High-Tc superconductors on buffered silicon: materials properties and device applications

Abstract

Abstract The discovery of ceramic superconductors with critical temperatures that overlap the operating temperatures of most silicon devices has led to efforts to incorporate these materials into current silicon technology. Recent progress in the growth of the cuprate thin film superconductor YBa 2 Cu 3 O 7 − δ (YBCO) on buffered silicon has resulted in the development of new electronic devices. The advances in superconductor microelectronics have been remarkable compared with most other materials technologies. This paper begins with a review of the processing of the silicon substrate surface using hydrogen termination technology. Several film deposition techniques are described, namely pulsed laser deposition, metal-organic chemical vapor deposition and multi-target sputtering. The in situ growth of YBCO and buffer film on silicon substrates is also reviewed. The structural and superconducting properties of YBCO thin films are summarized. The p-type nature of YBCO gives rise to an internal electric field which can provide a basis for applications in a new class of field effect transistors. A buffer layer is necessary to prevent barium and copper in the stoichiometric YBCO compound from diffusing into the silicon substrate. The structures and electrical properties of different oxide and conducting buffers, such as yttria-stabilized zirconia (YSZ), MgO, SrTiO 3 , CeO 2 , CoSi 2 and RuO 2 , are presented. The use of these buffer layers between YBCO and Si not only serves to stabilize the YBCO/Si structure, but also provides electrical insulation or conduction in this multilayer system. The stability of this layered structure is determined to a large extent by the properties of the buffer layer and its interfaces with YBCO and Si. A detailed description of the buffer/Si and buffer/YBCO interfacial structures is given. Interfaces in a YBCO-on- buffered-Si system have been shown to impact critically on its electrical properties. The superconductor-insulator-semiconductor (SuIS) capacitor can serve as a building block for fabrication of three-or four-terminal devices such as SuIS field effect transistors (SuISFETs). The applications of superconducting thin films on buffered silicon range from single-layer superconducting interconnects to those based on fabrications of complex multilayer circuits. This paper gives a detailed description of the synthesis, processing and device physics of the SuIS capacitor or diode. Comparisons with other superconducting thin film devices, such as Josephson junctions and microwave filters and resonators, are also made. Finally, results from the fabrication and characterization of SuISFETs are presented.