摘要
本文针对不同结构、尺寸的石墨烯场效应晶体管(graphene field effect transistors,GFET)开展了基于10 keV-X射线的总剂量效应研究.结果表明,随累积剂量的增大,不同结构GFET的狄拉克电压VDirac和载流子迁移率μ不断退化;相比于背栅型GFET,顶栅型GFET的辐射损伤更加严重;尺寸对GFET器件的总剂量效应决定于器件结构;200 μm×200 μm尺寸的顶栅型GFET损伤最严重,而背栅型GFET是 50 μm×50 μm尺寸的器件损伤最严重.研究表明:对于顶栅型GFET,辐照过程中在栅氧层中形成的氧化物陷阱电荷的积累是VDirac和μ降低的主要原因.背栅型GFET不仅受到辐射在栅氧化层中产生的陷阱电荷的影响,还受到石墨烯表面的氧吸附的影响.在此基础上,结合TCAD仿真工具实现了顶栅器件氧化层中辐射产生的氧化物陷阱电荷对器件辐射响应规律的仿真.相关研究结果对于石墨烯器件的抗辐照加固研究具有重大意义.
Abstract
In this paper,the total dose effects of graphene field-effect transistors(GFETs)with different structures and sizes are studied.The irradiation experiments are carried out by using the 10-keV X-ray irradiation platform with a dose rate of 200 rad(Si)/s.Positive gate bias(VG = +1 V,VD = VS = 0 V)is used during irradiation.Using a semiconductor parameter analyzer,the transfer characteristic curves of top-gate GFET and back-gate GFET are obtained before and after irradiation.At the same time,the degradation condition of the dirac voltage VDirac and the carrier mobility μ are extracted from the transfer characteristic curve.The experimental results demonstrate that VDirac and carrier mobility μ degrade with dose increasing.The depletion of VDirac and carrier mobility μ are caused by the oxide trap charge generated in the gate oxygen layer during X-ray irradiation.Compared with the back-gate GFETs,the top-gate GFETs show more severely degrade VDirac and carrier mobility,therefore top-gate GFET is more sensitive to X-ray radiation at the same cumulative dose than back-gate GFET.The analysis shows that the degradation of top-gate GFET is mainly caused by the oxide trap charge.And in contrast to top-gate GFET,oxygen adsorption contributes to the irradiation process of back-gate GFET,which somewhat mitigates the effect of radiation damage.Furthermore,a comparison of electrical property deterioration of GFETs of varying sizes between the pre-irradiation and the post-irradiation is made.The back-gate GFET,which has a size of 50 μm×50 μm,and the top-gate GFET,which has a size of 200 μm×200 μm,are damaged most seriously.In the case of the top-gate GFET,the larger the radiation area,the more the generated oxide trap charges are and the more serious the damage.In contrast,the back-gate GFET has a larger oxygen adsorption area during irradiation and a more noticeable oxygen adsorption effect,which partially offsets the damage produced by irradiation.Finally,the oxide trap charge mechanism is simulated by using TCAD simulation tool.The TCAD simulation reveals that the trap charge at the interface between Al2O3 and graphene is mainly responsible for the degradation of top-gate GFET property,significantly affecting the investigation of the radiation effect and radiation reinforcement of GFETs.
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