Scaling Organic Electrochemical Transistors Down to Nanosized Channels

The perspective of downscaling organic electrochemical transistors (OECTs) in the nanorange is approached by depositing poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on electrodes with a nanogap designed and fabricated by electromigration induced break junction (EIBJ) technique. The electrical response of the fabricated devices is obtained by acquiring transfer characteristics in order to clarify the specific main characteristics of OECTs with sub‐micrometer‐sized active channels (nanogap‐OECTs). On the basis of their electrical response to different scan times, the nanogap‐OECT shows a maximum transconductance unaffected upon changing scan times in the time window from 1 s to 100 µs, meaning that fast varying signals can be easily acquired with unchanged amplifying performance. Hence, the scaling down of the channel size to the nanometer scale leads to a geometrical paradigm that minimizes effects on device response due to the cationic diffusion into the polymeric channel. A comprehensive study of these features is carried out by an electrochemical impedance spectroscopy (EIS) study, complemented by a quantitative analysis made by equivalent circuits. The propagation of a redox front into the polymer bulk due to ionic diffusion also known as the “intercalation pseudocapacitance” is identified as a limiting factor for the transduction dynamics.     

Structured graphene devices for mass transport

The reversible atomic-mass transport along graphene devices has been achieved. The motion of Al and Au in the form of atoms or clusters is driven by applying an electric field between the metal electrodes that contact the graphene sheet. It is shown that Al moves in the direction of the applied electric field whereas Au tends to diffuse in all directions. The control of the motion of Al is further demonstrated by achieving a 90° turn, using a graphene device patterned in a crossroads configuration. The controlled motion of Al is attributed to the charge transfer from Al onto the graphene so that the Al is effectively charged and can be accelerated by the applied electric field. To get further insight into the actuation mechanism, theoretical simulations of individual Al and Au impurities on a perfect graphene sheet were performed. The direct (electrostatic) force was found to be ～1 pN and dominant over the wind force. These findings hold promise for practical use in future mass transport in complex circuits.     

直流电作用下Cu在Sn熔体中的溶解动力学以及界面反应

目的 在微观尺度上解析直流电场对金属液/固界面溶解动力学和界面反应的本征影响。方法 在237～312℃温度范围内对电流作用下Cu/Sn/Cu液固界面进行显微结构的表征及溶解动力学的计算。结果 施加直流电时,Cu的溶解速率在阴极端显著增大,而在阳极端则受到抑制。相应地,由于Cu的迁移速度较快,大量阴极Cu迁移至阳极端,使其附近形成大量的金属间化合物。计算了10 A电流作用下阴极Cu的溶解激活能,其数值约为不通电流情况下的一半。结论 直流电的施加显著降低了Cu在Sn熔体中的溶解激活能,而电迁移力是促进Cu扩散的主要原因。     

管脚无铅覆层的Sn晶须问题

Sn镀层表面在某些情况下会长出长达数百微米的晶须,在电子器件服役过程中会导致电路短路等严重的可靠性问题。目前普遍认为内部压应力是导致Sn晶须生长的主要动力之一;晶须生长所需的Sn原子主要以扩散方式或位错运动方式提供,而温度因素既影响原子扩散速度,又影响镀层的应力松弛。预镀Ni或者预先热处理以形成扩散阻挡层来抑制晶须生长的方法较为常用。温度循环是加速晶须生长的一种有效手段。     

ULSI中Cu互连线的显微结构及可靠性

观察了ULSI中大马士革结构的Cu互连线的晶粒生长和晶体学取向.分析了线宽及退火对Cu互连线显微结构及电徙动的影响.Cu互连线的晶粒尺寸随着线宽的变窄而减小.与平坦Cu膜相比,Cu互连线形成微小的晶粒和较弱的 (111) 织构.300℃、30min退火促使Cu互连线的晶粒长大、(111) 织构发展,从而提高了Cu互连线抗电徙动的能力.结果表明,Cu的扩散涉及晶界扩散与界面扩散,而对于较窄线宽的Cu互连线,界面扩散成为Cu互连线电徙动失效的主要扩散途径.     

Electromigration-induced failures in thin-film Al-Cu conductors

The effect of CuAl₂ precipitates on the electromigration lifetime of thin film Al-Cu conductors was studied by varying the Cu concentration in the 0–12 wt per cent range. Experiments show that the conductor lifetime does not increase monotonically with an increase in precipitate content. It is shown that the precipitates, when present in sufficient quantity, can greatly modify the grain size distribution and hence can affect the electromigration lifetime. These results are interpreted in terms of a model relating the vacancy and the copper atom flux along the grain boundaries. The roles of annealing treatments, copper concentration, structural non-homogeneities and test temperatures are explained by the present model.     

MOS VLSI可靠性浅析

本文论述了ＭＯＳＶＬＳＩ主要失效机理，即薄氧化层击穿，热载流子效应，铝－硅接触失效，电迁移以及软错误，并给出了预防上述失效的一些技术措施。     

Electromigration in eutectic SnAg solder reaction couples with various ambient temperatures and current densities

The electromigration behavior of eutectic SnAg solder reaction couples was studied at various temperature (25 and 120℃)when the current density was held constant at 10~4 A/cm~2 or 5×10~3 A/cm~2. Under the current density of 10~4 A/cm~2, scallop type Cu_6Sn_5 spalls and migrates towards the direction of electron flow at room ambient temperature (25℃), but transforms to layer type Cu_3Sn and leaves Kirkendall voids in it at high ambient temperature (120℃). Under the current density of 5×10~3 A/cm~2 plus room ambient temperature,no obvious directional migration of metal atoms/ions is found. Instead, the thermal stress induced by mismatch of dissimilar materials causes the formation of superficial valley at both interfaces. However, when the ambient temperature increases to 120℃, the mobility of metal atoms/ions is enhanced, and then the grains rotate due to the anisotropic property of metal atoms/ions is enhanced, and then the grains due to the anisotropic property of β-Sn.     

采用同步辐射源X射线衍射技术原位观测VLSI铝互连线的应力

为研究VLSI金属互连线的应力导致IC器件失效的问题,采用同步辐射源X射线衍射技术,原位测试了VLSI中Al互连线在电迁徙及加热条件下的应力变化.沉积态的Al互连线在室温下为拉应力.退火过程使拉应力逐渐减小,在300~350℃过程中由拉应力转为压应力.在电流密度为(3×10⁵~4×10⁶) A/cm²,275min的电徙动实验过程中,Al互连线阳极端由拉应力转变为压应力,并随后随着电流密度的增加而增加.此外,采用扫描电镜(SEM)观察了Al互连线的电迁徙失效特征及应力释放过程.     

集成电路互连线电迁移建模综述

简要介绍了集成电路互连线建模发展的历史。回顾了曾广泛使用的一维电迁移引起的回流模型。基于原子通量散度的概念,电迁移建模可以分为两种方法。一种是常用的扩散路径法,该方法能够解释传统的铝片上金属互连的许多重要电迁移现象。然而,随着芯片尺寸越来越小,工业界为了追求更好的性能,转向了使用铜/低k组合作为互连材料,同时引进了三维集成电路技术。顺应这种趋势,第二种驱动力电迁移建模方法发展了起来,该方法有助于人们理解窄互连工艺中的许多现象。有限元模拟也越来越多地用于驱动力分析法。