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.
Continuity, Legitimacy, and Agricultural Development: Conclusions
This chapter aims at bringing together the principal conclusions of the volume, emphasising some particular aspects and questions. Policy continuity in relation to the late 1980s was rightly defined by the Aylwin government policymakers as an essential instrument for further agricultural growth. But in a democratic environment the Aylwin policies, in part precisely because of their strong element of continuity, could be implemented only if they were perceived as legitimate by the majority of the rural population, and by the poor in particular. This means that substantial improvements in agricultural income distribution, and in the quantity and quality of the social services provided to the rural poor, were unavoidable. In order to achieve legitimacy it was, and is, necessary to introduce changes. A lucid, creative combination of continuity and change was the only guarantee of success for the Aylwin policies, and for those of future democratic administrations. Continuity and legitimacy are the fundamental pillars for democratic agricultural development.