Pulsed Laser Deposition of High T c Superconducting Thin Films for Electronic Device Applications
- PDF / 2,421,813 Bytes
- 7 Pages / 576 x 777.6 pts Page_size
- 103 Downloads / 217 Views
multicomponent ceramic oxide materials.4* The success of the PLD technique for HTS is due, partly, to the ease with which stoichiometric thin films could be deposited in a high-pressure oxygen ambient. In this article, we will demonstrate how PLD has
Figure 1. Five-pole modified Chebyschev parallel-coupled-line bandpass filter. This filter is implemented in microstrip at x-band (10 GHz frequency range) and consists of a patterned YBCO film on a MgO substrate and a normal metal (copper) ground plane.
successfully been applied to the development of HTS thin film technology, with examples of passive microwave and active Josephson devices that are expected to be essential ingredients in superconductive circuitry. The advantages of the PLD approach for depositing high-quality thin films of YBCO for electronic device applications begin with the simplicity of the experimental setup. All that is required is a pulsed laser (we use a Kr-F excimer laser), a vacuum chamber, a heated substrate holder, and an HTS target. With the exception of an appropriate target, all these items are commonly found in industrial and university laboratories, and the HTS target need only be homogeneous and stoichiometric in cation concentration. The simplicity of the PLD approach (laser, target, and substrate) is reflected in the very high reproducibility of the resulting films. The minimal effort required to construct a PLD system coupled with the quality and reproducibility of the resulting thin films has permitted application of this approach at numerous laboratories and to almost all classes of HTS materials (e.g., Bi, Tl, electron charge carrying HTS, and noncuprates).7"11 While the specific values of the temperature, oxygen background pressure, targetsubstrate distance, and other relevant quantities are very system dependent, high-quality thin films of c-axis-oriented YBCO (CuO2 planes oriented parallel to the substrate surface) are routinely deposited in —100-300 mtorr of oxygen from a stoichiometric target onto a latticematched substrate held at 700-800°C and positioned ~5-10 cm away. The specific values of the oxygen pressure and the substrate temperature govern the degree of orientation of the film, i.e., a-axis versus c-axis.12 The Kr-F excimer laser (A = 248 nm, E ~ 200 mj, At ~ 30 ns) typically operates at 5-10 Hz and is focused to a fluence of 1.5 J/cm2. These laser parameters yield mean deposition rates of —0.5-10 A/s of YBCO. Once deposition is complete, the chamber is filled with oxygen and the substrate is cooled to near-room temperature. Ion channeling measurements indicate a high degree of crystalline quality ( ^ ^ 3%), while transport properties reveal Tc values of -90 K, Jc values of - 4 X 106 A/cm2, and extremely low losses at microwave frequencies (Rs ~ 50-100 /JLQ, at 10 GHz, 4.2 K)13 as well as low magnetic flux noise.14-15 Electronic Device Applications Applications of superconducting films fall broadly into two categories: passive and active devices. Passive devices tend to modify a single electrical signal or input,
Data Loading...
