Utilizing a shallow trench isolation parasitic transistor to characterize the total ionizing dose effect of partially-depleted silicon-on-insulator input/output n-MOSFETs

We investigate the effects of 60 Co γ-ray irradiation on the 130 nm partially-depleted silicon-on-isolator(PDSOI)input/output(I/O) n-MOSFETs. A shallow trench isolation(STI) parasitic transistor is responsible for the observed hump in the back-gate transfer characteristic curve. The STI parasitic transistor, in which the trench oxide acts as the gate oxide,is sensitive to the radiation, and it introduces a new way to characterize the total ionizing dose(TID) responses in the STI oxide. A radiation enhanced drain induced barrier lower(DIBL) effect is observed in the STI parasitic transistor. It is manifested as the drain bias dependence of the radiation-induced off-state leakage and the increase of the DIBL parameter in the STI parasitic transistor after irradiation. Increasing the doping concentration in the whole body region or just near the STI sidewall can increase the threshold voltage of the STI parasitic transistor, and further reduce the radiation-induced off-state leakage. Moreover, we find that the radiation-induced trapped charge in the buried oxide leads to an obvious front-gate threshold voltage shift through the coupling effect. The high doping concentration in the body can effectively suppress the radiation-induced coupling effect.

Total ionizing dose induced single transistor latchup in 130-nm PDSOI input/output NMOSFETs

Total ionizing dose induced single transistor latchup effects for 130 nm partially depleted silicon-on-insulator(PDSOI)NMOSFETs with the bodies floating were studied in this work. The latchup phenomenon strongly correlates with the bias configuration during irradiation. It is found that the high body doping concentration can make the devices less sensitive to the single transistor latchup effect, and the onset drain voltage at which latchup occurs can degrade as the total dose level rises. The mechanism of band-to-band tunneling(BBT) has been discussed. Two-dimensional simulations were conducted to evaluate the BBT effect. It is demonstrated that BBT combined with the positive trapped charge in the buried oxide(BOX) contributes a lot to the latchup effect.

Total-Ionizing-Dose-Induced Body Current Lowering in the 130 nm PDSOI I/O NMOSFETs

The body current lowering effect of 130 nm partially depleted silicon-on-insulator(PDSOI) input/output(I/O)n-type metal-oxide-semiconductor field-effect transistors(NMOSFETs) induced by total-ionizing dose is observed and analyzed. The decay tendency of current ratio of body current and drain current I_b/I_d is also investigated.Theoretical analysis and TCAD simulation results indicate that the physical mechanism of body current lowering effect is the reduction of maximum lateral electric field of the pinch-off region induced by the trapped charges in the buried oxide layer(BOX). The positive charges in the BOX layer can counteract the maximum lateral electric field to some extent.

Bias dependence of a deep submicron NMOSFET response to total dose irradiation

Deep submicron n-channel metal-oxide-semiconductor field-effect transistors (NMOSFETs) with shallow trench isolation (STI) are exposed to ionizing dose radiation under different bias conditions.The total ionizing dose radiation induced subthreshold leakage current increase and the hump effect under four different irradiation bias conditions including the worst case (ON bias) for the transistors are discussed.The high electric fields at the corners are partly responsible for the subthreshold hump effect.Charge trapped in the isolation oxide,particularly at the Si/SiO 2 interface along the sidewalls of the trench oxide creates a leakage path,which becomes a dominant contributor to the offstate drain-to-source leakage current in the NMOSFET.Non-uniform charge distribution is introduced into a threedimensional (3D) simulation.Good agreement between experimental and simulation results is demonstrated.We find that the electric field distribution along with the STI sidewall is important for the radiation effect under different bias conditions.

Total ionizing dose effect in an input/output device for flash memory

Input/output devices for flash memory are exposed to gamma ray irradiation.Total ionizing dose has been shown great influence on characteristic degradation of transistors with different sizes.In this paper,we observed a larger increase of off-state leakage in the short channel device than in long one.However,a larger threshold voltage shift is observed for the narrow width device than for the wide one,which is well known as the radiation induced narrow channel effect.The radiation induced charge in the shallow trench isolation oxide influences the electric field of the narrow channel device.Also,the drain bias dependence of the off-state leakage after irradiation is observed,which is called the radiation enhanced drain induced barrier lowing effect.Finally,we found that substrate bias voltage can suppress the off-state leakage,while leading to more obvious hump effect.

Impact of substrate bias on radiation-induced edge effects in MOSFETs

This paper investigates the effects of gamma-ray irradiation on the Shallow-Trench Isolation (STI) leakage currents in 180-nm complementary metal oxide semiconductor technology.No hump effect in the subthreshold region is observed after irradiation,which is considered to be due to the thin STI corner oxide thickness.A negative substrate bias could effectively suppress the STI leakage,but it also impairs the device characteristics.The three-dimensional simulation is introduced to understand the impact of substrate bias.Moreover,we propose a simple method for extracting the best substrate bias value,which not only eliminates the STI leakage but also has the least impact on the device characteristics.

Enhanced Radiation Sensitivity in Short-Channel Partially Depleted Silicon-on-Insulator n-Type Metal-Oxide-Semiconductor Field Effect Transistors

The total ionizing dose effects of partially depleted silicon-on-insulator(SOI)transistors in a 0.13𝜈m technology are studied by^(60)Co𝛿-ray irradiation.Radiation enhanced drain-induced barrier lowering(DIBL)under different bias conditions is related to the parasitic bipolar in the SOI transistor and oxide trapped charge in the buried oxide,and it is experimentally observed for short channel transistors.The enhanced DIBL effect manifests as the DIBL parameter increases with total dose.Body doping concentration is a key factor affecting the total ionizing dose effect of the transistor.The low body doping transistor exhibits not only significant front gate threshold voltage shift as a result of the coupling effect,but also great off-state leakage at high drain voltage due to the enhanced DIBL effect.

Enhanced Total Ionizing Dose Susceptibility in Narrow Channel Devices

Total ionizing dose effects of different transistor sizes in a 0.18µm technology are studied by 60Coγ-ray irradiation.Significant threshold voltage shift is observed for the narrow channel devices,which is called the radiation induced narrow channel effect(RINCE).A charge sharing model is introduced to understand the phenomenon.The devices'characteristic degradations after irradiation,such as threshold voltage shift,increase in on-state current under different drain biases and substrate biases,are discussed in detail.Radiation induced oxide trapped charge at the edges of shallow trench isolation plays an important role in the RINCE.Narrow channel devices are susceptible to the total ionizing dose effect.

总剂量辐照效应对窄沟道SOI NMOSFET器件的影响

本文深入研究了130nm Silicon-on-Insulator(SOI)技术下的窄沟道n型metal-oxide-semiconductor-field-effect-transistor(MOSFET)器件的总剂量辐照效应.在总剂量辐照下,相比于宽沟道器件,窄沟道器件的阈值电压漂移更为明显.论文利用电荷守恒定律很好地解释了辐照增强的窄沟道效应.另外,本文首次发现,对于工作在线性区的窄沟道器件,辐照产生的浅沟槽隔离氧化物(STI)陷阱正电荷会增加沟道区载流子之间的碰撞概率和沟道表面粗糙度散射,从而导致主沟道晶体管的载流子迁移率退化以及跨导降低.最后,对辐照增强的窄沟效应以及迁移率退化进行了三维器件仿真模拟,仿真结果与实验结果符合得很好.

0.18μm MOSFET器件的总剂量辐照效应

对0.18μm metal-oxide-semiconductor field-effect-transistor(MOSFET)器件进行γ射线辐照实验,讨论分析器件辐照前后关态漏电流、阈值电压、跨导、栅电流、亚阈值斜率等特性参数的变化,研究深亚微米器件的总剂量效应.通过在隔离氧化物中引入等效陷阱电荷,三维模拟结果与实验结果符合很好.深亚微米器件栅氧化层对总剂量辐照不敏感,浅沟槽隔离氧化物是导致器件性能退化的主要因素.

硅离子注入引入纳米晶对SIMOX材料进行总剂量辐射加固

本研究工作采用硅离子注入和高温退火工艺对SIMOX材料的BOX层进行总剂量辐射加固。辐射实验结果证明了该加固方法的有效性。PL谱和HRTEM图像显示了硅离子注入及退火工艺在材料的BOX层中引入了Si纳米晶,形成电子陷阱能级,有效俘获电子,从而提高了材料BOX层的抗总剂量辐射能力。

深亚微米器件沟道长度对总剂量辐照效应的影响

研究了180 nm互补金属氧化物半导体技术下的器件沟道长度对总剂量辐照效应的影响.在其他条件如辐照偏置、器件结构等不变的情况下,氧化层中的陷阱电荷决定了辐照响应.浅沟槽隔离氧化层中的陷阱电荷使得寄生的侧壁沟道反型,从而形成大的关态泄漏电流.这个电流与沟道长度存在一定的关系,沟道长度越短,泄漏电流越大.首次发现辐照会增强这个电流的沟道长度调制效应,从而使得器件进一步退化.

Gate length dependence of the shallow trench isolation leakage current in an irradiated deep submicron NMOSFET

The effects of gamma irradiation on the shallow trench isolation(STI)leakage currents in a 0.18μm technology are investigated.NMOSFETs with different gate lengths are irradiated at several dose levels.The threshold voltage shift is negligible in all of the devices due to the very thin oxide thickness.However,an increase in the off-state leakage current is observed for all of the devices.We believe that the leakage is induced by the drain-to-source leakage path along the STI sidewall,which is formed by the positive trapped charge in the STI oxide.Also, we found that the leakage is dependent on the device’s gate length.The three-transistor model(one main transistor with two parasitic transistors)can provide us with a brief understanding of the dependence on gate length.

Radiation induced inter-device leakage degradation

The evolution of inter-device leakage current with total ionizing dose in transistors in 180 nm generation technologies is studied with an N-type poly-gate field device (PFD) that uses the shallow trench isolation as an effective gate oxide.The overall radiation response of these structures is determined by the trapped charge in the oxide.The impacts of different bias conditions during irradiation on the inter-device leakage current are studied for the first time in this work,which demonstrates that the worst condition is the same as traditional NMOS transistors.Moreover,the two-dimensional technology computer-aided design simulation is used to understand the bias dependence.