Abstract
Two-dimensional electron gases (2DEGs) can be formed at some oxide interfaces, providing a fertile ground for creating extraordinary physical properties. These properties can be exploited in various novel electronic devices such as transistors, gas sensors, and spintronic devices. Recently several works have demonstrated the application of 2DEGs for resistive random-access memories (RRAMs). We briefly review the basics of oxide 2DEGs, emphasizing scalability and maturity and describing a recent trend of progression from epitaxial oxide interfaces (such as LaAlO3/SrTiO3) to simple and highly scalable amorphous-polycrystalline systems (e.g., Al2O3/TiO2). We critically describe and compare recent RRAM devices based on these systems and highlight the possible advantages and potential of 2DEGs systems for RRAM applications. We consider the immediate challenges to revolve around scaling from one device to large arrays, where further progress with series resistance reduction and fabrication techniques needs to be made. We conclude by laying out some of the opportunities presented by 2DEGs based RRAM, including increased tunability and design flexibility, which could, in turn, provide advantages for multi-level capabilities.
Highlights
Two-dimensional electron gases (2DEGs) can be formed at some oxides interfaces [1]. These oxide interfaces provided a fertile ground for the discovery and manipulation of extraordinary physics, such as superconductivity [2,3,4,5], magnetism [6, 7], magnetoelectric coupling [8, 9], Rashba spinorbit coupling [10], persistent photoconductivity [11, 12], and integer/fractional quantum Hall effect [13, 14]
Oxide 2DEGs were first reported in epitaxial oxide interfaces, where a complex oxide such as LaAlO3 is grown, typically by pulsed laser deposition (PLD), on a single-crystal oxide substrate, typically SrTiO3 [1, 2] (Figure 1A)
We briefly review the oxide material systems hosting 2DEGs, focus on their application in the resistive random-access memories (RRAMs) devices, and discuss the challenges and opportunities for 2DEGs in RRAM applications
Summary
Two-dimensional electron gases (2DEGs) can be formed at some oxides interfaces [1]. These oxide interfaces provided a fertile ground for the discovery and manipulation of extraordinary physics, such as superconductivity [2,3,4,5], magnetism [6, 7], magnetoelectric coupling [8, 9], Rashba spinorbit coupling [10], persistent photoconductivity [11, 12], and integer/fractional quantum Hall effect [13, 14]. While potentially scalable [75], they remain slow, expensive, and high temperature (∼600°C) and fall far behind the non-epitaxial ALD approaches This chronological trend of simplifying the materials and fabrication techniques has seen the transition from epitaxial interfaces (e.g., single crystalline LaAlO3/single crystalline SrTiO3, Figure 1A) to amorphous oxides on single-crystals (e.g., a-LaAlO3/single crystalline SrTiO3, Figure 1B), and recently to All-ALD 2DEGs with amorphous-polycrystalline systems (e.g., amorphous Al2O3/polycrystalline TiO2, Figure 1C). The interface conductivity results from ionic defects formed during the high-temperature step and possibly kinetic damage from the PLD process This use of amorphous layers constitutes progress toward simplifying the materials and deposition techniques. They demonstrated a Cu conductive filament device based on 2DEG formed between amorphous Al2O3 and polycrystalline anatase TiO2 (Figure 1C) Both materials were fabricated by ALD (250°C).
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