Detection of the insulating gap and conductive filament growth direction in resistive memories.

Filament growth is a key aspect in the operation of bipolar resistive random access memory (RRAM) devices, yet there are conflicting reports in the literature on the direction of growth of conductive filaments in valence change RRAM devices. We report here that an insulating gap between the filament and the semiconductor electrode can be detected by the metal-insulator-semiconductor bipolar transistor structure, and thus provide information on the filament growth direction. Using this technique, we show how voltage polarity and electrode chemistry control the filament growth direction during electro-forming. The experimental results and the nature of a gap between the filament and an electrode are discussed in light of possible models of filament formation.

Reply to the 'Comment on "How to interpret Onsager cross terms in mixed ionic electronic conductors"' by H.-I. Yoo, M. Martin, and J. Janek, Phys. Chem. Chem. Phys., 2015, 7, DOI: 10.1039/C4CP05737F.

The origin of the Onsager cross terms in mixed-ionic-electronic-conductor (MIEC) oxides is re-examined. Experiments are suggested to determine which of the two suggested explanations is applicable.

Nonlinear I-V relations and hysteresis in solid state devices based on oxide mixed-ionic-electronic conductors.

The current-voltage, I-V, relations as well as the defect distributions are calculated for solid state devices in which the acceptors are mobile. The devices are of the metal|oxide|metal (MOM) type, where the oxide is a mixed-ionic-electronic conductor. The electrodes are blocking for material exchange. I-V relations are calculated for cyclic voltammetry, high amplitude ac voltage and low amplitude ac voltage from which the ac impedance is derived. The results exhibit nonlinear I-V relations, energy storage, hysteresis, negative resistance and quasi-switching.