NARROW YBA2CU3O7-DELTA COPLANAR TRANSMISSION-LINES FOR REENTRANT DELAY-LINE MEMORY APPLICATION

Reentrant delay line memories using narrow YBa2Cu3O7-delta (YBCO) copl anar transmission lines are proposed. The proposed memory is composed of a looped YBCO coplanar delay line and a 2 X 2 semiconductor crossba r 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 transmis sion lines for use in these reentrant delay line memories. Etch-back p lanarization 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 mu m, and these lines did not suffer from electr ical shorts even when the spacing was only 2.5 mu m. The surface resis tances calculated from the attenuation constants of 5- 10-, and 25-mu m-wide lines provide similar low values of 0.18 -0.26 m Ohm at 10 GHz and 55 K. This indicates that the process damage was sufficiently supp ressed despite the narrow line widths. The 5-mu m-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-mu m-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 coplana r lines without significant attenuation of the signal pulses. Thus, th ese narrow YBCO coplanar lines can be used in the reentrant delay line memories.