Preparation And Properties Of Anodic Bondable LAS Glass-ceramic

Anodic bonding technology is used to bond silicon to the package substrate with an external electric field at a relatively low temperature.It can offer a reliable joint between chips and substrates within a short time,which makes it one of the core technology of 3D integrated packaging of MEMS.Low temperature co-fired ceramic(LTCC)technology can realize the integration of passive components and active device in a module,which is benefit to the miniaturization and multifunctional integration of MEMS devices.Therefore,the study of anodic bondable LTCC material is one of important topics on high-density three-dimensional integrated packaging of MEMS.There are only two reported anodic bondable LTCC material systems: the Pyrex glass/alumina/cordierite system and the Li-Mg-Al-Si-Bi ceramic system.However,due to the high bonding voltage of these two materials,the breakdown of the device and the damage of the microstructure may happen during the bonding process.So,studies on new,low-voltage,anodic bondable LTCC materials are needed to promote the miniaturization and multifunctional integration of MEMS.This thesis studied spodumene glass-ceramics based low-voltage anodic bondable LTCC materials.The main research results are as follows:(1)Thermal properties tailoring of LAS glass-ceramics and the mechanism: LAS glass-ceramics samples with different sodium oxide contents were prepared by sintering method.The main crystal phases of all the investigated LAS glass-ceramic samples are ?-spodumene solid solution,?-spodumene solid solution and zirconia.Sodium oxide can control the crystallinity of LAS glass-ceramics.As the sodium oxide content increases,the crystalline phase/amorphous phase ratio gradually decreases.The research on the sintering properties shows that the addition of an appropriate amount of sodium oxide will promote the sintering of LAS glass-ceramic samples,and the addition of more sodium oxide will deteriorate the sintering properties of LAS glassceramic.The study of the thermal properties reveals that with the increase of sodium oxide content,the thermal expansion coefficient of LAS glass-ceramics gradually increases.The characterization of the Raman spectrum of the material reveals the mechanism by which sodium oxide regulates the thermal expansion coefficient of LAS glass-ceramic materials: 1)The coefficient of thermal expansion between glass phase and crystal phase is different,and sodium oxide can control the crystallinity of LAS glass-ceramics.The change of sodium oxide content leads to the continuous change of the proportion of crystalline phase and amorphous phase in LAS glass-ceramics,resulting in the increase of thermal expansion coefficient of LAS glass-ceramics with the increase of sodium oxide content.2)Sodium oxide,as a glass flux,can promote the generation of non-bridged oxygen,thereby weakening the strength of the glass network,and increasing the thermal expansion coefficient of LAS glass-ceramics.(2)Electrical properties tailoring of LAS glass-ceramics and the mechanism: LAS glass-ceramics samples with different molar ratios of barium oxide were prepared.The results show that with the increase of the content of barium oxide,the crystallization of LAS glass-ceramics is gradually suppressed,and the ratio of crystal phase/amorphous phase is gradually reduced.The substitution of a small amount of barium oxide has a slight effect on the sintering performance of LAS glass-ceramic samples.Substitution of excessive barium oxide will deteriorate the sintering performance of LAS glassceramic materials.As the molar ratio of barium oxide increases,the ionic conductivity and dielectric loss decrease first and then increase.The influence of the molar ratio of barium oxide on the electrical properties of materials can be explained by the percolation network model: when the molar ratio of barium oxide is low,the content of glass phase in the material is low,and it is difficult to form a complete percolation network.The grain boundary mainly plays the role of scattering the charge carriers.Therefore,As the molar ratio of barium oxide increases at first,the electrical conductivity of LAS glass-ceramics gradually decreases.As the molar ratio of barium oxide continues to increase,causing the glass phase content to continue to increase and exceed the threshold,the percolation network will gradually form and the number of percolation path will continue to increase,eventually leading to the increase of ionic conductivity as the molar ratio of barium oxide increases.(3)LAS glass-ceramics substrates suitable for wafer-level vacuum packaging of MEMS were prepared.The via-hole back filling process was developed,which effectively improved the success rate of hole-filling.The co-firing of electrode paste and the substrate in a high-purity nitrogen atmosphere can effectively suppress the diffusion of the silver.The experiment of anodic bonding shows that the substrate made by LAS glass-ceramic can be bonded with silicon at a voltage of 200 V,which can meet the needs of wafer-level vacuum packaging applications.