Flexible Nonvolatile Memory Applications Research Articles

Lead-free (K,Na)NbO3 Thick Films for Flexible Non-volatile Memory Applications

We report the sol-gel fabrication and electrical characterization of flexible (K,Na)NbO3 (KNN) thick films. Muscovite mica allows the growth of high-quality polycrystalline KNN thick films with flexible functionality. Because of the trade-off between increase of grain-size and volatilization of alkaline ions, the electrical polarization is optimized at certain temperature of 720 °C. The remnant and saturation polarization of flexible KNN films were recorded to Pr = 10.3 μC/cm2 and Ps = 23.3 μC/cm2, respectively, which are quite close to those of rigid films with the same chemical compositions. The KNN thick films are bendable even up to bending radius of R = 3.1 mm, and the Pr and Ps at bending states are almost the same as compared to those at unbending state. Even in the convex and concave bending, the KNN thick films show excellent non-volatile memory characteristics. The Pr is almost thesameevenafter the108 times of switching and the 104 sec of retention.

High-Performance TiN/Al2O3/ZnO/Al2O3/TiN Flexible RRAM Device With High Bending Condition

The bipolar resistive switching (RS) characteristics of the ZnO-based TiN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /ZnO/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiN structure are investigated for flexible nonvolatile memory applications. Using a thin Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> buffer layer on both sides of the ZnO device shows uniform and eminently stable bipolar resistance switching characteristics. The device exhibits good RS with more than two orders of resistance ON-OFF ratio, retention of >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s at 120 °C, good dc endurance >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> cycles, and high ac endurance of >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> cycles with 40-ns pulsewidth without any degradation. The device shows high mechanical stability when under 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> continuous repetitive flexible bendings, indicating that high endurance with a very small bending radius of up to 3 mm. The lower Gibbs free energy of the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (-1676 kJ/mol) film compared with the ZnO (-320.4 kJ/mol) and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (-994 kJ/mol) films can improve the RS properties of the TiN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /ZnO/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiN device. The significant improvement in the TiN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /ZnO/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiN device is due to the reason that thin Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layers on both sides of ZnO would help stabilize the local oxygen migrations for the formation and rupture of the conductive filament during the continuous switching cycles, resulting in high memory switching characteristics.

Thermally Stable and Radiation Hard Ferroelectric Hf0.5Zr0.5O2 Thin Films on Muscovite Mica for Flexible Nonvolatile Memory Applications

Metal–ferroelectric–metal (MFM) capacitors on flexible substrates are promising for flexible nonvolatile memory applications, while the insufficient scalability of perovskite-based ferroelectric th...

Proton-irradiated Pb(Zr0.52Ti0.48)O3 thick films for flexible non-volatile memory applications

We investigated the ferroelectricity in proton-irradiated flexible Pb(Zr0.52Ti0.48)O3 (PZT) thick films and their non-volatile memory characteristics. The Ni-Cr metal foil substrate allowed high-quality polycrystalline PZT films with flexible functionality to be fabricated using conventional sol-gel and high-temperature annealing methods. The 10-MeV proton-irradiated PZT film exhibited an almost square polarization−electric field hysteresis curve with saturated (Ps) and remnant (Pr) polarizations of 18.9 and 17.0 μC/cm2, respectively; which are slightly lower than as-grown PZT with Ps = 28.7 μC/cm2 and Pr = 24.3 μC/cm2. The Pr did not decrease even after 1000 cycles of continuous bending and unbending at a bending radius of 2.14 mm and decreased slightly to ∼80% of its initial value after 105 s. Although the Pr decreased to ∼55% after 1010 cycles, the electric polarization remained switchable under positive and negative electric fields. These characteristics suggest that the flexible PZT films could be utilized in non-volatile memory device applications in environments with high doses of proton irradiation, such as those in aeronautics and nuclear power plants.

Low‐Temperature‐Processed SiOx One Diode–One Resistor Crossbar Array and Its Flexible Memory Application

AbstractThe one diode–one resistor (1D–1R) crossbar array is a promising architecture for high‐density memory due to its excellent scalability and effective suppression of the sneak paths arising from the unselected neighboring cells. In particular, the low‐temperature fabrication process plays an important role in the demonstration of the 1D–1R device, affording compatibility with conventional semiconductor processes, as well as flexible memory applications. In this study, a 1D–1R crossbar memory array consisting of a nanoporous SiOx film and an oxide‐based diode is achieved using physical vapor deposition methods at low temperature. The fabricated devices show reliable memory operation with high rectification and on/off resistance ratios under low power consumption. In addition, the low‐temperature process enables the fabrication of a flexible 1D–1R crossbar memory array on a plastic substrate. The observed uniform and stable memory performance of the flexible device under mechanical deformation establishes the feasibility of this platform for future high‐density flexible nonvolatile memory applications.

Resistive switching behavior in Lu2O3 thin film for advanced flexible memory applications

In this article, the resistive switching (RS) behaviors in Lu2O3 thin film for advanced flexible nonvolatile memory applications are investigated. Amorphous Lu2O3 thin films with a thickness of 20 nm were deposited at room temperature by radio-frequency magnetron sputtering on flexible polyethylene terephthalate substrate. The structural and morphological changes of the Lu2O3 thin film were characterized by x-ray diffraction, atomic force microscopy, and x-ray photoelectron spectroscopy analyses. The Ru/Lu2O3/ITO flexible memory device shows promising RS behavior with low-voltage operation and small distribution of switching parameters. The dominant switching current conduction mechanism in the Lu2O3 thin film was determined as bulk-controlled space-charge-limited-current with activation energy of traps of 0.33 eV. The oxygen vacancies assisted filament conduction model was described for RS behavior in Lu2O3 thin film. The memory reliability characteristics of switching endurance, data retention, good flexibility, and mechanical endurance show promising applications in future advanced memory.

Resistive switching characteristics of sol–gel based ZnO nanorods fabricated on flexible substrates

AbstractThe authors report the resistive switching characteristics of sol–gel based ZnO nanorods (NRs) fabricated on flexible substrates. A resistance ratio of 10, endurance of over 100 cycles, and narrower dispersion in the ON/OFF voltages and resistances compared to ZnO thin‐film devices are demonstrated. Furthermore, the resistive switching characteristics on flexible substrates are maintained under severe substrate bending because of the ductile properties of the nanorods. Devices composed of the Au/sol–gel based NRs/Au structure have the potential for low‐temperature flexible nonvolatile memory applications. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Resistive switching properties of TiO2 film for flexible non-volatile memory applications

Flexible electronics attracts much attention due to its advantages of flexibility and light weight. The resistive switching memory fabricated at low temperature with good performance is possibly used in the flexible electronics. In this work, an Al/TiO2/Al structural device is successfully fabricated on a flexible substrate at room temperature for the first time. The resistive switching properties of the flexible device are investigated. A possible resistive switching mechanism is proposed. The non-volatility of the flexible device is also demonstrated. Based on the experimental results, the proposed flexible device is possibly used in flexible non-volatile memory.

Interface‐Engineered Amorphous TiO2‐Based Resistive Memory Devices

AbstractCrossbar‐type bipolar resistive memory devices based on low‐temperature amorphous TiO2 (a‐TiO2) thin films are very promising devices for flexible nonvolatile memory applications. However, stable bipolar resistive switching from amorphous TiO2 thin films has only been achieved for Al metal electrodes that can have severe problems like electromigration and breakdown in real applications and can be a limiting factor for novel applications like transparent electronics. Here, amorphous TiO2‐based resistive random access memory devices are presented that universally work for any configuration of metal electrodes via engineering the top and bottom interface domains. Both by inserting an ultrathin metal layer in the top interface region and by incorporating a thin blocking layer in the bottom interface, more enhanced resistance switching and superior endurance performance can be realized. Using high‐resolution transmission electron microscopy, point energy dispersive spectroscopy, and energy‐filtering transmission electron microscopy, it is demonstrated that the stable bipolar resistive switching in metal/a‐TiO2/metal RRAM devices is attributed to both interface domains: the top interface domain with mobile oxygen ions and the bottom interface domain for its protection against an electrical breakdown.

Organic Field-Effect Transistor-Based Nonvolatile Memory Devices Having Controlled Metallic Nanoparticle/Polymer Composite Layers

Nonvolatile memory devices based on the pentacene film and controlled gold nanoparticle (Au np )/polymer composite layers were developed. Organic field-effect transistor-based nonvolatile memory devices having self-assembled Au np exhibited controllable and reliable current level differences (on- and off-states) according to the applied gate voltages (programming/erasing operations). The memory devices showed large memory windows as well as good data retention properties by adopting charge storage layers of controlled Au np separated by insulating polymer layers. The process for fabricating nonvolatile memory devices was based on the solution processes and organic semiconductor layers, so it has a potential use in flexible nonvolatile memory applications.