AIM:To study the peripheral dose(PD) from highenergy photon beams in radiotherapy using the metal oxide semiconductor field effect transistor(MOSFET) dose verification system.METHODS:The radiation dose absorbed by the...AIM:To study the peripheral dose(PD) from highenergy photon beams in radiotherapy using the metal oxide semiconductor field effect transistor(MOSFET) dose verification system.METHODS:The radiation dose absorbed by the MOSFET detector was calculated taking into account the manufacturer's Correction Factor,the Calibration Factor and the threshold voltage shift.PD measurements were carried out for three different field sizes(5 cm×5 cm,10 cm×10 cm and 15 cm×15 cm) and for various depths with the source to surface distance set at 100 cm.Dose measurements were realized on the central axis and then at distances(1 to 18 cm) parallel to the edge of the field,and were expressed as the percentage PD(% PD) with respect to the maximum dose(dmax).The accuracy of the results was evaluated with respect to a calibrated 0.3 cm3 ionization chamber.The reproducibility was expressed in terms of standard deviation(s) and coefficient of variation.RESULTS:% PD is higher near the phantom surface and drops to a minimum at the depth of dmax,and then tends to become constant with depth.Internal scatter radiation is the predominant source of PD and the depth dependence is determined by the attenuation of the primary photons.Closer to the field edge,where internal scatter from the phantom dominates,the % PD increases with depth because the ratio of the scatter to primary increases with depth.A few centimeters away from the field,where collimator scatter and leakage dominate,the % PD decreases with depth,due to attenuation by the water.The % PD decreases almost exponentially with the increase of distance from the field edge.The decrease of the % PD is more than 60% and can reach up to 90% as the measurement point departs from the edge of the field.For a given distance,the % PD is significantly higher for larger field sizes,due to the increase of the scattering volume.Finally,the measured PD obtained with MOSFET is higher than that obtained with an ionization chamber with percentage differences being from 0.6% to 34.0%.However,when normalize展开更多
This paper investigates gate current through ultra-thin gate oxide of nano-scale metal oxide semiconductor field effect transistors （MOSFETs）, using two-dimensional （2D） full-band self-consistent ensemble Montc Ca...This paper investigates gate current through ultra-thin gate oxide of nano-scale metal oxide semiconductor field effect transistors （MOSFETs）, using two-dimensional （2D） full-band self-consistent ensemble Montc Carlo method based on solving quantum Boltzmann equation. Direct tunnelling, Fowler-Nordheim tunnelling and thermionic emission currents have been taken into account for the calculation of total gate current. The 2D effect on the gate current is investigated by including the details of the energy distribution for electron tunnelling through the barrier. In order to investigate the properties of nano scale MOSFETs, it is necessary to simulate gate tunnelling current in 2D including non-equilibrium transport.展开更多
提出一种用二维器件数值模拟和负偏压温度不稳定性(negative bias temperature instability,NBTI)模型联合计算的方法,分析NBTI效应产生的界面电荷对pMOS器件栅氧化层电场和沟道空穴浓度的反馈作用.通过大量计算和比对分析现有实验得出:...提出一种用二维器件数值模拟和负偏压温度不稳定性(negative bias temperature instability,NBTI)模型联合计算的方法,分析NBTI效应产生的界面电荷对pMOS器件栅氧化层电场和沟道空穴浓度的反馈作用.通过大量计算和比对分析现有实验得出:当NBTI效应产生较多的界面电荷时,由于界面电荷反馈,pMOS器件的NBTI退化将有一定程度的减小.这种退化减小是一种新的退化饱和机制,对不同类型器件的寿命具有不同的影响.在低NBTI器件中,界面反馈对器件寿命曲线的变化影响不大,器件寿命曲线趋向满足指数变化规律.在高NBTI器件中,界面反馈使得寿命曲线变化基本满足幂指数变化规律.展开更多
基金Supported by The Greek Central Council of Health (110Κ/93)
文摘AIM:To study the peripheral dose(PD) from highenergy photon beams in radiotherapy using the metal oxide semiconductor field effect transistor(MOSFET) dose verification system.METHODS:The radiation dose absorbed by the MOSFET detector was calculated taking into account the manufacturer's Correction Factor,the Calibration Factor and the threshold voltage shift.PD measurements were carried out for three different field sizes(5 cm×5 cm,10 cm×10 cm and 15 cm×15 cm) and for various depths with the source to surface distance set at 100 cm.Dose measurements were realized on the central axis and then at distances(1 to 18 cm) parallel to the edge of the field,and were expressed as the percentage PD(% PD) with respect to the maximum dose(dmax).The accuracy of the results was evaluated with respect to a calibrated 0.3 cm3 ionization chamber.The reproducibility was expressed in terms of standard deviation(s) and coefficient of variation.RESULTS:% PD is higher near the phantom surface and drops to a minimum at the depth of dmax,and then tends to become constant with depth.Internal scatter radiation is the predominant source of PD and the depth dependence is determined by the attenuation of the primary photons.Closer to the field edge,where internal scatter from the phantom dominates,the % PD increases with depth because the ratio of the scatter to primary increases with depth.A few centimeters away from the field,where collimator scatter and leakage dominate,the % PD decreases with depth,due to attenuation by the water.The % PD decreases almost exponentially with the increase of distance from the field edge.The decrease of the % PD is more than 60% and can reach up to 90% as the measurement point departs from the edge of the field.For a given distance,the % PD is significantly higher for larger field sizes,due to the increase of the scattering volume.Finally,the measured PD obtained with MOSFET is higher than that obtained with an ionization chamber with percentage differences being from 0.6% to 34.0%.However,when normalize
基金Project supported by the National Key Basic Research Program （Grant No CB302705） and the National Natural Science Foundation of China （Grant No 90307006）.
文摘This paper investigates gate current through ultra-thin gate oxide of nano-scale metal oxide semiconductor field effect transistors （MOSFETs）, using two-dimensional （2D） full-band self-consistent ensemble Montc Carlo method based on solving quantum Boltzmann equation. Direct tunnelling, Fowler-Nordheim tunnelling and thermionic emission currents have been taken into account for the calculation of total gate current. The 2D effect on the gate current is investigated by including the details of the energy distribution for electron tunnelling through the barrier. In order to investigate the properties of nano scale MOSFETs, it is necessary to simulate gate tunnelling current in 2D including non-equilibrium transport.
文摘提出一种用二维器件数值模拟和负偏压温度不稳定性(negative bias temperature instability,NBTI)模型联合计算的方法,分析NBTI效应产生的界面电荷对pMOS器件栅氧化层电场和沟道空穴浓度的反馈作用.通过大量计算和比对分析现有实验得出:当NBTI效应产生较多的界面电荷时,由于界面电荷反馈,pMOS器件的NBTI退化将有一定程度的减小.这种退化减小是一种新的退化饱和机制,对不同类型器件的寿命具有不同的影响.在低NBTI器件中,界面反馈对器件寿命曲线的变化影响不大,器件寿命曲线趋向满足指数变化规律.在高NBTI器件中,界面反馈使得寿命曲线变化基本满足幂指数变化规律.
