Microfabrication of NdFeAs(O,F) thin films and evaluation of the transport properties

Abstract

Submicron sized strip lines of NdFeAs(O,F) were fabricated and the transport properties were studied. By using laser lithography and dry etching, strip lines with a width as low as 0.84 µm were fabricated. The superconducting critical temperature was not seriously affected by the fabrication process, but a significant decrease of the critical current density (J c ) was observed for strip lines narrower than 2 µm when the sample was etched in Ar plasma. By employing a plasma free method on the other hand, the deterioration of J c was largely prevented, and the yield of obtaining strip lines with a J c higher than 5 MA cm −2 rose considerably.

Fabrication of microstrips of iron-based superconductor NdFeAs(O,H)

“…Similar to T c , the reduction in J c with decreasing the line width of the NdFeAs(O,H) microstrips fabricated under condition #2 was smaller than those of condition #1 and NdFeAs(O,F) microstrips [33] as shown in figure 3(b). During the Ar-RIE process, the thin films were etched while exposed to Ar plasma.…”

“…Here, T c of the microstrips (T c line ) was normalized to that of the films measured prior to microfabrication (T c film ). In addition, our previous results of NdFeAs(O,F) microstrips that were fabricated by Ar-RIE [33] are also plotted for comparison. As shown in figure 3(a), NdFeAs(O,H) microstrips fabricated under condition #1 retained a T c of about 90% or more of that before microfabrication down to the line width of 1.5 µm.…”

“…Studies toward the fabrication of SNSPDs using iron-based superconductors have also been reported [30][31][32][33]. LnFeAsO (Ln = lanthanoid) shows the highest T c (=56 K) among the iron-based superconductors when O is partially substituted by F or H. Our group has reported the fabrication of NdFeAs(O,F) microstrips by photolithography and Ar-ion dry etching [33]. In that study, even the narrowest microstrip with the line width of 0.84 µm preserved a high T c of about 85% of that before microfabrication.…”

“…To increase the operating temperature, efforts have been expended to fabricate SNSPDs based on high-T c superconductors [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], but this remains challenging. For example, SNSPDs for visible and infrared lights have been fabricated using MgB 2 [15][16][17][18], but their operating temperature was only about 10 K, which is much lower than the bulk T c of 39 K. For cuprates, several attempts to fabricate SNSPDs have been reported [19][20][21][22][23][24][25][26][27][28][29], and single photon detection at 25 K was recently demonstrated with SNSPDs fabricated out of exfoliated Bi 2 Sr 2 CaCu 2 O 8+δ flakes [29].…”

“…In addition, because of the increase in the total thickness due to the presence of the NdOF layer, a prolonged etching was necessary to microfabricate these thin films. This caused increased damage to the microstrips and resulted in a large decrease of the critical current density (J c ) [33].…”