Electric and Mechanical Switching of Ferroelectric and Resistive States in Semiconducting BaTiO3–δ Films on Silicon

Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water‐based chemical‐solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n‐doping and nanostructuring a BaTiO₃ thin film on Si(001) is explored. It is found that the ferroelectric polarization can be reversed, and resistive switching can be measured, upon a mechanical load in epitaxial BaTiO_3?δ /La_0.7Sr_0.3MnO₃/SrTiO₃/Si columnar nanostructures. A flexoelectric effect is found, stemming from substantial strain gradients that can be created with moderate loads. Simultaneously, mechanical effects on the local conductivity can be used to modulate a nonvolatile resistive state of the BaTiO_3?δ heterostructure. As a result, three different configurations of the system become accessible on top of the usual voltage reversal of polarization and resistive states.     

Iodine Vacancy Redistribution in Organic–Inorganic Halide Perovskite Films and Resistive Switching Effects

Organic–inorganic halide perovskite (OHP) materials, for example, CH₃NH₃PbI₃ (MAPbI₃), have attracted significant interest for applications such as solar cells, photodectors, light‐emitting diodes, and lasers. Previous studies have shown that charged defects can migrate in perovskites under an electric field and/or light illumination, potentially preventing these devices from practical applications. Understanding and control of the defect generation and movement will not only lead to more stable devices but also new device concepts. Here, it is shown that the formation/annihilation of iodine vacancies (V_I's) in MAPbI₃ films, driven by electric fields and light illumination, can induce pronounced resistive switching effects. Due to a low diffusion energy barrier (≈0.17 eV), the V_I's can readily drift under an electric field, and spontaneously diffuse with a concentration gradient. It is shown that the V_I diffusion process can be suppressed by controlling the affinity of the contact electrode material to I^? ions, or by light illumination. An electrical‐write and optical‐erase memory element is further demonstrated by coupling ion migration with electric fields and light illumination. These results provide guidance toward improved stability and performance of perovskite‐based optoelectronic systems, and can lead to the development of solid‐state devices that couple ionics, electronics, and optics.     

Nanoscale Correlations between Metal–Insulator Transition and Resistive Switching Effect in Metallic Perovskite Oxides

Strongly correlated perovskite oxides are a class of materials with fascinating intrinsic physical functionalities due to the interplay of charge, spin, orbital ordering, and lattice degrees of freedom. Among the exotic phenomena arising from such an interplay, metal–insulator transitions (MITs) are fundamentally still not fully understood and are of large interest for novel nanoelectronics applications, such as resistive switching‐based memories and neuromorphic computing devices. In particular, rare‐earth nickelates and lanthanum strontium manganites are archetypical examples of bandwidth‐controlled and band‐filling‐controlled MIT, respectively, which are used in this work as a playground to correlate the switching characteristics of the oxides and their MIT properties by means of local probe techniques in a systematic manner. These findings suggest that an electric‐field‐induced MIT can be triggered in these strongly correlated systems upon generation of oxygen vacancies and establish that lower operational voltages and larger resistance ratios are obtained in those films where the MIT lies closer to room temperature. This work demonstrates the potential of using MITs in the next generation of nanoelectronics devices.     

Bi2O3薄膜的制备及其电阻开关特性的研究

电阻式存储器由于具有众多的优点有望成为最有前景的下一代高速非挥发性存储器的选择之一.实验利用射频磁控溅射法在重掺硅上沉积了Bi2O3薄膜,并对该薄膜的结晶状态和Au/Bi2O3/n+Si/Al结构的电阻开关特性进行了研究.XRD分析结果表明,射频磁控溅射法沉积所得的Bi2O3薄膜结晶性能好,(201)取向明显.I-V曲线测试结果表明,Au/Bi2O3/n+Si/Al结构具有单极性电阻开关特性.通过对不同厚度Bi2O3薄膜的Au/Bi2O3/n+Si/Al结构I-V特性比较发现,随着薄膜厚度的增加,电阻开关的Forming、Set和Reset阈值电压均随之增加.对于Bi2O3薄膜厚度为31.2 nm的Au/Bi2O3/n+Si/Al结构,其Forming、Set和Reset阈值电压均低于4 V,符合存储器低电压工作的要求.     

Ag／La0.67Sr0.33MnO3/Pt异质结构的电阻开关特性

采用脉冲激光沉积技术在Pt／Ti／SiO2／Si（100）衬底上制备出多晶La0.67Sr0.33MnO3（LSMO）薄膜,对其电脉冲致非挥发可逆电阻开关特性进行研究．结果表明,Ag/LSMO／Pt结构具有明显的室温电脉冲诱发电阻开关特性,且在宽电压脉冲作用下表现出较低的开关电压和较快的变阻饱和速度．由此可见,总脉冲能量或电荷（电流作用）为该结构的电阻开关效应提供驱动力．对Ag／LsMO／Pt结构进行了耐久性测试,表明该结构具有良好的疲劳特性与保持特性,可应用于新型不挥发存储器、传感器及可变电阻等电子元器件的研制