Micro-patterning of superconductive micron-sized geometric constrictions on YBCO thin films using the femtosecond laser

Abstract

In this paper a femtosecond laser is used to fabricate micron-sized superconductive constrictions. The femtosecond laser has a wavelength of 775 nm and a pulse duration of \(\:130\:\times\:\:{10}^{-15}s\) (130 fs). The power output of the laser used ranges between (0 to 1000) mW and the pulse repetition rate of the laser ranges between (1-2) kHz. This gives the laser a pulse energy of approximately 1 mJ when used. The femtosecond laser used is an Nd: YAG diode laser. The details of the main components of the femtosecond laser are given and the mode of operation of the femtosecond laser is described. The optical equipment used in the laser reflective path or the guided path to reduce the laser ablation spot size to a minimum is described. The method used to focus the laser ablation beam spot to the minimum size is described. The Atomic Force Microscope (AFM) images of the novel geometric constrictions fabricated on the YBCO thin film using the femtosecond laser are shown. The width of the two fabricated micron sized constrictions are 1.98 and 2.59 μm respectively. The laser ablation spot size used for the fabrication of the two-micron sized constrictions are 17 and 10.47 μm respectively. The I-V characterization is given for these superconductive constrictions. The critical current is \(\:{I}_{C}=1.94\:mA\) for the narrow micron junction and the critical current is \(\:{I}_{C}=4.95\:mA\) for the wider micron junction. The critical current density ( \(\:{J}_{C}\) ) is in the order of ( \(\:{10}^{4}\:A/{cm}^{2}\) ) for the two fabricated constrictions. This critical current density is slightly smaller for a similar weak link due to the thermal heating from the femtosecond laser. The superconductive constrictions can be inserted in a printed circuit board (PCB) holder and double wire bonded and the method for doing so is shown.