Electric-field modulation of a Bi-Sr-Ca-Cu-O film with a polymer film as an insulator
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Electric-field modulation of a Bi-Sr-Ca-Cu-CO film with a polymer film as an insulator Shin'ichi Morohashi, Hideo Suzuki, Kohtaroh Gotoh, Norio Fujimaki, and Shinya Hasuo FUJITSU LIMITED, 10-1 Morinosato Wakamiya Atsugi, JAPAN
Abstract We fabricated the multilayered structure with Au gate electrode/polymer film/Bi-Sr-Ca-Cu-O film to study the electric-field control of high Tc superconductor. A Bi-Sr-Ca-Cu-O(BSCCD) film was fabricated using an ion beam sputtering technique. The plasma polymerization using trifluoroethane gas was used to make the gate insulator. The patterning of the BSCCO film was carried out using an ion beam etching technique. The supercurrent of the decreased when the gate voltage was applied to the gate structure electrode.
Introduction High-Tc superconducting devices are expected as future electronic devices. One of the technology to realize these devices is to utilize the electric-field control of high-Tc superconductor. The trials for testing the structure had been carried out using superconductors such as Sn and In/InOx[1-3]. A voltage applied to the gate electrode induces a charge which modifies the properties of the superconductor, and the source -to-drain resistance changes from zero for Vg =0 to the normal state resistance for Vg#0. Using very thin films, this would be feasible with high Tc superconductor because of the relatively low carrier density compared with other superconductor such as Nb[4]. In addition, we must prepare the thin insulator film without leak current, and the dry etching process with damage free. In this paper, We report these fabrication process to make the multilayered structure for testing FET structure, and the I-V characteristic of the structure.
Fabrication process The BSCCD film was deposited on MgO(100) substrate using the ion beam sputtering technique, which a cold cathode magnetron ion source was used. A single ceramic target was used. Its composition was compensated such as those of the film was to be Bi:Sr:Ca:Cu=1:1:1:2. The operation pressure was 5x10-2 Pa using the cryo pump. The Ar+50%02 gas was used as the sputtering gas, whose flow rate of 15 sccm was controlled by mass flow meter. The substrate was heated up to 840 aC through radiant heat using infrared lumps. The discharge and extraction voltages for ion source were 0.4 and 2.4 Kev, respectively. The deposition rate was about 3.0 nm/min under these conditions. The deposited film was experienced through the in-situ and post annealing process. The in-situ annealing process was carried out under the conditions indicated in Table I. The in-situ annealed film showed the Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
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Table. I In-situ annealing conditions Temperature
840 *C
Time
Gas
Pressure
3 min
02
133 Pa
mixture of the 80 and 110 K phases, identified from the X-ray diffraction pattern. The zero resistance of the film(Tc) was 85 K, though the resistivity was almost dropped near 110 K. The film was post annealed at 850 ýC for 60 min in the atmosphere of the mixt
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