摘要
为了减少环境污染、打造绿色经济,高效地利用电力变得越来越重要。电力电子设备是实现这一目标的关键技术,已被广泛用于风力发电、混合动力汽车、LED照明等领域。这也对电子器件中的散热基板提出了更高的要求,传统的陶瓷基板如AlN、Al2O3、BeO等的缺点也日益突出,如较低的理论热导率和较差的力学性能等,严重阻碍了其发展。相比于传统陶瓷基板材料,氮化硅陶瓷由于其优异的理论热导率和良好的力学性能而逐渐成为电子器件的主要散热材料。然而,目前氮化硅陶瓷实际热导率还远远低于理论热导率的值,而且一些高热导率氮化硅陶瓷(>150 W/(m·K))还处于实验室阶段。影响氮化硅陶瓷热导率的因素有晶格氧、晶相、晶界相等,其中氧原子因为在晶格中会发生固溶反应生成硅空位和造成晶格畸变,从而引起声子散射,降低氮化硅陶瓷热导率而成为主要因素。此外,晶型转变和晶轴取向也能在一定程度上影响氮化硅的热导率。如何实现氮化硅陶瓷基板的大规模生产也是一个不小的难题。现阶段,随着制备工艺的不断优化,氮化硅陶瓷实际热导率也在不断提高。为了降低晶格氧含量,首先在原料的选择上降低氧含量,一方面可选用含氧量比较少的Si粉作为起始原料,但是要避免在球磨的过程中引入氧杂质;另一方面,选用高纯度的α-Si3N4或者β-Si3N4作为起始原料也能减少氧含量。其次选用适当的烧结助剂也能通过减少氧含量的方式提高热导率。目前使用较多的烧结助剂是Y2O3-MgO,但是仍不可避免地引入了氧杂质,因此可以选用非氧化物烧结助剂来替换氧化物烧结助剂,如YF3-MgO、MgF2-Y2O3、Y2Si4N6C-MgO、MgSiN2-YbF3等在提高热导率方面也取得了非常不错的效果。研究发现通过加入碳来降低氧含量也能达到很好的效果,通过在原料粉体中掺杂一部分碳,使原料粉体在氮化、烧结时处于还原性较强的环境中,从而促进了氧的消除。此外,通过加入晶种和提高烧结温度等方式来促进晶型转变及通过外加磁场等方法使晶粒定向生长,都能在一定程度上提高热导率。为了满足电子器件的尺寸要求,流延成型成为大规模制备氮化硅陶瓷基板的关键技术。本文从影响热导率的主要因素入手,重点介绍了降低晶格氧含量、促进晶型转变及实现晶轴定向生长三种提高实际热导率的方法;然后,指出了流延成型是大规模制备高导热氮化硅陶瓷的关键,并分别从流延浆料的流动性、流延片和浆料的润湿性及稳定性等三方面进行了叙述;概述了目前常用的制备高导热氮化硅陶瓷的烧结工艺现状;最后,对未来氮化硅高导热陶瓷的研究方向进行了展望。
In order to reduce environmental pollution and build a green economy,efficient use of electricity is becoming more and more important. Power electronic equipment is the key technology to achieve this goal,which has been widely used in wind power generation,hybrid vehicles,LED lighting and other fields. This also puts forward higher requirements for heat dissipation substrates in electronic devices. The shortcomings of traditional ceramic substrates,such as AlN,Al2O3 and BeO,are increasingly prominent,such as low theoretical thermal conductivity and poor mechanical properties,which seriously hinder their development. Compared with traditional ceramic substrate materials,silicon nitride ceramics gradually become the main heat dissipation materials for electronic devices due to its excellent theoretical thermal conductivity and good mechanical properties.However,at present,the actual thermal conductivity of silicon nitride ceramics is still far lower than the theoretical value,and some high thermal conductivity silicon nitride ceramics in the world( >150 W/( m·K)) are still in the laboratory stage. The factors affecting the thermal conductivity of Si3N4 ceramics include lattice oxygen,crystal phase and grain boundary equality. Among them,oxygen atom becomes the main factor because the solid solution reaction will occur in the lattice to generate silicon vacancy and cause lattice distortion,which will cause phonon scattering and reduce the thermal conductivity of Si3N4 ceramics. In addition,the thermal conductivity of Si3N4 can also be affected to some extent by crystal phase transformation and crystal axis orientation. And how to realize the mass production of silicon nitride ceramic substrate is also a big problem.At the present stage,with the continuous optimization of the preparation process,the actual thermal conductivity of silicon nitride ceramics is also continuously improved. In order to reduce the oxygen content of lattice,firstly,the oxygen content is reduced in the selection of raw materials.On the one hand,the Si powder with relatively low oxygen content is selected as the starting material,but the introduction of oxygen impurities in the process of ball-milling should be avoided. On the other hand,using high-purity α-Si3N4 or β-Si3N4 as a starting material can also reduce oxygen content. Secondly,selecting appropriate sintering additives can also improve the thermal conductivity by reducing the oxygen content. At present,more sintering additives are Y2O3-Mg O,but oxygen impurities are inevitably introduced,so non-oxide sintering additives can be used to replace oxide sintering additives,such as YF3-MgO,MgF2-Y2O3,Y2Si4 N6C-MgO,MgSiN2-YbF3,etc.,which have also achieved very good results in improving the thermal conductivity. It is found that adding carbon to reduce the oxygen content can also achieve a good effect. By doping some carbon into the raw material powder,the raw material powder is placed in a reductive environment during nitriding and sintering,which promotes the elimination of oxygen. In addition,the thermal conductivity can be improved to some extent by adding seed and increasing sintering temperature to promote crystal phase transformation and by applying magnetic field to make grain grow directionally. In order to meet the size requirements of electronic devices,casting molding has become a key technology for large-scale preparation of silicon nitride ceramic substrates.Starting from the main factors affecting the thermal conductivity,this paper mainly introduces three methods to improve the actual thermal conductivity,such as reducing the oxygen content in the crystal lattice,promoting the crystal phase transition and realizing the orientation of crystal axis. Then,it is pointed out that the casting molding is the key to prepare high thermal conductivity silicon nitride ceramics on a large scale. The sintering process of preparing high thermal conductivity silicon nitride ceramics is reviewed. Finally,the future research direction of silicon nitride high thermal conductivity ceramics is prospected.
作者
廖圣俊
周立娟
尹凯俐
王建军
姜常玺
LIAO Shengjun;ZHOU Lijuan;YIN Kaili;WANG Jianjun;JIANG Changxi(College of Materials Science and Engineering,Shandong University of Technology,Zibo 255049,China)
出处
《材料导报》
EI
CAS
CSCD
北大核心
2020年第21期21105-21114,共10页
Materials Reports
基金
山东省自然科学基金(ZR2016EMM19)
淄博校城融合发展计划(2018ZBXC261)。
关键词
半导体
陶瓷基板
氮化硅
热导率
semiconductor
ceramic substrate
silicon nitride
thermal conductivity
