Optimizing TaOx memristor performance and consistency within the reactive sputtering “forbidden region”

Lohn, Andrew J.; Stevens, J.; Mickel, Patrick R.; Marinella, Matthew

doi:10.1063/1.4817927

Cited by 31 publications

(12 citation statements)

References 15 publications

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“…Typical parameters for switching are: Vs = -1.5 V, Ilim = 0.1 A, Is = 1 mA and Vlim = 2 V. For electroformed devices, we typically see ~5 kOhm/<500 Ohm for the HRS/LRS, respectively. No difference in electrical characteristics of electroformed devices could be correlated to size and we typically observed an 80% yield of electroformed devices indicating the good quality of the TaOx film (in agreement with previous results [22]). The resistance of these structures decreases with ion irradiation as the TaOx film becomes more conductive due to the creation of O-vacancies by the 200keV Si ++ irradiation [15,18].…”

Section: Introductionsupporting

confidence: 93%

“…Planar constructions to minimize edge effects exist [13] but filament formation and location are still governed by random and stochastic processes. Proposals to eliminate the electroforming by reducing the insulator film thickness, optimizing the stoichiometry [22,27], and creation of vacancies using broad beam irradiations [18] still rely on as grown fortuitous defects.…”

Section: Introductionmentioning

confidence: 99%

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Electroforming-free TaOx memristors using focused ion beam irradiations

et al. 2018

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We demonstrate creation of electroforming-free TaOx memristive devices using focused ion beam irradiations to locally define conductive filaments in TaOx films. Electrical characterization shows that these irradiations directly create fully functional memristors without the need for electroforming. Ion beam forming of conductive filaments combined with state-of-the-art nano-patterning presents a CMOS compatible approach to wafer level fabrication of fully formed and operational memristors.Scaling of existing Silicon based memory technologies to ultra-dense applications presents a challenge [1]. The potential for high-density nano-scale electronic switching using memristors [2][3][4] can provide a solution to scalability issues or supplement existing nonvolatile random access memory applications [5,6]. Memristors typically consist of a metal/insulator/metal stack that develops a hysteretic current-voltage loop [7,8] after electroformation of conductive filaments by applying high voltage across insulating films. A representative listing of memristors is shown in [9]. In TaOx devices, the resistance state and switching is attributed to the concentration and motion of Oxygen vacancies in or around conductive filaments, governed by applied fields and temperature gradients [9][10][11]. The relatively simple construction of memristors can be straightforwardly scaled providing a path to high-density memory and potentially for high speed, low power operation, making them attractive for future memory applications. TaOx memristors have demonstrated endurance on par with state-of-the-art flash memory [12][13][14]. In addition, previous work has shown that TaOx memristors are radiation hard to ionizing radiation [15,16], and displacement damage [17,18]. The changes in the measured filament resistance induced by ion irradiations has been primarily attributed to the creation of Oxygen vacancies in the insulating film [17,19]. However, the electro-formation process responsible for the conductive filament formation is not well controlled, remains an open topic of discussion [19,20], and the large voltages/currents required [21] cannot be easily supplied within existing CMOS architectures. The stochastic nature of this electroforming step affects device reliability and device-to-device uniformity.In this paper, we demonstrate a method to create electroforming-free TaOx memristors using focused ion beam irradiations. We use a direct write lithography platform to deterministically form a conductive filament in TaOx memristive devices at a targeted location. We show that this process creates fully operational memristors.Our method uses ion irradiations to locally modify the stoichiometry of the TaOx film deterministically creating conductive filaments at specified locations. The irradiations were performed at the Ion Beam Laboratory (IBL) at Sandia National Laboratories (SNL) using the nanoImplanter (nI) which is a 100 kV focused ion beam (FIB) system (A&D

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Section: Introductionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Electroforming-free TaOx memristors using focused ion beam irradiations

et al. 2018

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“…Even more intriguing is that these sharp IV end‐points exist at all points throughout resistive switching. Figure a shows hysteresis curves measured on TaO x memristors where the resistive switching was current‐limited for ON switching and voltage‐limited for OFF switching (fabrication details have been previously reported). The different IV end‐points apply significantly different Joule heat doses, however, each switching curve exhibits equally sharp transitions, strongly implying that

T \approx T_{c r i t}

at each switching point, and that the resistive switching is an isothermal process.…”

Section: Acknowledgementsmentioning

confidence: 99%

Isothermal Switching and Detailed Filament Evolution in Memristive Systems

et al. 2014

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The steady-state solution of filamentary memristive switching may be derived directly from the heat equation, modelling vertical and radial heat flow. This solution is shown to provide a continuous and accurate description of the evolution of the filament radius, composition, heat flow, and temperature during switching, and is shown to apply to a large range of switching materials and experimental time-scales.

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“…Therefore, as expected, exposing the device to excessive voltage or power doses will accelerate these inevitable statistical consequences. Figure 1 shows a typical bipolar current-voltage hysteresis loop, composed of four distinct regimes, measured on TaO x devices using an Agilent 4156C parameter analyzer (sample preparation has been previously described [14][15][16] ). The device begins in the OFF state (regime 1) and remains there until sufficient positive voltage (or power) is applied to the device to thermally activate the motion of ionic dopants, 10 activating ON switching (regime 2).…”

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confidence: 99%

Detection and characterization of multi-filament evolution during resistive switching

Mickel

Lohn

Marinella

2014

Applied Physics Letters

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We report resistive switching data in TaOx memristors displaying signatures of multi-filament switching modes and present a technique which enables the characterization of the evolution of multiple filaments within a single device during switching, including their temperature, heat flow, conductivity, and time evolving areas. Using a geometrically defined equivalent circuit, we resolve the individual current/voltage values of each filament and demonstrate that the switching curves of each filament collapse onto a common curve determined by the analytical steady-state resistive switching solution for filamentary switching. Finally, we discuss operational modes which may limit the formation of additional conducting filaments, potentially leading to increased device endurance.

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Optimizing TaOx memristor performance and consistency within the reactive sputtering “forbidden region”

Cited by 31 publications

References 15 publications

Electroforming-free TaOx memristors using focused ion beam irradiations

Electroforming-free TaOx memristors using focused ion beam irradiations

Isothermal Switching and Detailed Filament Evolution in Memristive Systems

Detection and characterization of multi-filament evolution during resistive switching

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