Temperature Dependence of Electrically Switchable Phosphonic Acid-Based Self-Assembled Monolayer Junctions

Using organic compounds for memristive devices has garnered increased scientific interest over the past years. Recently, we have introduced a conductance-switching device based on a self-assembled monolayer (SAM) from a phosphonic acid derivative; the device's resistance exhibited a prominent hysteretic change caused by molecular dipole reorientation in the applied electric field. Here, we report on preliminary measurements of the temperature dependence of the device's electrical characteristics. Atomic force microscopy, water contact angle measurements, and Fourier-transform-infrared spectroscopy verified the quality of the SAMs. For electrical characterization, the monolayer was grown on microstructured electrodes (50 nm thick TiN bottom contact), while the top contact was achieved via electron-beam evaporation of Pb (20 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{nm}) / \text{Au}(100 \text{nm})$</tex> through a shadow mask. The hysteresis curves were analyzed for temperatures ranging from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 20 \mathrm{K}$</tex> up to 293 K. These first results indicate that below 50 K, the current densities show almost no temperature dependence, while they appear weakly activated above this threshold. The hysteretic memristive switching, which is well observed at room temperature, freezes below about 200 K - supporting the important role of intermolecular, steric interactions. For both temperature dependencies, phenomenological activation energies in the range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30-70 \text{meV}$</tex> are estimated.