Analysis of oxide bulk trapped charge distribution and densities from photo injection characteristics of oxide-nitride-oxide (ONO) structures
The thickness of ONO inter-poly dielectrics dominates the program and erase speed of a flash memory cell transistor with a stack gate structure. Therefore, as flash devices shrink, it is important to prevent the degradation in reliability while scaling down the thickness of the oxide. However, the thickness of the bottom oxide formed on a heavily doped poly-silicon cannot be easily reduced because of its high defect density due to a high concentration of dopants in the floating gate and an enhancement of the oxide thickness caused by oxidation of the doped polysilicon [1]. In order to overcome these problems, advanced LPCVD technology has been introduced, but the LPCVD oxide films still have many defect densities in comparison with thermal oxide films. In this work, the bulk trapped charges distribution and density in the bottom LPCVD oxide were quantitatively investigated by photocurrent-voltage characteristics. In addition, we found that the defect density and distribution in the bottom LPCVD oxide were remarkably decreased using post plasma oxidation.
Determination of insulator bulk trapped charge densities and centroids from photocurrent‐voltage charactersitcs of MOS structures
A new rapid technique for determining the density and centroid of trapped space charge in MOS structures is described. Photocurrent‐voltage characteristics for both the metal‐oxide and Si‐oxide interfaces are used to determine the internal fields due to bulk trapped charge and, hence, its density and centroid. An experimental example of this technique is shown for a MOWOS (metal‐SiO2‐W‐SiO2‐Si) structure where a layer of approximately 1014 W atoms/cm2 deposited 80 or 42 A from the Si‐SiO2 interface and charged by internal photoemission is investigated. This technique is compared to others in terms of its direct, rapid, minimally perturbing, low‐current and low‐field characteristics.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.