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Simulation of surface resistance of high temperature YBa2Cu3O7 multilayers for multichip modules
PAYSlCA
Physica C 235 240 (1994)3367 3368 North-Holland
Simulation of Surface Resistance of High Temperature YBa2Cu307 Multilayers for Multichip Modules Janina E. Ceremuga and Gregory H. Allen James Cook University of North Queensland, Department of Electrical and Computer Engineering, Townsville, Q4811, Australia The influence of insulating layers on surface impedance of multilayer YBCO structures for MCMs has been simulated and compared with measurement results of Missert [3]. It has been found that a lossy dielectric layer of high ¢r of thickness up to 0.5~tm has negligible influence on the effective surface resistance and reactance of YBa2Cu307 tri- and pentalayers. 1. INTRODUCTION One of potential applications of High Temperature Superconducting multilayers is in Multichip Modules (MCMs) [1]. MCMs provide multilevel computer interconnections enabling significant reduction of delay time as compared to conventional planar systems (eg. IBM3081- 26ns, IBM3033 - 57ns). Substitution of HTS materials for metallic conductors can allow for an increase of interconnector density of MCMs. This will result in reduction of the required numbers of layers and the increase of chip-to-chip data rates leading to further decrease of the overall delay time of systems. The superconducting multilayer proposed for MCM (under development at several organisations) is shown in Fig. I after [2]. r~
To provide good insulation between the HTS power plane and the HTS ground plane a dielectric of high relative permittivity should be used. SrTiO 3 is a possible choice although it exhibits significant losses at high frequencies. Hence its thickness should be small. On the other hand uniform and full coverage has to be ensured. The question arises "how thick can the high er dielectric layer be before it significantly affects propagation properties of HTS multilayers at high frequencies?". To answer this question we have calculated the surface impedance of the MCM structure of Fig. 1 with the YBa2Cu307 superconductor for different thickness of the SrTiO3 layer. We have also simulated trilayer structures YBCO/CeO2/ SrTiO3/YBCO on LaA103 grown by Missert et al and compared our calculations with measurement results of [3]. 2. S I M U L A T I O N OF YBCO M U L T I L A Y E R S
hi~
Fig. 1. Schematic diagram of a HTS MCM [2]. The structure contains HTS layers, low loss low er and high ¢r insulating layers and vias.
Calculations of surface resistance and reactance (Rs and Xs) have been done employing the transmission line analogy to describe properties of materials as in [4] and using MATLAB software [5]. As the clock frequency of computer systems approaches microwave range we have simulated the multilayers at 500MHz and 10GHz at 77K. We have assumed typical values for YBa2Cu307 material: the bulk Rs of 1 IJ~ and 400 gfa
0921-4534/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)02249-6
J.E. Ceremuga, G.tt. Allen/Pt~vsica C 235 240 (1994) 3367 3368
3368
respectively and the penetration depth of X of 0.45~tm at 77K. Simulation results for the structure of Fig. 1 are presented in Fig. 2. Thickness of the YBCO layer of 0.5tam, CeO2 as the low £r dielectric and 0.5mm thick LaA10 3 substrate have been assumed in the calculations.
TABLE 2. Variation of simulated Zseff for different CeO2 and STO thickness. CeO2 nm 200 70 0
LaAIO/YBCO/SrTiO/YBCO/CeO/YBCO 100 .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
STO nm 0 130 200
Rseff ~tf2 569.288 569.294 569.298
Xseff m£2 52.9742 52.9744 52.9745
LaAIO3/YBCO /SrTiO3/CeO2 /YBCO 100
.
(/)
co. 10 .2 °e 10.2 ~
O
.- . . - 1" micron YBCO
i
.~_
10GHzl
12-
rr 10 "~ 0.5GHz
10-4 Relative change in Rseff 10 .2
10-'
10 °
101
Thickness of SrTi03 in microns
10 -~
0
500 1000 Thickness of SrTiO3 in microns
Fig. 2 Simulated influence of STO on Rseff of the MCM structure for 0.5pm and l~tm YBCO.
Fig. 4. Influence of STO on Rseff.
Simulation results for the YBCO/CeO2/ SrTiO3/YBCO on LaAIO3 structure described in [3] are summarised below for 200nm YBCO.
3. CONCLUSIONS
TABLE 1. Rseff for the structure of films' thickness 200nm, 70nm, 130nm, 200nm, 0.5ram. Rseff in ~t£2after [3] T=4K T=77K 60 appr. 600
Simulated Rseff in pfl T=77K appr. 569
LaAIO3/YBCO/SrTiO3/CeO2/YBCO, 10GHz 200
Simulations of high frequency properties of YBCO multilayers have shown that high loss high £r dielectric of thickness up to l~tm can increase the effective impedance of YBCO films 0.5~tm thick only by few %. For l~tm thick YBCO influence of STO on the signal layers is completely nulled by the power plane. Hence it is feasible to use SrTiO3 to improve isolation between YBCO planes in HTS multilayer electronic circuits as suggested in [3] without increase of losses.
Acknowledgements: this work has been done under the research grant ARC Small 149782 (James Cook University of North Queensland). ~
o
REFERENCES
-100 -200 0
100
200
300
400
R(x) Fig.3 Impedance along the structure in form of Smith Chart
1. U. Goshal, T. Van Duzer, IEEE MCM-92 175. 2. Boo J.L. Nielsson, SPIE Vol. 2156 (1994) 107. 3. N. Missert et al, IEEE Trans. Appl. Sup. No.1 (1993) 1741. 4. J.E. Ceremuga and G.H. Allen, ISEC'93 28. 5. MATLAB Users Guide, Math Works (1989).
Physica C 235 240 (1994)3367 3368 North-Holland
Simulation of Surface Resistance of High Temperature YBa2Cu307 Multilayers for Multichip Modules Janina E. Ceremuga and Gregory H. Allen James Cook University of North Queensland, Department of Electrical and Computer Engineering, Townsville, Q4811, Australia The influence of insulating layers on surface impedance of multilayer YBCO structures for MCMs has been simulated and compared with measurement results of Missert [3]. It has been found that a lossy dielectric layer of high ¢r of thickness up to 0.5~tm has negligible influence on the effective surface resistance and reactance of YBa2Cu307 tri- and pentalayers. 1. INTRODUCTION One of potential applications of High Temperature Superconducting multilayers is in Multichip Modules (MCMs) [1]. MCMs provide multilevel computer interconnections enabling significant reduction of delay time as compared to conventional planar systems (eg. IBM3081- 26ns, IBM3033 - 57ns). Substitution of HTS materials for metallic conductors can allow for an increase of interconnector density of MCMs. This will result in reduction of the required numbers of layers and the increase of chip-to-chip data rates leading to further decrease of the overall delay time of systems. The superconducting multilayer proposed for MCM (under development at several organisations) is shown in Fig. I after [2]. r~
To provide good insulation between the HTS power plane and the HTS ground plane a dielectric of high relative permittivity should be used. SrTiO 3 is a possible choice although it exhibits significant losses at high frequencies. Hence its thickness should be small. On the other hand uniform and full coverage has to be ensured. The question arises "how thick can the high er dielectric layer be before it significantly affects propagation properties of HTS multilayers at high frequencies?". To answer this question we have calculated the surface impedance of the MCM structure of Fig. 1 with the YBa2Cu307 superconductor for different thickness of the SrTiO3 layer. We have also simulated trilayer structures YBCO/CeO2/ SrTiO3/YBCO on LaA103 grown by Missert et al and compared our calculations with measurement results of [3]. 2. S I M U L A T I O N OF YBCO M U L T I L A Y E R S
hi~
Fig. 1. Schematic diagram of a HTS MCM [2]. The structure contains HTS layers, low loss low er and high ¢r insulating layers and vias.
Calculations of surface resistance and reactance (Rs and Xs) have been done employing the transmission line analogy to describe properties of materials as in [4] and using MATLAB software [5]. As the clock frequency of computer systems approaches microwave range we have simulated the multilayers at 500MHz and 10GHz at 77K. We have assumed typical values for YBa2Cu307 material: the bulk Rs of 1 IJ~ and 400 gfa
0921-4534/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)02249-6
J.E. Ceremuga, G.tt. Allen/Pt~vsica C 235 240 (1994) 3367 3368
3368
respectively and the penetration depth of X of 0.45~tm at 77K. Simulation results for the structure of Fig. 1 are presented in Fig. 2. Thickness of the YBCO layer of 0.5tam, CeO2 as the low £r dielectric and 0.5mm thick LaA10 3 substrate have been assumed in the calculations.
TABLE 2. Variation of simulated Zseff for different CeO2 and STO thickness. CeO2 nm 200 70 0
LaAIO/YBCO/SrTiO/YBCO/CeO/YBCO 100 .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
STO nm 0 130 200
Rseff ~tf2 569.288 569.294 569.298
Xseff m£2 52.9742 52.9744 52.9745
LaAIO3/YBCO /SrTiO3/CeO2 /YBCO 100
.
(/)
co. 10 .2 °e 10.2 ~
O
.- . . - 1" micron YBCO
i
.~_
10GHzl
12-
rr 10 "~ 0.5GHz
10-4 Relative change in Rseff 10 .2
10-'
10 °
101
Thickness of SrTi03 in microns
10 -~
0
500 1000 Thickness of SrTiO3 in microns
Fig. 2 Simulated influence of STO on Rseff of the MCM structure for 0.5pm and l~tm YBCO.
Fig. 4. Influence of STO on Rseff.
Simulation results for the YBCO/CeO2/ SrTiO3/YBCO on LaAIO3 structure described in [3] are summarised below for 200nm YBCO.
3. CONCLUSIONS
TABLE 1. Rseff for the structure of films' thickness 200nm, 70nm, 130nm, 200nm, 0.5ram. Rseff in ~t£2after [3] T=4K T=77K 60 appr. 600
Simulated Rseff in pfl T=77K appr. 569
LaAIO3/YBCO/SrTiO3/CeO2/YBCO, 10GHz 200
Simulations of high frequency properties of YBCO multilayers have shown that high loss high £r dielectric of thickness up to l~tm can increase the effective impedance of YBCO films 0.5~tm thick only by few %. For l~tm thick YBCO influence of STO on the signal layers is completely nulled by the power plane. Hence it is feasible to use SrTiO3 to improve isolation between YBCO planes in HTS multilayer electronic circuits as suggested in [3] without increase of losses.
Acknowledgements: this work has been done under the research grant ARC Small 149782 (James Cook University of North Queensland). ~
o
REFERENCES
-100 -200 0
100
200
300
400
R(x) Fig.3 Impedance along the structure in form of Smith Chart
1. U. Goshal, T. Van Duzer, IEEE MCM-92 175. 2. Boo J.L. Nielsson, SPIE Vol. 2156 (1994) 107. 3. N. Missert et al, IEEE Trans. Appl. Sup. No.1 (1993) 1741. 4. J.E. Ceremuga and G.H. Allen, ISEC'93 28. 5. MATLAB Users Guide, Math Works (1989).