铁电负电容场效应晶体管研究进展

铁电负电容场效应晶体管可以突破传统金属氧化物半导体场效应晶体管中的玻尔兹曼限制,将亚阈值摆幅降低到60 mV/dec以下,极大地改善了晶体管的开关电流比和短沟道效应,有效地降低了器件的功耗,为实现晶体管特征尺寸的减小和摩尔定律的延续提供了选择.本文分析总结了国内外近年来关于铁电负电容场效应晶体管代表性的研究进展,为进一步研究提供参考.首先介绍了铁电负电容场效应晶体管的研究背景及其意义;然后总结了铁电材料的基本性质和种类,并对铁电材料负电容的物理机制和铁电负电容场效应晶体管的工作原理进行了讨论;接下来从器件沟道材料维度的角度,分别总结了最近几年基于三维沟道材料和二维沟道材料且与氧化铪基铁电体结合的铁电负电容场效应晶体管的研究成果,并对器件的亚阈值摆幅、开关电流比、回滞电压和漏电流等性能的改善进行了分析概述;最后对铁电负电容场效应晶体管目前存在的问题和未来的发展方向作了总结与展望.

相变材料Ge2Sb2Te5的性质及其面向新型数据存储的应用

信息时代产生的海量数据驱动着计算机存储架构的革新,高性能的非易失性存储器和存算一体的神经形态计算成为存储体系的发展方向。首先,介绍了相变材料Ge2Sb2Te5的阻变性质的机理与应用,详细阐述了相变存储器的发展以及神经形态计算的实现。然后,讨论了基于Ge2Sb2Te5铁电性质的存储器、基于Ge2Sb2Te5介电性质的光子存储单元和基于Ge2Sb2Te5应变作用的高迁移率晶体管。最后,讨论了Ge2Sb2Te5和n型硅等材料的异质结结构在器件中的应用。基于Ge2Sb2Te5材料多种特性的新型存储器件必将在未来存算一体的数据处理中扮演重要的角色。

相变材料Ge2Sb2Te5的性质及其面向新型数据存储的应用(续)

3相变材料GST的介电性质及其应用GST的介电性质主要体现在其对光的调控作用,在GST相变过程中伴随的折射率变化可以使其应用于光学存储。不仅是多媒体光盘,GST材料与波导材料结合还可以形成非易失性的光子存储单元。3.1相变材料GST介电性质的机理以正、负电荷中心不重合的电极化方式来传递或记录(存储)电场的作用和影响是材料介电性质的体现。对于应用于光学存储的GST来说,其相变过程中的性质状态,尤其是介电性质会对存储性能产生重要的影响。

Observation of hopping transitions for delocalized electrons by temperature-dependent conductance in silicon junctionless nanowire transistors

We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance characteristics.There are two obvious transition platforms within the critical temperature regimes for the experimental conductance data,which are extracted from the unified transfer characteristics for different temperatures at the gate voltage positions of the initial transconductance gm peak in Vg1 and valley in Vg2. The crossover temperatures of the electron hopping behaviors are analytically determined by the temperature-dependent conductance at the gate voltages Vg1 and Vg2. This finding provides essential evidence for the hopping electron behaviors under the influence of thermal activation and long-range Coulomb interaction.

Influence of dopant concentration on electrical quantum transport behaviors in junctionless nanowire transistors

We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation. Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorus- doped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.

Temperature-dependent subband mobility characteristics in n-doped silicon junctionless nanowire transistor

We have investigated the temperature-dependent effective mobility characteristics in impurity band and conduction subbands of n-doped silicon junctionless nanowire transistors. It is found that the electron effective mobility of the first subband in 2-fold valleys is higher than that of the second subband in 4-fold valleys. There exists a maximum value for the effective subband mobilities at low temperatures, which is attributed to the increase of thermally activated electrons from the ionized donors in the impurity band. The experimental results indicate that the effective subband mobility is temperature-dependent on the electron interactions by thermal activation, impurity scattering, and intersubband scattering.

Transport spectroscopy through dopant atom array in silicon junctionless nanowire transistors

We demonstrate electron transport spectroscopy through a dopant atom array in n-doped silicon junctionless nanowire transistors within a temperature range from 6 K to 250 K. Several current steps are observed at the initial stage of the transfer curves below 75 K, which result from the electron transport from Hubbard bands to one-dimensional conduction band. The current-off voltages in the transfer curves have a strikingly positive shift below 20 K and a negative shift above 20 K due to the electrostatic screening induced by the ionized dopant atoms. There exists the minimum electron mobility at a critical temperature of 20 K, resulting from the interplay between thermal activation and impurity scattering. Furthermore, electron transport behaviors change from hopping conductance to thermal activation conductance at the temperature of 30 K.

Single-electron transport through single and coupling dopant atoms in silicon junctionless nanowire transistor

We investigated single-electron tunneling through single and coupling dopant-induced quantum dots(QDs) in silicon junctionless nanowire transistor(JNT) by varying temperatures and bias voltages. We observed that two possible charge states of the isolated QD confined in the axis of the initial narrowest channel are successively occupied as the temperature increases above 30 K. The resonance states of the double single-electron peaks emerge below the Hubbard band, at which several subpeaks are clearly observed respectively in the double oscillated current peaks due to the coupling of the QDs in the atomic scale channel. The electric field of bias voltage between the source and the drain could remarkably enhance the tunneling possibility of the single-electron current and the coupling strength of several dopant atoms. This finding demonstrates that silicon JNTs are the promising potential candidates to realize the single dopant atom transistors operating at room temperature.

Observation of source/drain bias-controlled quantum transport spectrum in junctionless silicon nanowire transistor

We investigate the influence of source and drain bias voltages(V_(DS))on the quantum sub-band transport spectrum in the 10-nm width N-typed junctionless nanowire transistor at the low temperature of 6 K.We demonstrate that the transverse electric field introduced from V_(DS) has a minor influence on the threshold voltage of the device.The transverse electric field plays the role of amplifying the gate restriction effect of the channel.The one-dimensional(1D)-band dominated transport is demonstrated to be modulated by V_(DS) in the saturation region and the linear region,with the sub-band energy levels in the channel(E_(channel))intersecting with Fermi levels of the source(E_(fS))and the drain(E_(fD))in turn as V_(g) increases.The turning points from the linear region to the saturation region shift to higher gate voltages with V_(DS) increase because the higher Fermi energy levels of the channel required to meet the situation of E_(fD)=E_(channel).We also find that the bias electric field has the effect to accelerate the thermally activated electrons in the channel,equivalent to the effect of thermal temperature on the increase of electron energy.Our work provides a detailed description of the bias-modulated quantum electronic properties,which will give a more comprehensive understanding of transport behavior in nanoscale devices.