Browsing by Author "Schilling, M."

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Open Access
1/f Noise characteristics of SEJ Y-Ba-Cu-O Rf-SQUIDs on LaAlO3 substrate and the step structure, film, and temperature dependence
(IEEE, 2001-03) Fardmanesh, M.; Schubert, J.; Akram, R.; Bick, M.; Zhang, Y.; Banzet, M.; Zander, W.; Krause, H. J.; Burkhart, H.; Schilling, M.
Step edge junction (SEJ) rf-SQUID magnetometers and gradiometers were fabricated using PLD Y-Ea-Cu-0 films on LaA10,(100) and SrTi0,(100) substrates. Effects of different step structure and the film properties on the yield, optimal operating temperature, and the l/f noise of the SQUIDs were investigated. The step structure was controlled using various IBE processes. The devices on LaAIO, showed higher sensitivity to the step structure compared to those on SrTiO,. This was due to re-deposition of substrate material at the steps prepared using the conventional IBE process resulting in a very low yield of unstable SQUIDs. High yield of low l/f noise stable SQUIDs was obtained on LaAIO, substrates with sharp steps prepared using an optimized IBE process. A typical l/f noise corner frequency of about lOHz at 77K with two major temperature dependencies was obtained. The temperature dependencies of the l/f noise could be correlated to the junction and the film of washer area of the SQUIDS. The white noise of our devices showed a dependency mainly on the amplitude of the flux to voltage transfer function signal. The operating temperature range of the SQUIDs could be controlled by the step structure and narrowed when the optimal operating temperature range was increased. All the measured junctions of our devices on the modified steps showed RSJ type behavior with a moderate decrease of the R, versus temperature.
Open Access
Dependence of the substrate structure and the film growth at the junction of YBCO SEJ rf-SQUIDs on the IBE process and effects on the SQUID's characteristics
(Elsevier, 2002) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Banzet, M.; Zander, W.; Zhang, Y.; Schilling, M.; Krause, H-J.
Step edge junction (SEJ) rf-SQUIDs were made of 200 nm thick YBCO films on LaAlO3(100) substrates using pulsed laser deposition technique. The steps on the substrates were developed using a combination of stationary and rotating angled argon ion beams with different beam energies and intensities. While sharp clean steps with heights up to 300 nm were obtained on the substrates using the combinatorial ion beam etching (IBE) process, very shallow ramp-type surfaces were found developing on the bottom of the trench, close to the steps. The ramp-type surfaces were found to be a source of hole-type defects in the films grown at the step edges. High quality films could be obtained on the flat regions away from the steps. Higher defect densities in the films close to the SEJs resulted in devices with higher 1/f noise and wider spread of the junction parameters. The 1/f noise of such devices increased with decreasing temperature. High quality films on sharp clean steps with flat substrate surfaces, developed using optimized combinatorial IBE process, resulted in higher yield of low 1/f noise SQUIDs. The Ic of the junctions and hence the working temperature of the SQUID could also be controlled by the junction width and the step height.