Proceedings Article | 2 July 1994
KEYWORDS: Superconductors, Optical lithography, Oxygen, Fabrication, Microwave radiation, Semiconductors, Optoelectronics, Optoelectronic devices, Dielectrics, Interfaces
We report our studies on the fabrication of YBa2Cu3Ox (YBCO) thin-film structures, patterned with a laser-writing technique. We demonstrate that this patterning method can be successfully implemented in fabricating a variety of electronic and optoelectronic high-Tc devices and circuits. Laser patterning implements a focused beam from a continuous-wave Ar- ion laser to selectively heat-up an epitaxial YBCO film in a controlled (oxygen or oxygen-free) atmosphere. Depending on the film's initial oxygen content and the ambient atmosphere, laser heating allows oxygen to diffuse in or out of the annealed region and form oxygen-rich (YBa2Cu3O7; superconducting) patterns next to oxygen-depleted (YBa2Cu3O6; insulating at low temperature) ones. The width of the YBa2Cu3O7- YBa2Cu3O6 interface is less than 1 micrometers . The laser-writing procedure is noninvasive, does not require a patterning mask, and results in completely planar, monolithic structures, free of surface contamination or edge degradation. Our oxygen-rich lines (typically 4 to 60 micrometers wide), patterned on the high-quality, intentionally deoxygenated YBCO films, exhibit zero resistivity at 90 K and critical current density of approximately 3 MA/cm2 at 77 K. Their superconducting properties remain unchanged even after eight months of shelf storage. On the other hand, oxygen-poor regions are semiconducting and characterized at low temperatures by a 3D, variable-length hopping transport. Below 100 K, they exhibit low microwave losses, their dc resistance is above 10 M(Omega) /square, and dielectric permittivity is below 20 at about 10 GHz. A number of devices and circuits patterned by laser writing, such as a microbridge, coplanar transmission line, open- ended coplanar microwave resonator, photoconductive switch, and YBCO field-effect transistor, are presented. All structures are intrinsic to the YBCO material, and they combine in a new and unique way superconducting and dielectric properties of the YBa2Cu3O7 and YBa2Cu3O6 phases.
