Correlations Between YBa₂Cu₃O_7-δ Thin Film Materials Properties and RF Device Performance

Abstract

Better knowledge of the relationships between YBa2Cu307-δ (YBCO) materials properties and the RF performance of devices made from these materials should lead to improved device performance and yields. A variety of materials tests were performed on our production YBCO films which were patterned into standard microstrip resonators. The materials parameters were then compared with the unloaded Q of the resonators at 77 K. As expected, films with higher Q's tended to have higher Tc, higher Jc, greater film thickness, and better crystallinity. The last was based on narrower YBCO rocking curve peak, lower second phase density (judged by lower resistivity and greater θ-2θ (005) peak area), and a narrower θ-2θ (005) peak. The room temperature sheet resistance was found to be a useful predictor of microwave performance for films that are otherwise similar.

Microstructure and microwave surface resistance of typical YBaCuO thin films on sapphire and LaAlO3

“…The presence of a-axis-oriented grains was found to lower j c , as shown in figure 8. Furthermore, the critical current density j c was stated to anticorrelate with R s in many cases [9,37]. However, an enhancement of R s due to a-axisoriented grains was not evident in the present study, probably due to other sources of microwave losses which varied from wafer to wafer.…”

“…Also, tilt of the c axis and other crystallographic imperfections, revealed from the XRD (005) peak in terms of the FWHM (full width at half maximum, ) of rocking curves and of -2 scans, may influence R s very sensitively: an about ten-fold increase of R s between = 0.2 • and 0.7 • was reported in [1] for pulsed-laser-deposited (PLD) YBCO films on various substrates. A corresponding decrease of the unloaded quality factor of YBCO resonators was stated in [9]. Moreover, R s was observed to decrease by about a factor of 10 as the orthorhombic splitting b − a increased from 4 to 6 × 10 −3 nm in otherwise quite perfect and non-oxygendeficient magnetron-sputtered YBCO films on LaAlO 3 [3].…”

“…There should be no effect of the a-axis oriented grains, since lower R s is observed in figure 9(b) at a much higher a fraction. The XRD (005) rocking curve of this sample revealed a relatively large FWHM of 0.7 • which was reported to anticorrelate with R s [9]. However, the film contained large outgrowths, up to 1 µm in size, which are supposed to enhance R s [10].…”

Microstructure and microwave surface resistance of YBaCuO thin films

“…Therefore studies of microstructure effects on the surface resistance R of c-oriented YBa2Cu307-x (YBCO) films were performed for two cases: (i) YBCO laser-deposited (PLD) on both sides of 73 mm diameter sapphire substrates [l], to be used for lowpower microstrip resonators and C-band bandpass filters, and (ii) YBCO deposited by planar DC sputtering on 50 mm LaA103 substrates [2]. Since R is known to be affected by various parameters in a complex way [3], it remains difficult to obtain unique relationships by comparing various experimental runs and wafers. Therefore alterations of film properties along the radius of a given wafer were also examined.…”