in the annealed thin T1HTSC-fdm. However, the annealing process is a very critical technology step, in which the precursor film is leaded with TI, simultaneously crystallized, and fully oxidized. The two-step (deposition + annealing) can also be used successfully for the preparation of large-area TIBaCaCuO-film on both sides of monocrystalline substrates.
The superconducting properties of the T1BaCaCuO-films depend sensitively on the morphology, phase composition, and texture of the films. We could demonstrate [3 ] that T1-HTSC-films with low surface resistance Rs are characterized by a well-developed coarse-grain crystal structure, high degree of caxis orientation, and high phase purity, expressed not only in the X-ray diagram but also in the sharpness o f the AC-susceptibility transition near To. Typical parameters of the structure are listed in table 2. The films are approximately 1 ~tm thick and are grown on both sides of the LaA103 substrates. The T1-HTSC-films having the mentioned structure parameters show the following superconducting properties (table 3). The temperature dependence of the surface resistance Rs of a T1BaCaCuO-film, measured with a Ho~ lresonator, is shown in fig. 1. The reached Revalues are sufficiently low for microwave device fabrication [5,6].
4. Film patterning method For the preparation o f planar passive microwave devices made of TI-HTSC films the structuring process of the accomplished films has the disadvantage that the structuring equipments are contaminated with toxic Tl-compounds. Moreover, the edges o f the striplines, carrying the highest current densities [ 4 ],
M. Manzel et aL / TIBaCaCuO-films for passive microwave devices
are disturbed by the structuring process. Therefore we have tested a new method for the fabrication of planar microwave devices. We pattern the Tl-free precursor films and adjust the superconducting properties of the structured film by annealing in the well known manner. The usefulness of this technology was proved on functioning 4 G H z half-wavelength microstrip resonators. We obtained unloaded quality factors at 77 K up to 1000 at - 50 dBm input power, which are lower than expected from the Rs values. Therefore the improvement of the annealing process of the patterned precursor films is now under investigation.
Acknowledgements The authors thank J,H. Hinken, F.I.T., Bad Salzdetfurth, for valuable discussions and B. Conrad for
339
technical assistance. This work was supported by BMFT under Grant Nr. FKZ 13 N 5927.
References [ 1 ] C.X. Qiu and I. Shih, Appl. Phys. Lett. 53 (1988) 1122. [2] M. Manzel, H. Bruchlos, G. Bruchlos, T. Eick, E. SteinbeiB and L. Illgen, Phys. Status Solidi A 128 ( 1991 ) 175. [3] M. Manzel, H, Bruchlos, G. Brnchlos, T. Eick, E. SteinbeiB, M. Klinder and G. Eimbeck, Phys. Status. Solidi. A 131 ( 1992 ) K43. [4] J. Wolff, Einf'tihrung in die Mikrostrip-Leitungstechnik, Teil I.: Die Leitungen (Wolff, Aachen, 1985 ) p. 78. [5] R.B. Hammond, G.V. Negrete, L.C. Bourne, D.D. Strother, A.H. Cardona and M.M. Eddy, Appl. Phys. Lett. 57 (1990) 825. [6] W.L. Holstein, L.A. Parisi, D.J. Kountz, C. Wilker, A.L. Matthews, P.N. Arendt and R.C. Taber, IEEE rans. Magn. 27 (1991) 1568.
Physica C 201 (1992) 337-339 North-Holland
TiBaCaCuO-films for passive microwave devices M. Manzel a, H. Bruchlos a, E. SteinbeiB a, T. Eick a, M. Klinger b, j. Fuchs c and B. Kley c a InstitutfurPhysikalischeHochtechnologie, Helmholtzweg4, D-6900Jena, Germany b Forschungsgesellschaft far lnformationstechnik, Bodenburger Str., D- 3202 Bad Salzdetfurth, Germany c Friedrich-Schiller-Universitiit Jena, IAP, Max-Wien-Platz 1, 1)-6900 Jena, Germany
Received 25 July 1992 Revised manuscript received 26 August 1992
Superconducting T1BaCaCuO-fflmswere prepared by a two-step method. The TI-HTSC films on LaA103-substrates are singlephase, highly c-axis oriented, and have critical temperatures up to 116 IC The films have surface resistances of 35 mfl at 77 K and 92 GHz and were tested for microwave devices. Furthermore we propose a new structuring method for the fabrication of microwave devices made of T1-HTSC-Fflms.
1. Introduction The fabrication of passive microwave components using high-temperature superconducting films (HTSC) requires films with high critical temperatures (To) and low surface resistances (Rs) at operating frequencies. The ability to grow the superconducting films on both sides of large area substrates can enhance the performance of RF microstrip devices. Therefore a film preparation technique, which produces highly c-axis oriented T1BaCaCuO-films on both sides of a LaA103 substrate, is very desirable. Such films were used in the fabrication of resonators and filters in the U H F region.
2. Thin film preparation The films were p r e p a r e d by a two-step m e t h o d [ 1,2 ]. As a first step B a - C a - C u - O precursor films were sputter d e p o s i t e d on b o t h sides o f a LaAIO3 substrate a n d then Tl was i n c o r p o r a t e d by post annealing in a Tl-oxide l o a d e d atmosphere. T h e precursor films were reactively d e p o s i t e d from a metallic B a - C a - C u alloy target by m e a n s o f a D C high rate sputtering. Selective resputting effects can be suppressed at high d e p o s i t i o n rates ( R > 5 0 n m / m i n ) , because the d e s o r p t i o n rate o f the alkaline
earth-metal c o m p o n e n t s was found to be nearly ind e p e n d e n t o f the deposition rate [ 2 ]. The D C sputtering o f the precursor films was c a r d e d out u n d e r the conditions listed in table 1. The as-deposited films on ( 1 0 0 ) LaA103 substrate were a m o r p h o u s , isolating, and a p p e a r mirrorsmooth. T1 was i n c o r p o r a t e d in the precursor films by post annealing in a Tl-oxide l o a d e d a t m o s p h e r e for l 0 m i n at 1140 K and subsequent cooling in 02 with a special t e m p e r a t u r e - t i m e p r o g r a m m . During this step the sample, d e p o s i t e d on b o t h sides o f the substrate, was enclosed in a gold foil bag together with two presintered pellets o f T1-HTSC bulk ceramic. T1diffusion experiments with pellets o f different compositions (2223, 2222, a n d 2201 ) have shown that T12Ba2Ca2CuEOx is an useful c o m p o s i t i o n with respect to the durability o f the Tl-diffusion source. D e p t h profiles, m e a s u r e d by means o f secondary neutral mass spectrometry, indicate that Tl is hoTable 1 Sputtering conditions Target DC power Sputtering gas Sputtering pressure Substrate temperature Substrate-target spacing
0921-4534/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
~ = 80 mm Ba2Ca2Cu3-aUoy 275 W 90% Ar+ 10% 02 1 Pa 500 K 50 mm
338
M. Manzel et al. / TIBaCaCuO-films for passive microwave devices
Table 2 Structure parameters Crystal structure Dominant phase Lattice constant Halfwidth of rocking curve
polycrystalline, grain size about 10 lain 2223 c= 35, 648 A <1.5 °
Table 3 Superconducting properties Transition temperature AC-susceptibility transition width (90-10% ) Critical current density at 77 K (H = 100 kA/m perpendicular to the film normal ) Surface resistance at 77 K and 92 GHz
>IlOK
3. Film properties
/
~100
./
2c
4 ""----
r7
/ ¢
J
10
10
20 30 40 50 60 70 80 90 100 110 Temperature / K Fig. 1. Temperature dependence of the surface resistance Rs for a T1BaCaCuO-film, measured at 92 GHz. mogeneously distributed in the annealed thin T1HTSC-fdm. However, the annealing process is a very critical technology step, in which the precursor film is leaded with TI, simultaneously crystallized, and fully oxidized. The two-step (deposition + annealing) can also be used successfully for the preparation of large-area TIBaCaCuO-film on both sides of monocrystalline substrates.
The superconducting properties of the T1BaCaCuO-films depend sensitively on the morphology, phase composition, and texture of the films. We could demonstrate [3 ] that T1-HTSC-films with low surface resistance Rs are characterized by a well-developed coarse-grain crystal structure, high degree of caxis orientation, and high phase purity, expressed not only in the X-ray diagram but also in the sharpness o f the AC-susceptibility transition near To. Typical parameters of the structure are listed in table 2. The films are approximately 1 ~tm thick and are grown on both sides of the LaA103 substrates. The T1-HTSC-films having the mentioned structure parameters show the following superconducting properties (table 3). The temperature dependence of the surface resistance Rs of a T1BaCaCuO-film, measured with a Ho~ lresonator, is shown in fig. 1. The reached Revalues are sufficiently low for microwave device fabrication [5,6].
4. Film patterning method For the preparation o f planar passive microwave devices made of TI-HTSC films the structuring process of the accomplished films has the disadvantage that the structuring equipments are contaminated with toxic Tl-compounds. Moreover, the edges o f the striplines, carrying the highest current densities [ 4 ],
M. Manzel et aL / TIBaCaCuO-films for passive microwave devices
are disturbed by the structuring process. Therefore we have tested a new method for the fabrication of planar microwave devices. We pattern the Tl-free precursor films and adjust the superconducting properties of the structured film by annealing in the well known manner. The usefulness of this technology was proved on functioning 4 G H z half-wavelength microstrip resonators. We obtained unloaded quality factors at 77 K up to 1000 at - 50 dBm input power, which are lower than expected from the Rs values. Therefore the improvement of the annealing process of the patterned precursor films is now under investigation.
Acknowledgements The authors thank J,H. Hinken, F.I.T., Bad Salzdetfurth, for valuable discussions and B. Conrad for
339
technical assistance. This work was supported by BMFT under Grant Nr. FKZ 13 N 5927.
References [ 1 ] C.X. Qiu and I. Shih, Appl. Phys. Lett. 53 (1988) 1122. [2] M. Manzel, H. Bruchlos, G. Bruchlos, T. Eick, E. SteinbeiB and L. Illgen, Phys. Status Solidi A 128 ( 1991 ) 175. [3] M. Manzel, H, Bruchlos, G. Brnchlos, T. Eick, E. SteinbeiB, M. Klinder and G. Eimbeck, Phys. Status. Solidi. A 131 ( 1992 ) K43. [4] J. Wolff, Einf'tihrung in die Mikrostrip-Leitungstechnik, Teil I.: Die Leitungen (Wolff, Aachen, 1985 ) p. 78. [5] R.B. Hammond, G.V. Negrete, L.C. Bourne, D.D. Strother, A.H. Cardona and M.M. Eddy, Appl. Phys. Lett. 57 (1990) 825. [6] W.L. Holstein, L.A. Parisi, D.J. Kountz, C. Wilker, A.L. Matthews, P.N. Arendt and R.C. Taber, IEEE rans. Magn. 27 (1991) 1568.