Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

This review article attempts to provide a comprehensive review of the recent progress in the so-called resistive random access memories (RRAMs) First, a brief introduction is presented to describe the construction and development of RRAMs, their potential for broad applications in the fields of nonvolatile memory, unconventional computing and logic devices, and the focus of research concerning RRAMs over the past decade Second, both inorganic and organic materials used in RRAMs are summarized, and their respective advantages and shortcomings are discussed Third, the important switching mechanisms are discussed in depth and are classified into ion migration, charge trapping/de-trapping, thermochemical reaction, exclusive mechanisms in inorganics, and exclusive mechanisms in organics Fourth, attention is given to the application of RRAMs for data storage, including their current performance, methods for performance enhancement, sneak-path issue and possible solutions, and demonstrations of 2-D and 3-D crossbar arrays Fifth, prospective applications of RRAMs in unconventional computing, as well as logic devices and multi-functionalization of RRAMs, are comprehensively summarized and thoroughly discussed The present review article ends with a short discussion concerning the challenges and future prospects of the RRAMs

Recent progress in resistive random access memories: Materials, switching mechanisms, and performance

The conduction mechanisms in dielectric films are crucial to the successful applications of dielectric materials. There are two types of conduction mechanisms in dielectric films, that is, electrode-limited conduction mechanism and bulk-limited conduction mechanism. The electrode-limited conduction mechanism depends on the electrical properties at the electrode-dielectric interface. Based on this type of conduction mechanism, the physical properties of the barrier height at the electrode-dielectric interface and the effective mass of the conduction carriers in dielectric films can be extracted. The bulk-limited conduction mechanism depends on the electrical properties of the dielectric itself. According to the analyses of bulk-limited conduction mechanisms, several important physical parameters in the dielectric films can be obtained, including the trap level, the trap spacing, the trap density, the carrier drift mobility, the dielectric relaxation time, and the density of states in the conduction band. In this paper, the analytical methods of conduction mechanisms in dielectric films are discussed in detail.

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A Review on Conduction Mechanisms in Dielectric Films

This paper reviews the present knowledge on tantalum pentoxide (Ta 2 O 5 ) thin films and their applications in the field of microelectronics and integrated microtechnologies. Different methods used to produce tantalum oxide layers are described, emphazing elaboration mechanisms and key parameters for each technique. We also review recent advances in the deposition of Ta 2 O 5 in the particular field of microelectronics where high quality layers are required from the structural and electrical points of view. The physical, structural, optical, chemical and electrical properties of tantalum oxide thin films on semiconductors are then presented and essential film parameters, such as optical index, film density or dielectric permittivity, are discussed. After a reminder of the basic mechanisms that control the bulk electrical conduction in insulating films, we carefully examine the origin of leakage currents in Ta 2 O 5 and present the state-of-the-art concerning the insulating behaviour of tantalum oxide layers. Finally, applications of tantalum oxide thin films are presented in the last part of this paper. We show how Ta 2 O 5 has been employed as an antireflection coating, insulating layer, gate oxide, corrosion resistant material, and sensitive layer in a wide variety of components, circuits and sensors.

Tantalum pentoxide (Ta2O5) thin films for advanced dielectric applications

Dielectric capacitors with ultrahigh power densities are fundamental energy storage components in electrical and electronic systems. However, a long-standing challenge is improving their energy densities. We report dielectrics with ultrahigh energy densities designed with polymorphic nanodomains. Guided by phase-field simulations, we conceived and synthesized lead-free BiFeO3-BaTiO3-SrTiO3 solid-solution films to realize the coexistence of rhombohedral and tetragonal nanodomains embedded in a cubic matrix. We obtained minimized hysteresis while maintaining high polarization and achieved a high energy density of 112 joules per cubic centimeter with a high energy efficiency of ~80%. This approach should be generalizable for designing high-performance dielectrics and other functional materials that benefit from nanoscale domain structure manipulation.

Ultrahigh–energy density lead-free dielectric films via polymorphic nanodomain design

Tantalum oxide (Ta2O5) is an important material for future dynamic random access memory application owing to its high dielectric constant This work examines the structural and electrical properties of Ta2O5 thin films deposited by plasma-enhanced chemical vapor deposition using a penta ethoxy tantalum Ta(OC2H5)5 liquid source The x-ray diffraction patterns indicate that the as-deposited thin films are amorphous and become polycrystalline after rapid thermal annealing above 650 °C The level of carbon contamination is below that which can be detected by Auger electron spectroscopy measurement Electrical measurements performed on amorphous Ta2O5 using a Au/Ta2O5/Pt/Ti/Si metal-tantalum oxide-metal structure exhibit a low leakage current, reasonable breakdown field (54 MV/cm), and high dielectric constant (23–25) The leakage current is 2×10−8 A/cm2 at 1 MV/cm In addition, the leakage current mechanism of amorphous Ta2O5 capacitors is investigated by plotting the ln(J) vs E1/2 curves at a low electric field ( 2 MV/cm) The dominant conduction mechanism is due to Schottky emission at low electrical field and Poole–Frenkel emission at high electrical field According to our results, the Ta2O5 thin films annealed in N2 or O2 at 800 °C exhibit a much higher leakage current than amorphous Ta2O5 , possibly due to the out-diffusion of Ti during high temperature annealing

Leakage currents in amorphous Ta2O5 thin films

Metal-oxide-semiconductor capacitors that incorporate La2O3 dielectric films were deposited by radio frequency magnetron sputtering. In this work, the essential structures and electrical properties of La2O3 thin films were investigated. Capacitance–voltage, energy dispersive x-ray spectrometry, and transmission electron microscopy analyses reveal that an interfacial layer was formed, subsequently reducing the effective dielectric constant of the 700°C annealed La2O3 thin films. The dominant conduction mechanism of the Al∕La2O3∕p-Si metal-lanthanum oxide-semiconductor capacitor is space-charge-limited current from 300to465K in the accumulation mode. Three different regions, Ohm’s law region, trap-filled-limited region, and Child’s law region, were observed in the current-density–voltage (J–V) characteristics at room temperature. The activation energy of traps calculated from the Arrhenius plots was about 0.21±0.01eV. The electronic mobility, trap density, dielectric relaxation time, and density of states i...

Electrical conduction mechanisms of metal∕La2O3∕Si structure

The optical dielectric function of cerium oxide (CeO2) was characterized by the spectroscopic ellipsometry (SE) technique using the Kramers?Kronig relation and the Tauc?Lorentz (TL) dispersion model. Experimental results showed that the bandgap energy and refractive index at 632.8?nm of CeO2 are about 3.23 ? 0.05?eV and 2.33 ? 0.08, respectively. Based on the optical properties, the electrical conduction mechanisms in CeO2 thin films are determined to be Schottky emission in a medium electric field (0.5?1.6?MV?cm?1) from 350 to 500?K and Poole?Frenkel emission in a high electric field (>2.36?MV?cm?1) from 450 to 500?K. Accordingly, the conduction band offsets between Al and CeO2 and the trap energy level are about 0.62 ? 0.01?eV and 1.53 ? 0.01?eV, respectively.

https://iopscience.iop.org/article/10.1088/0022-3727/43/7/075104/pdf

Optical and electrical characterizations of cerium oxide thin films

In this work, bipolar resistive switching characteristics were demonstrated in the Pt/ZnO/Pt structure. Reliability tests show that ac cycling endurance level above 106 can be achieved. However, significant window closure takes place after about 102 dc cycles. Data retention characteristic exhibits no observed degradation after 168 h. Read durability shows stable resistance states after 106 read times. The current transportation in ZnO films is dominated by the hopping conduction and the ohmic conduction in high-resistance and low-resistance states, respectively. Therefore, the electrical parameters of trap energy level, trap spacing, Fermi level, electron mobility, and effective density of states in conduction band in ZnO were identified.

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Fu-Chien Chiu

Papers

A Review on Conduction Mechanisms in Dielectric Films

Leakage currents in amorphous Ta2O5 thin films

Electrical conduction mechanisms of metal∕La2O3∕Si structure

Optical and electrical characterizations of cerium oxide thin films

Reliability characteristics and conduction mechanisms in resistive switching memory devices using ZnO thin films