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The integration of complex oxides with a wide spectrum of functionalities on Si, Ge and flexible substrates is highly demanded for functional devices in information technology. We demonstrate the remote epitaxy of BaTiO3 (BTO) on Ge using a graphene intermediate layer, which forms a prototype of highly heterogeneous epitaxial systems. The Ge surface orientation dictates the outcome of remote epitaxy. Single crystalline epitaxial BTO3-δ films were grown on graphene/Ge (011), whereas graphene/Ge (001) led to textured films. The graphene plays an important role in surface passivation. The remote epitaxial deposition of BTO3-δ follows the Volmer-Weber growth mode, with the strain being partially relaxed at the very beginning of the growth. Such BTO3-δ films can be easily exfoliated and transferred to arbitrary substrates like Si and flexible polyimide. The transferred BTO3-δ films possess enhanced flexoelectric properties with a gauge factor of as high as 1127. These results not only expand the understanding of heteroepitaxy, but also open a pathway for the applications of devices based on complex oxides.

In order to fulfill the complex cognitive behaviors in neuromorphic systems with reduced peripheral circuits, the reliable electronic synapses mimicked by single device that achieves diverse long‐term and short‐term plasticity are essential. Phase change random access memory (PCRAM) is of great potential for artificial synapses, which faces, however, difficulty to realize short‐term plasticity due to the long‐lasting resistance drift. This work reports the ruthenium‐doped Ge2Sb2Te5 (RuGST) based PCRAM, demonstrating a series of synaptic behaviors of short‐term potentiation, pair‐pulse facilitation, long‐term depression, and short‐term plasticity in the same single device. The optimized RuGST electronic synapse with the high transformation temperature of hexagonal phase >380°C, the outstanding endurance >108 cycles, the low resistance drift factor of 0.092, as well as the extremely high linearity with correlation coefficients of 0.999 and 0.976 in parts of potentiation and depression. Further investigations also go insight to mechanisms of Ru doping according to thorough microstructure characterization, revealing that Ru dopant is able to enter GST lattices thus changing and stabilizing atomic arrangement of GST. This leads to the short‐term plasticity realized by RuGST PCRAM. Eventually, the proposed RuGST electronic synapses performs a high accuracy of ~94.1% in a task of image recognition of CIFAR‐100 database using ResNet 101. This work promotes the development of PCRAM platforms for large‐scale neuromorphic systems. [ABSTRACT FROM AUTHOR]

In this study, in situ synchrotron x-ray diffraction was used to investigate a high-temperature phase transition in tensile-strained epitaxial NaNbO3/(110)DyScO3 films. A ferro-to-ferroelectric phase transition was found in the temperature range between 230 and 350 °C, with a very pronounced thermal hysteresis. While at room temperature the well known monoclinic a1a2 in-plane ferroelectric phase is present, here, a slightly disturbed orthorhombic ferroelectric a1/a2 phase with exclusive in-plane polarization was found at high temperatures. This phase appeared in four variants, indicating the occurrence of four types of superdomains. The orthorhombic symmetry and the corresponding domain morphology observed at high temperatures showed a striking similarity to K0.9Na0.1NbO3 thin films grown on a (110) NdScO3 substrate. [ABSTRACT FROM AUTHOR]

The three-dimensional arrangement and orientation of domain walls in ferroelectric K0.9Na0.1NbO3/(110)NdScO3 epitaxial thin films were investigated at different temperatures both experimentally by means of piezoresponse force microscopy and three-dimensional x-ray diffraction and theoretically by three-dimensional phase-field simulations. At room temperature, a well-ordered herringbone-like domain pattern appears in which there is a periodic arrangement of a1a2/MC monoclinic phases. Four different types of domain walls are observed, which can be characterized by out-of-plane tilt angles of ±45° and in-plane twist angles of ±21°. For the orthorhombic high-temperature phase, a periodic a1/a2 stripe domain pattern with exclusive in-plane polarization is formed. Here, two different types of domain walls are observed, both of them having a fixed out-of-plane domain wall angle of 90° but distinguished by different in-plane twist angles of ±45°. The experimental results are fully consistent with three-dimensional phase-field simulations using anisotropic misfit strains. The qualitative agreement between the experiment and the theory applies, in particular, to the wide phase transition range between about 180 °C and 260 °C. In this temperature range, a complex interplay of coexisting monoclinic a1a2/MC and orthorhombic a1/a2 phases takes place. [ABSTRACT FROM AUTHOR]

Long‐term plasticity of bio‐synapses modulates the stable synaptic transmission that is quite related to the encoding of information and its emulation using electronic hardware is one of important targets for neuromorphic computing. Ge2Sb2Te5 (GST) based phase change random access memory (PCRAM) has become a strong candidate for complementary‐metal‐oxide‐semiconductor (CMOS) compatible integrated long‐term electronic synapses to cope with the high‐efficient and low power consumption data processing tasks for neuromorphic computing. However, the performance of PCRAM electronic synapses is still quite limited due to the challenges in linear and continuous conductance regulation, which originates from the fast and uncontrollable resistance switching characteristic of conventional PCRAM for the data storage application. Here an in‐depth study is reported on the impact of gallium (Ga) doping on GST (GaGST) structural properties and on the corresponding 0.13 µm CMOS technology fabricated PCRAM integrated devices with a mushroom structure. The Ga doping effectively retarded the crystallization process of GST by augmenting the local disorder of GeTe4‐nGen tetrahedron, which subsequently leads to the Set/Reset bilaterally controllable resistance switching of corresponding PCRAM devices. The optimized 6.5%GaGST electronic synapses demonstrate gradual resistance switching characteristics and a good multilevel retention feature and eventually exhibit outstanding long‐term synaptic plasticity like potentiation/depression and spiking time dependent plasticity in four forms. Such long‐term electronic synapses are applied to handwritten digits recognition (96.22%) and CIFAR‐10 image categorization (93.6%) and attain very high accuracy for both tasks. These results provide an effective method to achieve high performance PCRAM electronic synapses and highlight the great potential of GaGST PCRAM as a component for future high‐performance neuromorphic computing. [ABSTRACT FROM AUTHOR]

The properties of the conductance at the LaInO3/BaSnO3 heterointerface are reported. The heterointerface is formed by covering the semi‐insulating BaSnO3:La thin films with 10 nm LaInO3 films, which are all epitaxially grown on NdScO3 substrates. Structural properties of BaSnO3 thin films are investigated by means of X‐ray diffraction and transmission electron microscopy and exhibit a threading dislocation density of 6 × 1010 cm−2. Via capacitance–voltage (C–V) measurements, clear evidence is present for the accumulation of electrons at the interface within 2.5 nm in the BaSnO3 layer, confirming the formation of a 2D electron gas (2DEG). Additionally, temperature dependent Hall effect measurements reveal a semiconducting behavior of the electron density of the 2DEGs. The room temperature mobility of 22 cm2 V−1 s−1 at an electron density of 4 × 1013 cm−2 is found to increase as the temperature decreases to 25 K. [ABSTRACT FROM AUTHOR]