Fig. 2: Junction’s structure and electrical switching.
From: Bimodal ionic photomemristor based on a high-temperature oxide superconductor/semiconductor junction
a Scheme of the photo-memristor composed of a c-axis \({{{{{\rm{Y}}}}}}{{{{{{\rm{Ba}}}}}}}_{2}{{{{{{\rm{Cu}}}}}}}_{3}{{{{{{\rm{O}}}}}}}_{7-{{{{{\rm{\delta }}}}}}}\)/ITO tunnel junction grown on \({{{{{{\rm{SrTiO}}}}}}}_{3}\)(001). The micrometric junction is defined by depositing ITO into an opening through the insulating photoresist. Sketches of the YBCO/ITO interface in the OFF and ON states are displayed below. Solid and hollow circles respectively represent oxygen atoms and vacancies. b Atomic resolution Z-contrast STEM image of a YBCO/ITO bilayer grown on STO. c Cu L3 peak position along the 30 nm YBCO thin film shows a chemical shift towards higher energies at the ITO interface. d Electron energy loss spectra at the O K edge along the YBCO thin film. Gaussian fits of the oxygen pre-peak are also shown. The EELS intensity is normalized and shifted vertically to show the peak variation along the line scan. The different spectra are obtained from a line scan and correspond to 6 nm averages of the O K edge centred at (from top to bottom) 3, 9, 15, 21 and 27 nm from the interface. e Differential conductance \(G\equiv {dI}{{{{{\boldsymbol{/}}}}}}d{V}_{{read}}\) as a function of \({V}_{{read}}\) after applying a voltage pulse \({V}_{{write}}( \sim {{{{{\rm{V}}}}}})\) at T = 3.2 K to access the ON \((V_{write}\, > \,0)\) and OFF \((V_{write}\, < \,0)\) states. The inset displays the temperature dependence of the differential conductance at zero-bias \(G_{0}\)(squares) and \(V_{read}\,=\,100 \,{{{{{\rm{mV}}}}}}\) at \(G_{100}\) (circles) in the ON (solid) and OFF (hollow) states. At zero bias (\(G_0,\) squares) the conductance drops at a higher pace below a certain temperature which is close to the superconducting transition. f Hysteretic behaviour of the differential conductance as a function of the writing voltage \(V_{write}\) for \(V_{read}\,=\,100 \,{{{{{\rm{mV}}}}}}\) (\({G}_{100},\) grey, left scale) and for \(V_{read}\,=\,0\) (\(G_0,\) black, right scale), showing the maximum electrical switching amplitude \(\triangle {G}_{E}\). The junction was cycled twice from positive to negative voltages as shown by the spinning arrow. g Relaxation of the normalized conductance switching \(\Delta G_{E} (t)/G_{on}(t\,=\,0)\) as a function of time after the junction is set in the ON state (\(V_{write}\,=\,6\,{{{{{\rm{V}}}}}}\, {{{{{\rm{at}}}}}}\, {{{{{\rm{T}}}}}}\,=\,3.2\,\,{{{{{\rm{K}}}}}}\)) measured at different temperatures (see legend), along with the best fits to a stretched exponential as discussed in Supplementary Fig. S4.
