Conductance Quantization in Resistive Random Access Memory

based on a resistive switching Pt/TiO 2−x / TiO 2 /Pt device (Figure 1b), since when the long-standing resistive switching devices over the past half century were all regarded as memristors [3] and aroused ever increasing research interest all over the world for promising nonvolatile memory, logic-in-memory as well as neuromorphic computing applications. [4][5][6][7][8] Memristors usually consist of a simple "metal/insulator/metal" sandwich structure and can be reversibly switched between a high resistance state (HRS, or off state) and a low resistance state (LRS, or on state) under external electrical stimuli. [6] Despite various switching mechanisms have been proposed and solidly confirmed, [7,8] of particular interest and importance is the ion migration-based filamentary mechanism that can ensure an enhanced performance as the device scaling down (Figure 1c). Excellent device miniaturization of <10 nm, [9,10] ultrafast operation speed of <1 ns, [11,12] and extreme switching endurance of >10 12 cycles [13] have been demonstrated in memristors with filamentary mechanism, in addition to their abundant storage media including oxides, nitrides, chalcogenides, polymers, and etc. [7,8] Room-temperature quantum conductance has also been found in these memristors when the size of conducting filaments is reduced down to atomic scale, [14][15][16] as schematically shown by the panels (ii) and (iii) in Figure 1c. In this scenario, the device conductance G is able to be expressed as

Section: Experimental Phenomenamentioning

confidence: 99%

Section: Wwwadvelectronicmatdementioning

confidence: 99%

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Recent Advances of Quantum Conductance in Memristors

Xue

Gao

Shang

et al. 2019

“…[20][21][22] Exploration of the quantized conductance of APCs in memristors can date back to 2005, when Aono and coworkers first demonstrated conductance quantization in solid electrolyte-based atomic switch devices. [27][28][29] Nevertheless, the basic understanding about the essence of local ion rearrangement and APC evolution dynamics is still inadequate, from aspects of both materials design and fundamental physics. For instance, both metal cations and oxygen anions are utilized to construct APCs through their migration, local rearrangement, and electrochemistry in insulating matrix of SiO x , ZnO, ZrO x , HfO x , TiO x , TaO x , polyethylene oxide (PEO), amorphous carbon, etc.…”

Section: Introductionmentioning

confidence: 99%

Controllable and Stable Quantized Conductance States in a Pt/HfO_x/ITO Memristor

Xue

Liu

et al. 2019

computation-in-memory paradigm with new electronic devices when handling data-intensive tasks. [1,2] One important attempt is the recently well explored memristor, [3][4][5] in which the nonlinear dynamics of the device allows on demand modulation of the conductance for direct logic operation while the capability of memorizing the new conductance state enables data storage at exactly the same physical location. [6,7] Eliminating the frequent data fetching and movement between the separated memory and processing units, memristors with the simplicity of a resistor structure can lead to extremely compact crossbar array for highly efficient hardware systems. [8,9] In particular, the elaborate evolution of the conductive filament via local ion motion and electrochemistry including foreign cations (such as Ag + and Cu 2+ injected from electrochemically active metal electrodes) and native oxygen anions or vacancies (O 2− or V O ) are widely used to construct atomic point contacts (APCs) with quantized conductance features. [10][11][12][13][14] The stepwise development of device conductance in the unit of conductance quantum G 0 = 2e 2 /h = 77.5 µS (where e is the elemental charge of electrons and h is the Planck's constant), [10] associated with the continuous yet precise atomic Quantum-level manipulation of atomic configuration offers a excellent platform for the construction of exotic nanostructures that exhibit unusual solid-state physics and electronic properties. One particular example is the memristor, in which the elaborate evolution of atomic point contact via local ionic processes and consequent stepwise device conductance quantization enable bottom-up design of in-memory computing with greatly increased data storage density and more efficient multi-value logic algorithm. In-depth understanding on the physics of atomic reconfiguration is achieved through comprehensive consideration of the thermodynamics and kinetics of nanoionics in memristors, based on which a general protocol of constructing atomic point contact structure with desired quantized conductance is established. Through energy-driven single-atom level oxygen manipulation in the reset process of a Pt/HfO x /ITO structure, up to 32 consecutive quantized conductance states with an interval of half conductance quantum that can be sustained for over 7000 s and tuned 500 times are demonstrated for the first time, not only allowing the physical implementation of ternary logic-inmemory functions, but also providing a universal methodology for building next-generation quantum electronic devices.

“…[6] Electronic switches with atomicsized functional building blocks are the main driving force of modern nanotechnology. [6] Electronic switches with atomicsized functional building blocks are the main driving force of modern nanotechnology.…”

mentioning

confidence: 99%

Quantized Conduction Device with 6‐Bit Storage Based on Electrically Controllable Break Junctions

Banerjee

Hwang

2019

electron charge and h is the Planck constant. [6] Electronic switches with atomicsized functional building blocks are the main driving force of modern nanotechnology. The design of atomic dimensional memory devices is limited by the lithographic bottleneck. Nevertheless, the origin of atomic contact in nanoscale architectures is being investigated. [7] The conductive bridge RAM device with quantized conductance (QC) effect proposed by Terebe et al., [8] was based on the fabrication of a gap-type Pt/ nano-gap/Ag 2 S/Ag structure. A small operating voltage of ±600 mV can switch the device between the "OFF" and "ON" states. When a device changes its resistance from high to low, it is usually known as "set"; the reverse change is known as "reset". The QC effect is suitable to realize multiple levels in devices and has been studied in both electrochemical metallization type [9][10][11][12][13][14] and valance change memory type [15,16] gap-less RRAM. In most cases, switching is the after-effect of a stress dependent virginity breakdown, which can consolidate the CF for switching operations. Because the behavior of the CF of conductive bridge RAM is considered to be an example of atomic-switching, further discussion is mainly focused on conductive bridge RAM type devices. Higher initial stress injects more cations into the switching oxide layer that results in poor control over the reset process, resulting in abrupt state transition, and atomic conductance instability. [9][10][11][12][13][14] In another approach, single-atom memory has been proposed for mechanically controllable break junctions (MCBJs), [17] which are a kind of electronic device formed by two knife-edged metal wires placed with a nanometer sized gap, as shown in Figure 1a. MCBJs are well known as atomic or single molecular junction, and have even been investigated to in the context of control of quantum interferences in graphene. [18,19] In an MCBJ, when the two wires are curved, broadening the gap, the contact is broken, and the reverse order experiences an atomic-contact at the break junction. Break junctions are a possible approach to the fabrication of atomic switches. However, in reality, for an electronic device, such design is burdensome due to exorbitant lithographic processes. It is possible to prepare a break junction by electrically controlling the ion migration process in conductive bridge RAM devices, as the switching mechanism is driven by the formation of metallic wire like CF. Although the concept of QC in conductive bridge RAM has been investigated for over a decade, precise and reliable atomic-level control Atomic-level control of conductance in a Cu/Ti/HfO 2 /TiN-based electrically controllable break junction (ECBJ) is demonstrated. The ECBJ is designed through sophisticated stack engineering and refined electrical operation. Control over bias-induced ion migration is the key to forming the ECBJ. Precise atomic-level control is accomplished with an optimized high temperature forming (OHTF) scheme. OHTF-controlled single-atomic switch...