Multiple Physical Time Scales and Dead Time Rule in Few-Nanometers Sized Graphene–SiO_x-Graphene Memristors

Abstract

The resistive switching behavior in SiO-based phase change memory devices confined by few nanometer wide graphene nanogaps is investigated. Our experiments and analysis reveal that the switching dynamics is not only determined by the commonly observed bias voltage dependent set and reset times. We demonstrate that an internal time scale, the dead time, plays a fundamental role in the system's response to various driving signals. We associate the switching behavior with the formation of microscopically distinct SiO amorphous and crystalline phases between the graphene electrodes. The reset transition is attributed to an amorphization process due to a voltage driven self-heating; it can be triggered at any time by appropriate voltage levels. In contrast, the formation of the crystalline ON state is conditional and only occurs after the completion of a thermally assisted structural rearrangement of the as-quenched OFF state which takes place within the dead time after a reset operation. Our results demonstrate the technological relevance of the dead time rule which enables a zero bias access of both the low and high resistance states of a phase change memory device by unipolar voltage pulses.

Experimental evidence of disorder enhanced electron-phonon scattering in graphene devices

“…18 The appearance of peaks in the conductance histogram could point to the preferential formation of specific atomic configurations, such as carbon chains, [19][20][21] or be related to transport through the SiO 2 /graphene interface. 22 Unravelling the details of tunneling transport of graphene constriction of unknown characteristics can be complicated and it is beyond the scope of this study and therefore in the following we focus on electronic and thermal transport in the diffusive transport regime. In the diffusive transport regime, the current initially increases linearly with voltage and gradually saturates at higher voltages.…”

Graphene wrinkle effects on molecular resonance states

“…The origin of these defects 6,7 and their effects on the mechanical [8][9][10] and electrical properties [11][12][13] of graphene are currently being investigated as graphenebased materials progress towards a technological stable state, reflected in the recent surge in patent applications. 14 In particular, graphene electrodes integrated in nanoscale devices serve as electrical contacts such as top-electrodes in organic solar cells, 15 bottom-electrodes in flexible electronics 16,17 and in-plane electrodes 18,19 in atomic 20 and single-molecular circuits. 21 Some commonly used techniques to obtain high-quality graphene include mechanical exfoliation, 22 epitaxial growth, 23 atomically clean graphene grown directly on single crystalline silver, 24,25 CVD growth on untreated copper foils 18,19,26 and on electropolished Cu.…”

Robust graphene-based molecular devices

“…junction variability remains high for the above-mentioned anchoring methods 13,14 , leading to poor devices reproducibility. Finally, the silicon dioxide substrate itself has been reported to yield feature-rich charge-transport characteristics 15 , in particular due to switching within the oxide 16 , which may be confused with molecular signatures. Figure 1: Junction geometry, molecular design and electrical characterization.…”

“…In addition, as the molecules are covalently bonded to the substrate, this process leads to mechanically stable graphene-molecule junctions. Moreover, the silanization process also passivates the silicon dioxide surface and prevents unwanted switching effects 16 . The second part of the molecule is the conjugated head group, specifically a bi-phenyl N-carbazole group (molecule BPC), whose orbitals can couple to the π orbitals of the graphene.…”