Enhanced Conductivity and Microstructure in Highly Textured TiN1–x/c-Al2O3 Thin Films

Titanium nitride thin films are used as an electrode material in superconducting (SC) applications and in oxide electronics. By controlling the defect density in the TiN thin film, the electrical properties of the film can achieve low resistivities and a high critical temperature (Tc) close to bulk values. Generally, low defect densities are achieved by stoichiometric growth and a low grain boundary density. Due to the low lattice mismatch of 0.7%, the best performing TiN layers are grown epitaxially on MgO substrates. Here, we report for the first time a Tc of 4.9 K for ultrathin (23 nm), highly textured (111), and stoichiometric TiN films grown on 8.75% lattice mismatch c-cut Al₂O₃ (sapphire) substrates. We demonstrate that with the increasing nitrogen deficiency, the (111) lattice constant increases, which is accompanied by a decrease in Tc. For highly N deficient TiN thin films, no superconductivity could be observed. In addition, a dissociation of grain boundaries (GBs) by the emission of stacking faults could be observed, indicating a combination of two sources for electron scattering defects in the system: (a) volume defects created by nitrogen deficiency and (b) defects created by the presence of GBs. For all samples, the average grain boundary distance is kept constant by a miscut of the c-cut sapphire substrate, which allows us to distinguish the effect of nitrogen deficiency and grain boundary density. These properties and surface roughness govern the electrical performance of the films and influence the compatibility as an electrode material in the respective application. This study aims to provide detailed and scale-bridging insights into the structural and microstructural response to nitrogen deficiency in the c-Al₂O₃/TiN system, as it is a promising candidate for applications in state-of-the-art systems such as oxide electronic thin film stacks or SC applications

Forming-Free Grain Boundary Engineered Hafnium Oxide Resistive Random Access Memory Devices

A model device based on an epitaxial stack combination of titanium nitride (111) and monoclinic hafnia (11 (Formula presented.)) is grown onto a c-cut Al 2O 3-substrate to target the role of grain boundaries in resistive switching. The texture transfer results in 120° in-plane rotated m-HfO 2 grains, and thus, in a defined subset of allowed grain boundary orientations of high symmetry. These engineered grain boundaries thread the whole dielectric layer, thereby providing predefined breakdown paths for electroforming-free resistive random access memory devices. Combining X-ray diffraction and scanning transmission electron microscopy (STEM)–based localized automated crystal orientation mapping (ACOM), a nanoscale picture of crystal growth and grain boundary orientation is obtained. High-resolution STEM reveals low-energy grain boundaries with facing ((Formula presented.)) and ((Formula presented.) 21) surfaces. The uniform distribution of forming voltages below 2 V—within the operation regime—and the stable switching voltages indicates reduced intra- and device-to-device variation in grain boundary engineered hafnium-oxide-based random access memory devices

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The Effect of Interfacial Charge Distribution on Chemical Compatibility and Stability of the High Voltage Electrodes (LiCoPO 4 , LiNiPO 4 )/Solid Electrolyte (LiPON) Interface

Solid electrolytes hold the promise of improved safety and superior electrochemical stability in energy storage systems. Among those, electrolytes with phosphate anions are expected to be more stable at high operating voltages, thereby providing even higher energy density. The key challenge is to control the boundary conditions at the cathode/electrolyte interface, which impact drastically the functionality of the energy storage devices. Here, the evolution of the chemical composition and electronic properties of the interface forms upon consequent deposition of solid electrolyte (lithium phosphorous oxynitride [LiPON]) onto the 5 V LiCoPO4 and LiNiPO4 carbon‐free thin film cathode materials is in situ studied by comprehensive electron spectroscopy experiments combined with the energy band diagram approach. It is demonstrated that the driving forces for interfacial reactivity are the band bending direction and the double layer potential drop at the electrode–electrolyte interface coupled to an unfavorable electrochemical potential shift of involved electronic states upon contact formation. The probability for interfacial chemical reactions is essentially increased at small energy differences in the ionization potentials of the cathode material and electrolyte, whereas a large energy difference ensures their chemical compatibility

Correlation of Structural Modifications by Multiscale Phase Mapping in Filamentary Type HfO2-based RRAM: Towards a Component Specific in situ TEM Investigation

Hafina based resistive random access memory (RRAM), also known as memristors, are promising candidates as next generation non-volatile memory due to their potential for high-density, high-speed, low power consumption and proven compatibility to complementary metal-oxide-semiconductor (CMOS) technology [1]. According to the current understanding, the resistive switching behavior relies on the electric field driven formation and dissolution of oxygen deficient nanoscale conducting paths often discussed as "filaments" [2]. The effects behind the mechanism include the motion of oxygen ions or creation of defects, Joule heating induced by strongly localized currents and interfacial oxygen exchange processes. All these processes are strongly related to the intrinsic material properties which are defined by the local atomic structure. By using Electron Backscatter Diffraction (EBSD, Fig.1 a-c), XRD pole figure measurements, HR- STEM imaging and automated crystal orientation mapping (ACOM) we were able to analyze the nanoscale grain structure of the multilayer and the arrangement of the monoclinic HfO2 grains in the metal-insulator-metal (MIM) stack. In the present system, the TiN/HfO2/Pt stack is deposited on a c-cut Al2O3 substrate. In an approach to change the macroscopic device properties and achieve a forming free RRAM device, the texture of the HfO2 thin film was controlled by a reactive molecular beam epitaxy synthesis routine. It allows the transfer of the substrate texture to the TiN electrode thin film and finally to the dielectric layer. Macroscopic datasets show the texture transfer (see XRD pole figures in Fig.1 f-g), where the TiN grains grow with their (111) axis parallel to the surface normal (001) of the c-cut Al2O3 and the HfO2 layer exhibit (11-1) as their out-of-plane axis. Complementary to the pole figures generated by XRD, the acquisition of high-resolution orientation mappings (Fig.1 e) allow a detailed analysis of the set of existing in-plane rotations for the m-HfO2 phase. For a single, micrometer sized grain of the TiN bottom electrode a set of three HfO2 grains is observed (Fig.1 h-i). Indicated by the crystal orientation map, the size of the HfO2 grains is proportional to the film thickness of 10 nm, resulting in grain boundaries that interconnect the top to the bottom electrode as shown in Fig.2 b. The importance of the grain boundaries mainly arises due to the existence of electronic inter-bandgap states at grain boundaries [4] and the reduced defect formation energies at these sites [3]. These physical properties strongly suggest the initial dielectric breakdown and consequent conducting path formation occurs at the grain boundary. In our electric field dependent in situ TEM studies [5], we demonstrated for the first time how to electrically contact and operate a lamella fabricated in a focused ion beam (FIB). The electrical switching characteristics of the electron-transparent lamella were comparable to a conventional reference device (Fig.2 c) [6]. 1842doi:10.1017/S1431927619009942Microsc. Microanal. 25 (Suppl 2), 2019© Microscopy Society of America 2019https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1431927619009942Downloaded from https://www.cambridge.org/core. Universitäts und Landesbibliothek Darmstadt, on 02 Dec 2019 at 12:5

Enhanced Conductivity and Microstructure in Highly Textured TiN1−x/c‑Al2O3 Thin Films

[Image: see text] Titanium nitride thin films are used as an electrode material in superconducting (SC) applications and in oxide electronics. By controlling the defect density in the TiN thin film, the electrical properties of the film can achieve low resistivities and a high critical temperature (T(c)) close to bulk values. Generally, low defect densities are achieved by stoichiometric growth and a low grain boundary density. Due to the low lattice mismatch of 0.7%, the best performing TiN layers are grown epitaxially on MgO substrates. Here, we report for the first time a T(c) of 4.9 K for ultrathin (23 nm), highly textured (111), and stoichiometric TiN films grown on 8.75% lattice mismatch c-cut Al(2)O(3) (sapphire) substrates. We demonstrate that with the increasing nitrogen deficiency, the (111) lattice constant increases, which is accompanied by a decrease in T(c). For highly N deficient TiN thin films, no superconductivity could be observed. In addition, a dissociation of grain boundaries (GBs) by the emission of stacking faults could be observed, indicating a combination of two sources for electron scattering defects in the system: (a) volume defects created by nitrogen deficiency and (b) defects created by the presence of GBs. For all samples, the average grain boundary distance is kept constant by a miscut of the c-cut sapphire substrate, which allows us to distinguish the effect of nitrogen deficiency and grain boundary density. These properties and surface roughness govern the electrical performance of the films and influence the compatibility as an electrode material in the respective application. This study aims to provide detailed and scale-bridging insights into the structural and microstructural response to nitrogen deficiency in the c-Al(2)O(3)/TiN system, as it is a promising candidate for applications in state-of-the-art systems such as oxide electronic thin film stacks or SC applications

Enhanced thermal stability of yttrium oxide-based RRAM devices with inhomogeneous Schottky-barrier

This work addresses the thermal stability of bipolar resistive switching in yttrium oxide-based resistive random access memory revealed through the temperature dependence of the DC switching behavior. The operation voltages, current levels, and charge transport mechanisms are investigated at 25 °C, 85 °C, and 125 °C, and show overall good temperature immunity. The set and reset voltages, as well as the device resistance in both the high and low resistive states, are found to scale inversely with increasing temperatures. The Schottky-barrier height was observed to increase from approximately 1.02 eV at 25 °C to approximately 1.35 eV at 125 °C, an uncommon behavior explained by interface phenomena