Search

The retention behavior of a HfO2 resistive switching memory device with a diameter of 28 nm and an ultra-thin (1 nm) HfO2 layer as the switching layer was examined. Ta and TiN served as the oxygen vacancy (VO) supplying the top and inert bottom electrodes, respectively. Unlike the retention failure phenomenon reported in other thicker oxide-based resistance switching memory devices, the current of both the low and high resistance states suddenly increased at a certain time, causing retention failure. Through the retention tests of the devices in different resistance states, it was concluded that the involvement of the reset step induced the retention failure. The pristine device contained a high portion of VO-rich region and the location of the border between the VO-rich and VO-free regions played the critical role in governing the retention performance. During the reset step, this borderline moves towards the Ta electrode, but moves back to the original location during the retention period, which eventually induces the reconnection of the disconnected conducting filament (in a high resistance state) or strengthens the connected weak portion (low resistance state). The activation energy for the retention failure mechanism was 0.15 eV, which is related to the ionization of neutral VO to ionized VO. [ABSTRACT FROM AUTHOR]

Mesostructured silica films with a well-ordered Im3m structure and enhanced surface properties can be synthesized by means of cosolvent addition and the optimization of sol aging time. Mesostructured silica films fabricated using ethanol, a commercial solvent, result in wavy surface properties induced by the Marangoni effect irrespective of rotation speed during spin coating. In order to improve the surface roughness, we used an ethanol-acetone mixture as a solvent with a certain molar ratio. Wavy and rough films could be avoided when the acetone molar ratio was optimized. The simultaneous increase of unit cell size and thickness of the film was observed when the amount of cosolvent was increased. The unit cell was also enlarged with sol aging time, and well-ordered mesoporous silica films could be synthesized by controlling the silica sol aging. The dielectric property could be improved by means of cosolvent addition only after the development of a highly ordered mesoporous nature of the film by calcination. The leakage current of the mesoporous silica film could be reduced when the structural ordering and surface roughness were controlled. [ABSTRACT FROM AUTHOR]

To commercialize phase change memory (PCM), a drastic change of resistivity at specific temperatures and a low power consumption to minimize heat transfer to neighboring cells are needed. Therefore, in this work, an ordered mesoporous SiO2 thin film of 45% porosity was introduced as an intercell dielectric in Ge1Sb4Te7 PCM because it has a low thermal conductivity (0.177 W/m K). By using a hybrid layer structure of mesoporous and dense SiO2 films, the temperature of neighboring cells could be decreased from 393.3 K to 353.2 K, corresponding to a 100-fold change in resistivity. [ABSTRACT FROM AUTHOR]

Mesoporous materials have pores with diameters between 2 nm and 50 nm, the presence of which generally decreases the thermal conductivity of the material. By incorporating mesoporous structures into thermoelectric materials, the thermoelectric properties of these materials can be improved. Although TiO is an ordinary insulator, reduced TiO shows better electrical conductivity and is therefore a potential thermoelectric material. Furthermore, the addition of a dopant to TiO can improve its electrical conductivity. We hypothesized that, by doping ordered mesoporous TiO films with niobium, we would be able to minimize the thermal conductivity and maximize the electrical conductivity. To investigate the effects of Nb doping and a mesoporous structure on the thermoelectric characteristics of TiO films, Nb-doped mesoporous films were investigated using x-ray diffraction, ellipsometry, four-point probe measurements, and thermal conductivity analysis. We found that Nb doping of ordered mesoporous TiO films improved their thermoelectric properties. [ABSTRACT FROM AUTHOR]

Pseudomorphic high electron mobility transistors (PHEMTs) are promising devices for use in millimeter-wave and optical communications systems due to their excellent high frequency and low-noise performances. In order to further improve the performance of these devices, their gate lengths must be reduced to the technological limit and a small gate resistance must be realized. However, shorter gates result in an increase of short channel effects that limit microwave performance. In order to reduce the gate resistance, T-shaped gates with large cross-sectional areas are required. However, the thickness and dielectric constant of the passivation layer have major impacts on the gate capacitance. In this study, an ordered mesoporous silica film was introduced as a passivation layer between T-gates. SiN with a dielectric constant of 7.4 and ordered mesoporous silica with a dielectric constant of 2.48 were used as passivation layers. The SiN dielectric layer and the ordered mesoporous silica film were stacked together and the device characteristics were investigated. [ABSTRACT FROM AUTHOR]

Conductive bridge random access memory (CBRAM) has been regarded as a promising candidate for the next‐generation nonvolatile memory technology. Even with the great performance of CBRAM, the global generation and overinjection of cations after much repetitive switching cannot be prevented. The overinjection of cations into an electrolyte layer causes high‐resistance‐state resistance (RHRS) degradation, on/off ratio reduction, and eventual switching failure. It also degrades the switching uniformity. In this work, a Cu‐cone‐structure‐embedded TiN/TiO2/Cu cone/TiN device is fabricated to alleviate the problems of Cu‐based CBRAM, mentioned above. The fabrication method of the device, which is useful for laboratory scale experiment, is developed, and its superior switching performance and reliability compared with the conventional planar device. The insertion of the Cu cone structure allows the placement of only a limited amount of cation source in each cell, and the embedded conical structure also concentrates the applied electric field, which enables filament growth control. Furthermore, the concentrated field localizes the resistive switching on the tip area of the cone structure, which makes the effective switching area about tens of nanometers even for the much larger area of the entire electrode (several µm2). This work proposes Cu‐cone‐embedded conductive bridge random access memory (CBRAM), whose stack is TiN/TiO2/Cu cone/TiN. The applied electric field is concentrated on the tip of the conical structure, which induces single‐filament formation and enhances the switching reliability. Moreover, the effective switching area is reduced to tens of nanometers due to the locally concentrated field, and a scalability effect is achieved. [ABSTRACT FROM AUTHOR]

Ordered mesoporous TiO2 films with incorporated Pt nanoparticles were prepared using titanium tetraisopropoxide, hexachloroplatinic acid hexahydrate, and Pluronic P-123 as a titania precursor, a Pt precursor, and a structure-directing agent, respectively. Pt nanoparticles were introduced to enhance the electrical properties of the mesoporous films, which have excellent thermal insulation properties. We confirmed that the synthesized composite films with Pt nanoparticles had an ordered pore structure with anatase phase TiO2 by both small-angle and wide-angle X-ray diffraction analyses. Although the porosity of the composite film decreased from 37.6 to 29.3% when Pt nanoparticles were included, the conductivity ratio (σ/κ) of the film increased greatly, up to approximately 1370 K V-2, due to the greater increase in electrical conductivity than thermal conductivity. Based on our results, we conclude that by incorporating Pt nanoparticles into ordered mesoporous TiO2 film, the thermoelectric properties of the mesoporous films can be improved. [ABSTRACT FROM AUTHOR]