Narrow YBa2Cu3O7-δ Coplanar Transmission Lines for Reentrant Delay Line Memory Application

Wataru HATTORI  Tsutomu YOSHITAKE  Shuichi TAHARA  

IEICE TRANSACTIONS on Electronics   Vol.E81-C    No.10    pp.1557-1564
Publication Date: 1998/10/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section INVITED PAPER (Special Issue on Low- and High-Temperature Superconductive Electron Devices and Their Applications)
Category: High-Frequency Properties of Thin Films
YBa2Cu3O7-δ (YBCO),  reentrant delay line memory,  coplanar transmission line,  

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Reentrant delay line memories using narrow YBa2Cu3O7-δ (YBCO) coplanar transmission lines are proposed. The proposed memory is composed of a looped YBCO coplanar delay line and a 22 semiconductor crossbar switch. This type of memory is superior to semiconductor memories in operating speed, the number of logic gates, power dissipation, and so on. We have also developed narrow and low-loss YBCO coplanar transmission lines for use in these reentrant delay line memories. Etch-back planarization and a patterning process combining Ar-ion milling and wet-etching enabled us to fabricate 18-cm-long YBCO coplanar transmission lines as narrow as 5 µm, and these lines did not suffer from electrical shorts even when the spacing was only 2. 5 µm. The surface resistances calculated from the attenuation constants of 5-, 10-, and 25-µm-wide lines provide similar low values of 0. 18-0. 26 mΩ at 10 GHz and 55 K. This indicates that the process damage was sufficiently suppressed despite the narrow line widths. The 5-µm-wide line attained a low attenuation constant of 2. 7 dB/m, which is similar to that in Cu coaxial cables. Even in the 5-µm-wide line, no significant increase in transmission loss was observed up to an input power level of 16 mW at 10 GHz and 55 K. This input power is comparable to that required to propagate digital signals from semiconductor circuits. Therefore high-speed digital signals can propagate through these narrow YBCO coplanar lines without significant attenuation of the signal pulses. Thus, these narrow YBCO coplanar lines can be used in the reentrant delay line memories.