We present a detailed study on the effect of bottom-and top-oxide thicknesses on the current conduction and the dielectric breakdown of oxide/nitride/oxide (ONO) multi-layer dielectrics. An abrupt reduction in current is observed when the oxide that is contiguous to the anode is thicker than 3 nm. This leads us to conclude that the thick oxide (>3 nm) impedes hole injection from anode into nitride. The injected charge-to-breakdown (QBD) and the time-to-breakdown (TBD) are measured to study the breakdown mechanism. We observe that a substantial increase in TBD occurs in spite of the reduction in QBD when the thick oxide is contiguous to anode. This phenomenon is explained by a hole-induced breakdown model for the ONO structure with thin bottom-and top-oxides (<3 nm). Hole injection is suppressed by the thick oxide that is contiguous to anode. The increase in TBD is attributed to the reduction in injected holes. We conclude that the dielectric breakdown of the ONO structure with the thin oxides is induced by injected holes. We also observe that the thermal activation energy of the TSD changes at 3 nm in bottom-oxide thickness under negative gate bias. Therefore, this value of 3 nm is determined as a threshold thickness for the change of the breakdown mechanism.

BackgroundWe investigated a practical method to measure peak filling rate (PFR) as an indicator of diastolic function of the left ventricle. Ten adult volunteers underwent cine MR imaging using steady-state free precession (SSFP) and phase contrast (PC) sequences to measure PFR. Two PC image sets were acquired at the mitral valve orifice, and PFR was determined from the set with high true temporal resolution (temporal PC method) or with high spatial resolution (spatial PC method). SSFP images covering the left ventricle were acquired, and a time–volume curve was generated around the peak filling phase. PFR was determined using parabolic curve fitting on the first-derivative curve of the LV time–volume curve.FindingsPFR values estimated by the PC methods correlated well with those estimated by the SSFP method, despite apparent underestimation. The underestimation was smaller for the temporal PC method (12 %) than for the spatial PC method (28 %). Intra- and inter-observer repeatabilities were better for the PC methods than for the SSFP method.ConclusionsPFR measurement by PC imaging with high true temporal resolution is convenient and offers excellent repeatability and acceptable accuracy, indicating suitability for clinical use.

We evaluated the effective dose (ED) of the CT component of wholebody PET/CT using software dedicated to CT dose estimation and from dose-length product (DLP) values to establish practical methods of ED estimation. Methods: Eighty adult patients who underwent 18 F-FDG whole-body PET/CT were divided into groups A and B, each consisting of 20 men and 20 women. In group A, ED of the CT component was calculated using CT-Expo for 6 anatomic regions separately, and whole-body ED was obtained by summing the regional EDs (CT-Expo method). DLP was calculated for each of the 6 regions and multiplied by a corresponding conversion factor described in International Commission on Radiological Protection publication 102 to obtain the ED for each region (regional DLP method). Whole-body ED was also calculated as the product of a whole-body DLP value provided by the scanner automatically and a conversion factor (simple DLP method). Moreover, the ED/DLP values were calculated using whole-body ED estimated by the CT-Expo method and the scannerderived DLP, to optimize the conversion factor. In group B, the optimized conversion factor was applied for the estimation of ED by the simple DLP method. Results: In group A, the regional DLP method allowed an accurate estimation of mean whole-body ED as a result of counterbalance of mild overestimation in men and mild underestimation in women, regarding the CT-Expo method as a standard. The simple DLP method using a conversion factor for the trunk (0.015 mSv/mGy/cm) caused overestimation. On the basis of the ED/DLP values in group A, a modified conversion factor of 0.013 mSv/mGy/cm and sex-specific conversion factors of 0.012 and 0.014 mSv/mGy/cm for men and women, respectively, were determined. In group B, the use of the modified conversion factor improved accuracy, and the use of sex-specific conversion factors eliminated sex-dependent residual errors. Conclusion: ED of the CT component of whole-body PET/CT can be assessed by multiplying the scannerderived DLP by a conversion factor optimized for whole-body PET/CT. PET with 18 F-FDG has been accepted as a valuable tool in oncology practice. CT images are commonly acquired together with PET images in a single imaging session with an integrated PET/CT scanner (1) and are used for diagnosis on CT images themselves, localization of lesions delineated by PET, and attenuation correction of PET images. The problem of CT acquisition additional to PET is an increase in radiation exposure. The effective dose (ED) derived from the CT component varies widely from 5 to 25 mSv (2-8) and often exceeds the ED from 18 F-FDG injection. Although a large amount of radiation exposure is required to acquire highquality CT images for diagnostic purposes, lesion localization and attenuation correction can be achieved on CT images of lower quality. Dose reduction with preserving clinical utilities should be pursued in each facility considering the purpose of CT and using dose reduction technologies (9,10).Estimation of ED is a prerequisite for optimization and mo...

The appearance of local side etch in polysilicon etching was investigated using a pattern of lines and spaces (L&S) with spaces of various widths. The local side etch is found to appear at lines connected to the silicon substrate even when there is no exposed area of the silicon substrate. It is also found that the degree of local side etch decreases as the area of exposed silicon substrate increases. From these results, it is considered that the cause of the local side etch is the electron supplied from the silicon substrate to polysilicon through the connection, where the source of electrons is, electron irradiation at the sidewall of the lines which have connection and are facing to the wide spaces. The results also show that the electric potential of the silicon substrate in the case when there is no exposed area is lower than the potential of the exposed area of the silicon substrate.

The effects of the “electron shading” charge build-up at the bottom of holes are investigated using fluorocarbon gas plasma. The etch rates of the electrically conductive films such as phosphorus-doped polysilicon at the bottom of the holes change depending on whether the films are patterned or not. This is caused by the decrease of the low-energy ions which reach the bottom of the holes due to positive charging of the underlying layers. Furthermore, the potential at the bottom of the contact holes is investigated using metal-nitride-oxide-silicon (MNOS) capacitors. The positive charging due to the electron shading effect is measured. In order to reduce the electron shading charge build-up, the pulse-modulated plasma is investigated. The selectivity to the underlying layer increases upon using pulse-modulated plasma.