Minjuan Wang

Implementation of Complete Boolean Logic Functions in Single Complementary Resistive Switch.

The unique complementary switching behaviour of complementary resistive switches (CRSs) makes them very attractive for logic applications. The implementation of complete Boolean logic functions in a single CRS cell is certainly an extremely important step towards the commercialisation of related logic circuits, but it has not been accomplished to date. Here, we report two methods for the implementation of complete Boolean logic functions in a single CRS cell. The first method is based on the intrinsic switchable diode of a peculiar CRS cell that is composed of two anti-serial bipolar resistive switches with a rectifying high resistance state, while the second method is based directly on the complementary switching behaviour itself of any single CRS cell. The feasibilities of both methods have been theoretically predicted and then experimentally demonstrated on the basis of a Ta/Ta2O5/Pt/Ta2O5/Ta CRS cell. Therefore, these two methods—in particular the complementary switching behaviour itself-based method, which has natural immunity to the sneak-path issue of crossbar logic circuits—are believed to be capable of significantly advancing both our understanding and commercialization of related logic circuits. Moreover, peculiar CRS cells have been demonstrated to be feasible for tri-level storage, which can serve as an alternative method of realising ultra-high-density data storage.

Unipolar resistive switching with forming-free and self-rectifying effects in Cu/HfO2/n-Si devices

One of the most effective methods integrating self-rectifying RRAM is alleviating sneak current in crossbar architecture. In this work, to investigate RRAMs with excellent properties of self-rectifying effect, simple Cu/HfO2/n-Si tri-layer devices are fabricated and investigated through I − V characteristic measurement. The experimental results demonstrate that the device exhibits forming-free behavior and a remarkable rectifying effect in low resistance state (LRS) with rectification ratio of 104 at ±1 V, as well as considerable OFF/ON ratio (resistive switching window) of 104 at 1 V. The formation and annihilation of localized Cu conductive filament plays a key role in the resistive switching between low resistance state (LRS) and high resistance state (HRS). In addition, intrinsic rectifying effect in LRS attributes to the Schottky contact between Cu filament and n-Si electrode. Furthermore, satisfactory switching uniformity of cycles and devices is observed. As indicated by the results, Cu/HfO2/n-Si devices have a high potential for high-density storage practical application due to its excellent properties.

Microstructural and Mechanical Properties of TiAlN and Ti3AlN Films Deposited by Reactive Magnetron Sputtering

Two series of TiAlN and Ti3AlN films have been deposited on Si (100) substrates by reactive magnetron sputtering TiAl and Ti3Al targets in Ar/N2 mixture. The effects of incoming ions energies controlled by Vb on the microstructure, morphologies, residual stress and hardness have been explored by XRD, SEM, AFM, surface profiler and nanoindentation. The results showed that single phase cubic Ti-Al-N solid solubility formed by Al atoms replacing some Ti atoms in the cubic TiN lattice occured in both TiAlN and Ti3AlN films. As substrate bias increased, the preferred orientation firstly changed from (111) to (200), and then returned to (111) at higher substrate bias. At the same time, high substrate bias promoted the densification of films and presence of high compressive stress, which is benefit for improvement of hardness.

Effect of Spark Plasma Sintering Temperature on the Consolidation of SiC Fiber Reinforced Titanium Alloy Matrix Composites

Continuous SiC fiber reinforced titanium alloy matrix composite (SiCf/Ti) is a potential material in aeronautical field for its excellent mechanical properties. In this work, continuous SiC fiber reinforced TC17 alloy composites (SiCf/TC17) were fabricated by spark plasma sintering (SPS) at different sintering temperatures from 800 to 1000 oC with interval of 50 oC. Consolidated samples were investigated by SEM, EDS and Matrix erosion method. The results showed that the densification degree and the thickness of the interfacial reaction layer increased as the sintering temperature elevated. In addition, the interface reaction layer with typical tooth shape microstructure mainly consisted of TiC and TixSiy, which was quite similar to t that of hot isostatic pressing (HIP) sample. Due to the aggravation of interfacial reaction, there were lots of voids around interfacial layer above 1000 oC, and the residual stress was hardly affected by the sintering temperature. The SiCf/Ti composites can be consolidated at a lower temperature using SPS technology compared with the HIP processing, which is beneficial to the control of the interface reaction together with the reducing of the cost.

Investigation of Interface in SiC Fiber Reinforced TC17 Titanium Alloy Matrix Composites

The investigations were focused on the thermochemical and mechanical properties for interface in continuous SiC fiber reinforced TC17 titanium alloy (nominal composition wt.% is Ti-5Al-2Sn-2Zr-4Mo-4Cr) matrix composites (SiCf/Ti). Scanning electron microscope (SEM), transmission electron microscopy (TEM), and electron probe microanalyzer (EPMA) were applied to observe and analyze the interface reaction product at different heat treatment temperatures. In addition, the reaction rate as well as the relationship between the thickness of reaction layer and time was researched. The interfacial strength at different consolidation temperatures was obtained by means of push-out test, while erosion method was employed to measure the residual stress of composites under different consolidation parameters. The results demonstrate that the thickness of interface reaction layer and heat exposure time is accord with the relationship x=kt1/2+x0, and the interface strength is correlated with the thickness of interface reaction layer, which increases with the intensity of interface reaction. Through the comparison, we find that the inner residual stress of the sample consolidated at 940 °C is higher than that of 920 °C.

Microstructural Difference between Unreinforced Canning of TC17 Alloy and the Matrix in SiCf/TC17 Composite Fabricated by HIP Process

Continuous unidirectional SiCf/TC17 composite has been fabricated by hot isostatic pressing (HIP). After consolidation, the TC17 canning (the unreinforced ambient portion of the specimen) showed an equiaxed microstructure, whereas the matrix of SiCf/TC17 composite (deposited on the continuous SiC fibers by magnetron sputtering) exhibited a typical lamellar structure. In this work, the heat treatments under different condition, XRD, SEM and WDS have been employed to characterize and analyze the microstructural difference. The results indicated that the difference in β transus temperature (Tβ) between the canning and matrix of TC17 alloy induced the microstructural diversity. The introduction of C element (an intensive α stabilizing element) into the matrix alloy may be ascribed to the diffusion of carbon layer at the surface of SiC fiber. As a result, Tβ of matrix TC17 alloy increased to above 1000 °C, much higher than that of the canning TC17 alloy (890 °C). The investigation of microstructure difference reveals the microstructure evolution in SiCf/TC17 composite, which can provide an effective reference for following processing design.

Effect of Sputtering Current on Growth and Microstructure for Titanium Alloy Coatings onto SiC

The influences of sputtering current on deposition rate, composition, microstructure evolution and growth mechanism for titanium alloy coatings onto SiC fibers are explored by surface profiler, auger electron spectrometer, X-ray diffraction, scanning electron microscopy and atomic force microscope. The experimental results show that crystallization take place in all coatings with hexagonal structure (α-Ti). As sputtering current is increased, deposition rate and Al content increase, and Ti content decreases. Coating growth mode alsotransforms from V-shaped column grains to equiaxed grains as sputtering current increased. The column grains are generally not single grains, and more nanograins are composed