Abstract
Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 1017 m−2. We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching.
Highlights
Many metal-insulator-metal (MIM) systems show nonvolatile, electrically induced resistive switching and have been proposed as replacements for standard NAND-flash non-volatile circuitry.1 A large variety of materials can give rise to resistive switching2–4 including organic semiconductors.5–9 The operating mechanism of organic memory cells is under intense investigation
The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching
Unipolar resistive switching in Al2O3/organic semiconductor diodes involves defects in the oxide that are created during electroforming
Summary
Many metal-insulator-metal (MIM) systems show nonvolatile, electrically induced resistive switching and have been proposed as replacements for standard NAND-flash non-volatile circuitry. A large variety of materials can give rise to resistive switching including organic semiconductors. The operating mechanism of organic memory cells is under intense investigation. The switching can be induced by applying voltage pulses. When voltage pulses of the same polarity are used the switching is called unipolar. Reversible switching requiring voltage pulses of opposite polarity is referred to as bipolar. Switching in hybrid Al2O3 memories is unipolar. Electroforming and resistive switching was first reported in 1962 by Hickmott for thin anodic Al2O3 films.. In this study we focus on electroforming and resistive switching in Al2O3/polymer diodes. Statistical thermodynamics of phase transitions in 2D systems is used to explain the unipolar switching in the fabricated memories.
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