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High temperature superconducting films on flexible substrates for cryoelectronics
Physica C 357±360 (2001) 1368±1372
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High temperature superconducting ®lms on ¯exible substrates for cryoelectronics K.S. Harshavardhan a,*, H. Christen a, S.D. Silliman a, V. Talanov a, M. Rajeswari b, J. Claassen c a
b
Neocera, Inc., 10000 Virginia Manor Road, Beltsville, MD 20705, USA Center for Superconductivity Research, University of Maryland, College Park, MD 20742, USA c Naval Research Laboratory, Washington, DC 20375, USA Received 16 October 2000; accepted 7 November 2000
Abstract High temperature superconducting (HTS) ®lms on ¯exible, low loss, low thermal conductivity substrates oer unique advantages to transmit multichannel digital data with low signal attenuation for cryoelectronic applications. Polycrystalline, ¯exible yttria stabilized zirconia (YSZ) with a low thermal conductivity of 0.015 W/cm K, a low RF loss of 4 10 4 (at 77 K, 5 GHz) and a relatively low dielectric constant of 28 is an excellent choice as a substrate if high quality HTS ®lms can be developed with desirable RF properties. This paper presents recent data obtained on biaxially textured Y1 B2 C3 O7 x (YBCO) ®lms deposited on polycrystalline YSZ substrates with a biaxially-textured YSZ template. YSZ structural templates were developed by Ion beam-assisted pulsed laser deposition (PLD). YBCO ®lms were deposited by PLD. The biaxially textured YBCO ®lms exhibit in-plane (Phi-scans) FWHMs of 7°. The transition temperatures (Tc 's) of the ®lms are in the range 88±89 K with transition widths of 0.5 K. The critical current densities (Jc 's) measured at 77 K, zero ®eld, are in the range of 2 106 A/cm2 . The surface resistance of the ®lms measured at 77 K, 10 GHz is 700 lX indicating a low microwave loss in these ®lms. The high materials quality obtained in these HTS ®lms on polycrystalline substrates can be used in fabricating a variety of components for cryoelectronic applications. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 74.25. q; 74.76. w Keywords: High temperature superconduction; Cryoelectronics; Biaxially textured
1. Introduction The low-surface resistance associated with hightemperature superconducting (HTS) ®lms on low
* Corresponding author. Tel.: +1-301-210-1010; fax: +1-301210-1042. E-mail address: [email protected] (K.S. Harshavardhan).
loss substrates facilitate large channels of digital data transmission with low signal attenuation. In several HTS cryoelectronic (4±80 K) applications, the choice of substrate is an important parameter to obtain optimum performance. Substrates with attributes such as a low thermal conductivity for thermal isolation, high ¯exural strength and high fracture toughness for ¯exibility, a low RF loss tangent for obtaining low signal attenuation in the stripline con®guration, a relatively low dielectric
0921-4534/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 1 ) 0 0 5 8 4 - 6
K.S. Harshavardhan et al. / Physica C 357±360 (2001) 1368±1372
constant for low cross-talk between the channels are quite desirable in these applications. Another very important consideration is that the substrate should have a good compatibility with respect to HTS ®lm growth, namely, a close thermal expansion coecient match with HTS ®lm and no chemical reaction between the ®lm and the substrate at the growth temperatures [1]. Polycrystalline yttria stabilized zirconia (YSZ) is a unique substrate material for developing low loss HTS transmission lines for cryoelectronic applications. YSZ has a low thermal conductivity of 0.015 W cm 1 K 1 , a low RF loss (tan d 4 10 4 at 5 GHz, 77 K) [2], a relatively low dielectric constant (r 28), and is compatible with Y1 B2 C3 O7 x (YBCO) ®lm growth requirements. Furthermore, this substrate is ¯exible with a bend radius approaching 1 cm, and high ¯exural strength of 1500 MPa. Epitaxial HTS ®lms deposited on single crystalline substrates in general exhibit optimum microwave performance. Films deposited on polycrystalline substrates will also be polycrystalline in nature and will consist of large angle grain boundaries. These grain boundaries act as weak links and contribute to undesirable and unacceptable microwave losses [3]. It is therefore mandatory to eliminate high angle ( P 10°) grain boundaries in these ®lms by innovative deposition schemes. In the present work, we signi®cantly eliminated the presence of undesirable high angle grain boundaries by ®rst depositing a biaxially aligned YSZ template by the ion-assisted pulsed laser deposition (PLD) method. The subsequently deposited YBCO ®lms are also biaxially aligned and exhibited desirable RF properties. This paper presents a summary of our experimental results.
Fig. 1. Growth schematic for biaxially aligned YBCO on polycrystalline YSZ substrate with IBAD in-plane textured template.
matic is shown in Fig. 1. In this growth approach, a CeO2 structural template was used to assist growth of predominantly c-axis oriented YBCO. Fig. 2 shows the deposition geometry. The assisting ion beam during ion beam-assisted deposition (IBAD) of YSZ was obtained from a 3 cm Kaufmann ion source, with 200 eV beam energy and 10 mA beam current. The background pressure for YSZ deposition was 7 10 4 Torr of a mixture of 100:1 argon and oxygen. YSZ ®lms were about 1 lm thick and the typical deposition rate was 0.1 A/pulse. YSZ was deposited at room temperature, with no intentional substrate heating. The substrate self-heated during deposition was of CeO2 50±70°C. After YSZ deposition, 100 A buer, and then 4000 A thick YBCO were subsequently deposited at 770°C in 300 mTorr of oxygen.
2. Experimental Polycrystalline YSZ with no preferred crystallographic orientation is used as the substrate in our experimental work. All ®lms were deposited by PLD. Biaxially aligned YSZ buer layers were developed by ion assisted PLD. The growth sche-
1369
Fig. 2. Schematic setup of ion beam assisted PLD.
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K.S. Harshavardhan et al. / Physica C 357±360 (2001) 1368±1372
3. Results and discussion 3.1. Structural evaluations ± four-circle X-ray diraction IBAD has recently emerged as an innovative deposition method to deposit in plane aligned structural templates on polycrystalline substrates. In this method an energetic ion beam from a standard Kaufmann ion source is directed towards the growing ®lm at an angle corresponding to the crystallographic direction of the ®lm. In all the cases reported, it has been found that selective growth of (0 0 1) YSZ for example, occurred over (1 1 1) or (1 1 0) YSZ orientations in the case of YSZ depositions. This is interpreted in the literature [4±6] as follows: An energetic beam striking the growing ®lm at an angle corresponding to the angle of a channeling direction for a particular crystalline orientation can enhance the growth in this orientation, while destroying grains growing in the other non-channeled orientations. The [1 1 1] channeling in cubic YSZ is 54:7° from the [0 0 1] direction, and as a result, ions directed near this angle to the substrate normal during growth will enhance the required (0 0 1) orientation through a preferential resputtering eect. Through this preferential growth and selective etching mechanism, it is possible to achieve a structurally in-plane aligned ®lm growth, which would be an excellent template for subsequent ®lm depositions, carried out at high temperatures. Fig. 3 shows the four-circle X-ray diraction Phi-scan data of the (1 0 3) re¯ections of the YBCO ®lm. The in-plane texture is shown in the Phi angle scan by the four peaks separated by 90°. The FWHMs are 7° indicating good in-plane texture. The remarkable feature of this data is that the polycrystalline YSZ substrate on which the YBCO ®lm is deposited is randomly oriented with no in-plane texture. Fig. 4 shows the four-circle X-ray diraction Uscan data of the entire multilayer heterostructure (YBCO/CeO2 /IBAD-YSZ/Poly-YSZ). Shown at the top are the (1 0 3) re¯ections of the YBCO ®lm (shown separately in Fig. 3 above). In this plot, /scan data are presented for the IBAD YSZ biaxial template (bottom of the plot) and CeO2 structural
Fig. 3. Four-circle X-ray diraction Phi-scan data showing the in-plane texture of YBCO on randomly oriented YSZ substrate.
Fig. 4. X-ray Phi-scan data of the entire multilayer heterostructure.
template (middle of the plot). The data are obtained from the (2 0 2) re¯ections in both the cases and the FWHMs in this case are 12±13° and 7±8° respectively. It may be mentioned here that texture development during ion-assisted YSZ ®lm growth is evolutionary with thickness [7,8], with the surface layers having a superior in-plane texture than the ®lm closer to the ®lm-substrate interface. The larger FWHMs seen in the case of YSZ ®lm are therefore a cumulative eect since our X-ray diffractometer cannot distinguish between surface and volume contributions. The FWHMs observed in the case of CeO2 (7±8°) are supportive of this view point that the YSZ surface has a superior inplane texture. Fig. 5 shows the rocking angle XRD data (Omega-scans) obtained from (0 0 5) YBCO. The
K.S. Harshavardhan et al. / Physica C 357±360 (2001) 1368±1372
1371
Fig. 5. Rocking angle (Omega-scans) data of (0 0 5) YBCO.
rocking angle FWHM of 1.5° is indicative of good out-of-plane texture along the c-axis. X-ray diraction scans obtained in the h±2h mode (not presented here) indicate that all the ®lms are c-axis oriented. The XRD measurements therefore establish an excellent biaxial texture (both in the abplane and along the c-axis) in the YBCO ®lms. 3.2. AC susceptibility The biaxially textured ®lms were evaluated for transition temperature (Tc ), transition width (DTc ) and critical current density (Jc ) by AC susceptibility measurements. The Tc 's measured for two representative ®lms were in the range 88±89 K with transition widths around 0.5 K. Fig. 6 shows data obtained from a representative YBCO sample. Critical current densities measured for these two representative ®lms at 77 K and zero ®eld were
Fig. 6. AC susceptibility data from a representative, biaxially aligned YBCO ®lm.
Fig. 7. Current density data for biaxially textured YBCO ®lms, obtained by AC susceptibility measurements.
1:5±2 106 A/cm2 at 77 K. Fig. 7 presents Jc data obtained from one of the YBCO ®lms. The Tc 's and Jc 's measured are both representative of a good YBCO ®lm quality needed for several device applications. The magnetic penetration depth measurements were carried out over a wide temperature range (5± 87 K) and are presented in Fig. 8. The penetration depth (k) measured at 77 K is 284 nm indicating excellent electromagnetic properties in the present biaxially textured YBCO ®lms. The microwave properties of the ®lms were evaluated by measuring the surface resistance (Rs ) of the ®lms. Rs was measured by a parallel plate resonator (PPR) technique (Fig. 9). The details of this technique were published elsewhere [9].
Fig. 8. Penetration depth data of biaxially textured YBCO ®lms.
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Fig. 9. Experimental geometry for PPR measurements.
Brie¯y, these measurements were carried out using two nominally identical thin ®lms. The ®lms were brought together, face-to-face, sandwiching a thin Te¯on dielectric (typically 12:5 lm thick). This combination forms a two-conductor parallel plate transmission line which can carry a quasi-TEM electromagnetic wave. This transmission line can be made resonant under special conditions and from the Q-factor of the PPR, the surface resistance can be calculated. At 10 GHz, 77K, we obtained surface resistance (Rs ) values of 700 lX for the biaxially aligned YBCO ®lms. It may be mentioned that epitaxial YBCO ®lms deposited on single crystalline substrates and measured with the same PPR technique typically exhibit Rs values in the range of 400±500 lX at 10 GHz, 77 K. It is therefore noteworthy that the Rs values obtained in the present case are among the best reported for YBCO on any polycrystalline substrate so far. The measured microwave properties also validate the possibility of fabricating a variety of low loss components using this unique materials technology. Our future work would involve design, fabrication and testing of a multi-channel cable employing the current materials base. The results of this eort will be published separately. 4. Conclusions Biaxially textured YBCO ®lms were developed on ¯exible, polycrystalline YSZ substrates using an in-plane aligned YSZ template. The in-plane FWHM of YBCO ®lms are about 7° as seen by X-
ray Phi-scans. The ®lms exhibit transition temperatures of the order of 88±89 K with transition widths of 0.5 K. The critical current densities measured at 77 K are in the range of 1:5±2 106 A/cm2 . The surface resistance of the ®lms measured at 10 GHz, 77 K, is 700 lX indicating an excellent potential of these ®lms in RF applications. The HTS ®lm quality in conjunction with a low thermal conductivity (0.015 W cm 1 K 1 ), low loss and ¯exible YSZ substrate forms a unique material base for a variety of cryoelectronic applications.
Acknowledgements This work was supported by the ONR grant N00014-98-M-0016.
References [1] Z.Y. Shen, The Future: High Temperature Superconducting Microwave Circuits, Artech House, Norwood, MA, 1994, p. 257. [2] T. Konaka, et al., J. Supercond. 4 (1991) 283. [3] N. Newman, W.G. Lyons, J. Supercond. 6 (3) (1993) 119. [4] Y. Iijima, et al., Appl. Phys. Lett. 60 (1992) 769. [5] R.P. Reade, et al., Appl. Phys. Lett. 61 (1992) 2231. [6] X.D. Wu, et al., Appl. Phys. Lett. 67 (1995) 2397. [7] N. Sonnenberg, A.S. Longo, M.J. Cima, B.P. Chang, K.G. Ressler, P.C. McIntyre, Y.P. Liu, J. Appl. Phys. 74 (1993) 1027. [8] X.D. Wu, S.R. Foltyn, P. Arendt, J. Townsend, C. Adams, I.H. Campbell, P. Tiwari, Y. Coulter, D.E. Peterson, Appl. Phys. Lett. 65 (1994) 1961. [9] R.C. Taber, Rev. Sci. Instrum. 61 (1990) 2200.
www.elsevier.com/locate/physc
High temperature superconducting ®lms on ¯exible substrates for cryoelectronics K.S. Harshavardhan a,*, H. Christen a, S.D. Silliman a, V. Talanov a, M. Rajeswari b, J. Claassen c a
b
Neocera, Inc., 10000 Virginia Manor Road, Beltsville, MD 20705, USA Center for Superconductivity Research, University of Maryland, College Park, MD 20742, USA c Naval Research Laboratory, Washington, DC 20375, USA Received 16 October 2000; accepted 7 November 2000
Abstract High temperature superconducting (HTS) ®lms on ¯exible, low loss, low thermal conductivity substrates oer unique advantages to transmit multichannel digital data with low signal attenuation for cryoelectronic applications. Polycrystalline, ¯exible yttria stabilized zirconia (YSZ) with a low thermal conductivity of 0.015 W/cm K, a low RF loss of 4 10 4 (at 77 K, 5 GHz) and a relatively low dielectric constant of 28 is an excellent choice as a substrate if high quality HTS ®lms can be developed with desirable RF properties. This paper presents recent data obtained on biaxially textured Y1 B2 C3 O7 x (YBCO) ®lms deposited on polycrystalline YSZ substrates with a biaxially-textured YSZ template. YSZ structural templates were developed by Ion beam-assisted pulsed laser deposition (PLD). YBCO ®lms were deposited by PLD. The biaxially textured YBCO ®lms exhibit in-plane (Phi-scans) FWHMs of 7°. The transition temperatures (Tc 's) of the ®lms are in the range 88±89 K with transition widths of 0.5 K. The critical current densities (Jc 's) measured at 77 K, zero ®eld, are in the range of 2 106 A/cm2 . The surface resistance of the ®lms measured at 77 K, 10 GHz is 700 lX indicating a low microwave loss in these ®lms. The high materials quality obtained in these HTS ®lms on polycrystalline substrates can be used in fabricating a variety of components for cryoelectronic applications. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 74.25. q; 74.76. w Keywords: High temperature superconduction; Cryoelectronics; Biaxially textured
1. Introduction The low-surface resistance associated with hightemperature superconducting (HTS) ®lms on low
* Corresponding author. Tel.: +1-301-210-1010; fax: +1-301210-1042. E-mail address: [email protected] (K.S. Harshavardhan).
loss substrates facilitate large channels of digital data transmission with low signal attenuation. In several HTS cryoelectronic (4±80 K) applications, the choice of substrate is an important parameter to obtain optimum performance. Substrates with attributes such as a low thermal conductivity for thermal isolation, high ¯exural strength and high fracture toughness for ¯exibility, a low RF loss tangent for obtaining low signal attenuation in the stripline con®guration, a relatively low dielectric
0921-4534/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 1 ) 0 0 5 8 4 - 6
K.S. Harshavardhan et al. / Physica C 357±360 (2001) 1368±1372
constant for low cross-talk between the channels are quite desirable in these applications. Another very important consideration is that the substrate should have a good compatibility with respect to HTS ®lm growth, namely, a close thermal expansion coecient match with HTS ®lm and no chemical reaction between the ®lm and the substrate at the growth temperatures [1]. Polycrystalline yttria stabilized zirconia (YSZ) is a unique substrate material for developing low loss HTS transmission lines for cryoelectronic applications. YSZ has a low thermal conductivity of 0.015 W cm 1 K 1 , a low RF loss (tan d 4 10 4 at 5 GHz, 77 K) [2], a relatively low dielectric constant (r 28), and is compatible with Y1 B2 C3 O7 x (YBCO) ®lm growth requirements. Furthermore, this substrate is ¯exible with a bend radius approaching 1 cm, and high ¯exural strength of 1500 MPa. Epitaxial HTS ®lms deposited on single crystalline substrates in general exhibit optimum microwave performance. Films deposited on polycrystalline substrates will also be polycrystalline in nature and will consist of large angle grain boundaries. These grain boundaries act as weak links and contribute to undesirable and unacceptable microwave losses [3]. It is therefore mandatory to eliminate high angle ( P 10°) grain boundaries in these ®lms by innovative deposition schemes. In the present work, we signi®cantly eliminated the presence of undesirable high angle grain boundaries by ®rst depositing a biaxially aligned YSZ template by the ion-assisted pulsed laser deposition (PLD) method. The subsequently deposited YBCO ®lms are also biaxially aligned and exhibited desirable RF properties. This paper presents a summary of our experimental results.
Fig. 1. Growth schematic for biaxially aligned YBCO on polycrystalline YSZ substrate with IBAD in-plane textured template.
matic is shown in Fig. 1. In this growth approach, a CeO2 structural template was used to assist growth of predominantly c-axis oriented YBCO. Fig. 2 shows the deposition geometry. The assisting ion beam during ion beam-assisted deposition (IBAD) of YSZ was obtained from a 3 cm Kaufmann ion source, with 200 eV beam energy and 10 mA beam current. The background pressure for YSZ deposition was 7 10 4 Torr of a mixture of 100:1 argon and oxygen. YSZ ®lms were about 1 lm thick and the typical deposition rate was 0.1 A/pulse. YSZ was deposited at room temperature, with no intentional substrate heating. The substrate self-heated during deposition was of CeO2 50±70°C. After YSZ deposition, 100 A buer, and then 4000 A thick YBCO were subsequently deposited at 770°C in 300 mTorr of oxygen.
2. Experimental Polycrystalline YSZ with no preferred crystallographic orientation is used as the substrate in our experimental work. All ®lms were deposited by PLD. Biaxially aligned YSZ buer layers were developed by ion assisted PLD. The growth sche-
1369
Fig. 2. Schematic setup of ion beam assisted PLD.
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K.S. Harshavardhan et al. / Physica C 357±360 (2001) 1368±1372
3. Results and discussion 3.1. Structural evaluations ± four-circle X-ray diraction IBAD has recently emerged as an innovative deposition method to deposit in plane aligned structural templates on polycrystalline substrates. In this method an energetic ion beam from a standard Kaufmann ion source is directed towards the growing ®lm at an angle corresponding to the crystallographic direction of the ®lm. In all the cases reported, it has been found that selective growth of (0 0 1) YSZ for example, occurred over (1 1 1) or (1 1 0) YSZ orientations in the case of YSZ depositions. This is interpreted in the literature [4±6] as follows: An energetic beam striking the growing ®lm at an angle corresponding to the angle of a channeling direction for a particular crystalline orientation can enhance the growth in this orientation, while destroying grains growing in the other non-channeled orientations. The [1 1 1] channeling in cubic YSZ is 54:7° from the [0 0 1] direction, and as a result, ions directed near this angle to the substrate normal during growth will enhance the required (0 0 1) orientation through a preferential resputtering eect. Through this preferential growth and selective etching mechanism, it is possible to achieve a structurally in-plane aligned ®lm growth, which would be an excellent template for subsequent ®lm depositions, carried out at high temperatures. Fig. 3 shows the four-circle X-ray diraction Phi-scan data of the (1 0 3) re¯ections of the YBCO ®lm. The in-plane texture is shown in the Phi angle scan by the four peaks separated by 90°. The FWHMs are 7° indicating good in-plane texture. The remarkable feature of this data is that the polycrystalline YSZ substrate on which the YBCO ®lm is deposited is randomly oriented with no in-plane texture. Fig. 4 shows the four-circle X-ray diraction Uscan data of the entire multilayer heterostructure (YBCO/CeO2 /IBAD-YSZ/Poly-YSZ). Shown at the top are the (1 0 3) re¯ections of the YBCO ®lm (shown separately in Fig. 3 above). In this plot, /scan data are presented for the IBAD YSZ biaxial template (bottom of the plot) and CeO2 structural
Fig. 3. Four-circle X-ray diraction Phi-scan data showing the in-plane texture of YBCO on randomly oriented YSZ substrate.
Fig. 4. X-ray Phi-scan data of the entire multilayer heterostructure.
template (middle of the plot). The data are obtained from the (2 0 2) re¯ections in both the cases and the FWHMs in this case are 12±13° and 7±8° respectively. It may be mentioned here that texture development during ion-assisted YSZ ®lm growth is evolutionary with thickness [7,8], with the surface layers having a superior in-plane texture than the ®lm closer to the ®lm-substrate interface. The larger FWHMs seen in the case of YSZ ®lm are therefore a cumulative eect since our X-ray diffractometer cannot distinguish between surface and volume contributions. The FWHMs observed in the case of CeO2 (7±8°) are supportive of this view point that the YSZ surface has a superior inplane texture. Fig. 5 shows the rocking angle XRD data (Omega-scans) obtained from (0 0 5) YBCO. The
K.S. Harshavardhan et al. / Physica C 357±360 (2001) 1368±1372
1371
Fig. 5. Rocking angle (Omega-scans) data of (0 0 5) YBCO.
rocking angle FWHM of 1.5° is indicative of good out-of-plane texture along the c-axis. X-ray diraction scans obtained in the h±2h mode (not presented here) indicate that all the ®lms are c-axis oriented. The XRD measurements therefore establish an excellent biaxial texture (both in the abplane and along the c-axis) in the YBCO ®lms. 3.2. AC susceptibility The biaxially textured ®lms were evaluated for transition temperature (Tc ), transition width (DTc ) and critical current density (Jc ) by AC susceptibility measurements. The Tc 's measured for two representative ®lms were in the range 88±89 K with transition widths around 0.5 K. Fig. 6 shows data obtained from a representative YBCO sample. Critical current densities measured for these two representative ®lms at 77 K and zero ®eld were
Fig. 6. AC susceptibility data from a representative, biaxially aligned YBCO ®lm.
Fig. 7. Current density data for biaxially textured YBCO ®lms, obtained by AC susceptibility measurements.
1:5±2 106 A/cm2 at 77 K. Fig. 7 presents Jc data obtained from one of the YBCO ®lms. The Tc 's and Jc 's measured are both representative of a good YBCO ®lm quality needed for several device applications. The magnetic penetration depth measurements were carried out over a wide temperature range (5± 87 K) and are presented in Fig. 8. The penetration depth (k) measured at 77 K is 284 nm indicating excellent electromagnetic properties in the present biaxially textured YBCO ®lms. The microwave properties of the ®lms were evaluated by measuring the surface resistance (Rs ) of the ®lms. Rs was measured by a parallel plate resonator (PPR) technique (Fig. 9). The details of this technique were published elsewhere [9].
Fig. 8. Penetration depth data of biaxially textured YBCO ®lms.
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K.S. Harshavardhan et al. / Physica C 357±360 (2001) 1368±1372
Fig. 9. Experimental geometry for PPR measurements.
Brie¯y, these measurements were carried out using two nominally identical thin ®lms. The ®lms were brought together, face-to-face, sandwiching a thin Te¯on dielectric (typically 12:5 lm thick). This combination forms a two-conductor parallel plate transmission line which can carry a quasi-TEM electromagnetic wave. This transmission line can be made resonant under special conditions and from the Q-factor of the PPR, the surface resistance can be calculated. At 10 GHz, 77K, we obtained surface resistance (Rs ) values of 700 lX for the biaxially aligned YBCO ®lms. It may be mentioned that epitaxial YBCO ®lms deposited on single crystalline substrates and measured with the same PPR technique typically exhibit Rs values in the range of 400±500 lX at 10 GHz, 77 K. It is therefore noteworthy that the Rs values obtained in the present case are among the best reported for YBCO on any polycrystalline substrate so far. The measured microwave properties also validate the possibility of fabricating a variety of low loss components using this unique materials technology. Our future work would involve design, fabrication and testing of a multi-channel cable employing the current materials base. The results of this eort will be published separately. 4. Conclusions Biaxially textured YBCO ®lms were developed on ¯exible, polycrystalline YSZ substrates using an in-plane aligned YSZ template. The in-plane FWHM of YBCO ®lms are about 7° as seen by X-
ray Phi-scans. The ®lms exhibit transition temperatures of the order of 88±89 K with transition widths of 0.5 K. The critical current densities measured at 77 K are in the range of 1:5±2 106 A/cm2 . The surface resistance of the ®lms measured at 10 GHz, 77 K, is 700 lX indicating an excellent potential of these ®lms in RF applications. The HTS ®lm quality in conjunction with a low thermal conductivity (0.015 W cm 1 K 1 ), low loss and ¯exible YSZ substrate forms a unique material base for a variety of cryoelectronic applications.
Acknowledgements This work was supported by the ONR grant N00014-98-M-0016.
References [1] Z.Y. Shen, The Future: High Temperature Superconducting Microwave Circuits, Artech House, Norwood, MA, 1994, p. 257. [2] T. Konaka, et al., J. Supercond. 4 (1991) 283. [3] N. Newman, W.G. Lyons, J. Supercond. 6 (3) (1993) 119. [4] Y. Iijima, et al., Appl. Phys. Lett. 60 (1992) 769. [5] R.P. Reade, et al., Appl. Phys. Lett. 61 (1992) 2231. [6] X.D. Wu, et al., Appl. Phys. Lett. 67 (1995) 2397. [7] N. Sonnenberg, A.S. Longo, M.J. Cima, B.P. Chang, K.G. Ressler, P.C. McIntyre, Y.P. Liu, J. Appl. Phys. 74 (1993) 1027. [8] X.D. Wu, S.R. Foltyn, P. Arendt, J. Townsend, C. Adams, I.H. Campbell, P. Tiwari, Y. Coulter, D.E. Peterson, Appl. Phys. Lett. 65 (1994) 1961. [9] R.C. Taber, Rev. Sci. Instrum. 61 (1990) 2200.