Metal-insulator Transition Material Research Articles

Thermal-electronic Integrated Circuits Using Thermally Sensitive VO2 MIT Material

Traditional integrated electronics is based only on electric signal processing, thermal phenomena are considered as a parasitic (side) effect. However, the thermal state of a device may represent information too. Thermal-electronic devices and integrated circuits can be created using power dissipating and thermally sensitive elements, such as pn junctions, thermoelectric semiconductor devices, metal-insulator transition (MIT) or semiconductor-metal transition (SMT) resistors. We propose a new active thermal-electronic device, specifically, a phonsistor = phonon transistor, patent pending [1]. The basis of the way this device operates is the thermal or hot electron coupling between adjacent domains containing metal-insulator transition (MIT) material.

Field Effect and Strongly Localized Carriers in the Metal-Insulator Transition Material VO(2).

The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13) cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3) cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2).

Quick Switch: Strongly Correlated Electronic Phase Transition Systems for Cutting-Edge Microwave Devices

The authors discuss an overview of strongly correlated electron systems and metal-insulator transition (MIT) oxide materials. Microwave applications of MIT materials are also introduced. This overview offers a vision for future microwave devices with adaptive capabilities.

Current-induced electrical self-oscillations across out-of-plane threshold switches based on VO2 layers integrated in crossbars geometry

Electrically activated metal-insulator transition (MIT) in vanadium dioxide (VO2) is widely studied from both fundamental and practical points of view. It can give valuable insights on the currently controversial phase transition mechanism in this material and, at the same time, allows the development of original MIT-based electronic devices. Electrically triggered insulator-metal transitions are demonstrated in novel out-of-plane, metal-oxide-metal type devices integrating a VO2 thin film, upon applying moderate threshold voltages. It is shown that the current-voltage characteristics of such devices present clear negative differential resistance effects supporting the onset of continuous, current-driven phase oscillations across the vanadium dioxide material. The frequencies of these self-sustained oscillations are ranging from 90 to 300 kHz and they may be tuned by adjusting the injected current. A phenomenological model of the device and its command circuit is developed, and allows to extract the analytical expressions of the oscillation frequencies and to simulate the electrical oscillatory phenomena developed across the VO2 material. Such out-of-plane devices may further contribute to the general understanding of the driving mechanism in metal-insulator transition materials and devices, a prerequisite to promising applications in high speed/high frequency networks of oscillatory or resistive memories circuits.

The VO2 interface, the metal-insulator transition tunnel junction, and the metal-insulator transition switch On-Off resistance

Transition metal compounds showing a metal-insulator transition (MIT) show complex behavior due to strongly correlated electron effects and offer attractive properties for nano-electronics applications, which cannot be obtained with regular semiconductors. MIT based nano-electronics, however, remains unproven, and MIT devices are poorly understood. We point out and single out one of the major hurdles preventing MIT-electronics: obtaining a high Off resistance and high On-Off resistance ratio in an MIT switch. We show a path toward an MIT switch fulfilling strict Off and On resistance criteria by: (1) Obtaining understanding of the VO2-interface, a protoypical MIT material interface. (2) Introducing a MIT tunnel junction concept to tune switch resistances. In this junction, the metal or insulating phase of the MIT material controls how much current flows through. Adapting the junction's parameters allows tuning the MIT switch's Off and On resistance. (3) Providing proof of principle of the junction and its switch resistance tuning capability, experimentally in two forms. (4) Showing theoretically how stringent Off and On resistance specifications can be fulfilled. The prototypical VO2 MIT results in an abrupt change in bulk electrical resistivity at ∼68 °C. We show that the VO2 MIT manifests itself in an abrupt interfacial transition of current across a VO2-barrier interface forming a tunnel junction. In a first tunnel junction form, a two orders of magnitude abrupt change in contact resistivity induced by the bulk MIT is shown in VO2-metal contact structures. VO2-metal contact properties are discussed in detail, and the work function of VO2 is found to be 5.2eV(25 °C)−5.3eV(90 °C). In a second junction form, an abrupt change in tunneling current of up to an order of magnitude caused by the bulk MIT is shown to be present in VO2-insulator-metal capacitor structures with atomic layers deposition (ALD) Al2O3 and HfO2 barrier layers. The capacitors show the feasibility of using the MIT to switch a component to a high Off resistance state. Current and capacitance-voltage characteristics of the capacitors are analyzed as well as voltage or field dependent MITs at VO2 interfaces. The abrupt change in current across the VO2 interface is shown to be driven by the change in free carriers in bulk VO2 across the MIT.

VO2, a Metal-Insulator Transition Material for Nanoelectronic Applications

An overview is given of exploratory Metal-Insulator Transition material based nanoelectronics research at imec and UGent. The VO2 thin film growth techniques used are elaborated. This considers thermal oxidation of vanadium metal and Atomic Layer Deposition (ALD). Fundamental device properties such as voltage driven switching and tunnel junction properties are discussed. Device concepts making use of MIT materials or VO2 are elaborated.

Plasmonic behaviors of gold dimers perturbed by a single nanoparticle in the gap

Modulation of resonance modes of plasmonic nanostructures at a single nanostructure level is of great importance for the development of integrated photonic chips. Recent progress of the fabrication techniques including double electron beam lithography, direct laser printing, and electron beam induced deposition has allowed the local fabrication of sub-50 nm size nanoparticles (NPs) of various materials, which provides a potential experimental realization of local impact on plasmonic behaviors of single nanostructures. In this article, we theoretically investigate that the presence of a single NP in the midgap may give rise to the excitation of new resonance modes and/or large spectral shifts of resonance modes for different plasmonic dimers (gold bowtie, nanodisk and nanorod dimers), therefore resulting in the modification of the far-field and near-field optical properties. The modification can be controlled by changing the deposition position, particle size, and material composition of the single NP. Moreover, our calculations imply that the plasmonic dimers perturbed locally by a single NP of the metal-insulator phase transition material (vanadium dioxide) in the gap can potentially act as very effective optical switch components in future photonic chips.

Microstructural evolution and electrical properties of La0.7Ca0.3MnO3 thin films grown on SrTiO3 substrates by excimer-laser assisted metal-organic deposition

Thin films of La0.7Ca0.3MnO3 were successfully grown epitaxially on (100) single-crystal SrTiO3 substrates by excimer-laser assisted metal-organic deposition. Initial amorphous LCMO thin films were obtained by metal-organic deposition at 500 °C. Crystallization and epitaxial growth of the films was achieved using a KrF pulsed laser irradiation while the film/substrate samples were kept at 500 °C. High resolution transmission electron microscopy observations on cross-sections demonstrate the formation mechanism of the epitaxial films. The crystallization process starts at the LCMO/STO interface and grows by increasing the number of laser shots. A fully crystallized film was obtained after 5 min of irradiation. The film/substrate interface was found to be sharp and abrupt. The temperature dependence of the resistance R(T) shows various behaviors, starting from insulating to semiconducting and metal–insulator transition material during the formation of the manganite film. The oxygen content was also improved by increasing the irradiation time. Promising values of the temperature coefficient of resistance were obtained from these manganite films for prospect integration in silicon based microbolometric devices.