Maskless X-Ray Writing of Electrical Devices on a Superconducting Oxide with Nanometer Resolution and Online Process Monitoring

Lorenzo Mino,Lorenza Operti,Elisa Borfecchia,Carlo Lamberti,Angelo Agostino,Valentina Bonino,Carmelo Prestipino,Matteo Fretto,Natascia De Leo,Marco Truccato

doi:10.1038/s41598-017-09443-3

Abstract

X-ray nanofabrication has so far been usually limited to mask methods involving photoresist impression and subsequent etching. Herein we show that an innovative maskless X-ray nanopatterning approach allows writing electrical devices with nanometer feature size. In particular we fabricated a Josephson device on a Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide micro-crystal by drawing two single lines of only 50 nm in width using a 17.4 keV synchrotron nano-beam. A precise control of the fabrication process was achieved by monitoring in situ the variations of the device electrical resistance during X-ray irradiation, thus finely tuning the irradiation time to drive the material into a non-superconducting state only in the irradiated regions, without significantly perturbing the crystal structure. Time-dependent finite element model simulations show that a possible microscopic origin of this effect can be related to the instantaneous temperature increase induced by the intense synchrotron picosecond X-ray pulses. These results prove that a conceptually new patterning method for oxide electrical devices, based on the local change of electrical properties, is actually possible with potential advantages in terms of heat dissipation, chemical contamination, miniaturization and high aspect ratio of the devices.

Highlights

In this scenario, the appearance of oxide electronics is opening new possibilities for the application of one-step maskless X-ray patterning methods
Since in Bi-2212 the electrical resistivity along the c-axis is about five orders of magnitude higher than in the ab-plane[21], in order to exploit the intrinsic Josephson effect, the current has to be forced to flow along the c-axis by patterning the crystal by photolithographic processes or by Focused Ion Beam (FIB) etching[22], introducing vacuum/oxide interfaces at some stage of the process to define the device geometry, which can be detrimental from the point of view of optoelectronics
In this contribution we report on the achievement of real nanometric feature size obtained by realizing a intrinsic Josephson junctions (IJJs) device drawing two single lines of only 50 nm in width

Summary

Introduction

The appearance of oxide electronics is opening new possibilities for the application of one-step maskless X-ray patterning methods. The observation that focused hard X-rays are able to modify the crystal oxygen content[14] paved the way to the practical realization of a direct-write hard X-ray patterning method where only oxide/oxide interfaces are present, suggesting that a high enough X-ray dose could locally induce in the material an oxygen depletion large enough to drive it in a non-superconducting state This idea has been recently demonstrated by fabricating a proof-of-concept IJJ device with this novel photoresist-free approach by means of synchrotron radiation, but, in spite of the nanometric sizes of the probe, only micrometric features have been obtained for the devices[23]. A real-time control of the fabrication process was achieved by monitoring in situ the variations in the electrical resistance of the sample occurring during the patterning procedure

Methods

Results

Conclusion