Measurements of the Surface Resistance of Hts Thin Films From 0.5 to 40Ghz
- PDF / 644,440 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 13 Downloads / 189 Views
MEASUREMENTS OF THE SURFACE RESISTANCE OF HTS THIN FILMS FROM 0.5 TO 40GIIz J. STEINBECKt, D.E. OATES-, AND A.C. ANDERSON*
tRADC/EEAC, Hlanscom AFB, MA 01731 "Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02173 ABSTRACT We have measured the surface resistance R, in polycrystalline films of YB.CO and BSCCO. deposited in our laboratory as well as oriented films made by other laboratories by codepostion techniques. The R, of YBCO and BSCCO has been measured in the frequency range between 0.5 and 40 GhI using a stripline resonator technique. R, for the filns is negirly proportional to the square of the applied frequency over the entire measurement range. Thlie magnitude of R, is, however, strongly dependent on the film microstructure. Our measurements at 1 GIz and 4 K show that randomly oriented films have R, - 10-'fi (close to Cu) while oriented large-grain films have markedly lower R, - 2 x 10" f0, approaching the 11,of superconducting Nb. The magnitude of R, rises to - 2 fQand - 10-'f at 40 Glz for the randomly oriented and preferentially oriented films, respectively. An effective penetration depth, Aefj, has been determined from R, using local electrodynamics. We find that AJj is dependent on film mficrostructure and is - 5 pm for high-l4 films, decreasing to - 5000 A for low-R, filnis. The smaller values of A,/! calculated for oriented films are of similar magnitude to values of the YBCO penetration depth (- 2000 A) reported in the literature. The use of the stripline resonator technique for temperature and magnetic field dependent ,w.tsurements of R, will also be discussed. INTRODUCTION Low-T, materials such as Nb and Pb have already demonstrated that superconducting electronics provide significant performance enhancements in analog circuits. The primary advantage of using high temperature superconductors in electronics is the substantially lower cryogenic costs than low-'r, superconductors. Wide use of the cuprate superconductors in electronics depends, however, on the ability to make large-area, low-loss films on suit.Lble substrates. The surface resistance R, is a measure of the ac losses. Several techniques have been employed to measure R, of the copper-oxide superconductors. Traditional cavity techniques have been used by many investigators [1,4] to measure the temperature dependence of R, of thin films of the cuprates at a single frequency. Microwave transmissiomi [5] has also been used to measure the R. of YBCO thin films, but the data analysis is complicated. The stripline-resonator technique uses films which are sized appropriately for electronic applications and maintains the ability to measure R, at frequencies which are of technological interest (< 10 GHz). The stripline resonator can also be used to measure the temperature and magnetic-field dependence of R, and maintain high sensitivity by constructing aimall-high-T, resonator. EXPERIMENTAL The superconducting-stripline-resonator technique utilizes a section of symmetric, planar transmission line into which microwave powe
Data Loading...
