医学高频超声用无铅铁电压电单晶复合材料的微加工制备方法和性能调控

The need for improved resolution in developing novel medical high-frequency ultrasound technology prompted intensive demands for high frequency transducers and piezoelectric materials with working frequency from 20 to 80MHz. High kerf width in piezoelectric composite materials fabricated via the traditional dice and fill method limits their applications for higher than 30MHz working frequency. In this project, human and environment friendly lead free ferroelectric piezoelectric single crystals with high piezoelectric performance will be utilized to fabricate high piezoelectric performance and high frequency lead free piezoelectric single crystal / epoxy 1-3 composite materials with micrometer scale kerf width via the lithography and deep reactive ion etching micromachining technology. The key scientific issues will be dealt including the formation mechanism and modulation method of the lead free ferroelectric crystal piezoelectric composite structure with small kerf width, and the scaling effect and modulation method of the ferroelectric domain and piezoelectric properties of the lead free piezoelectric single crystal in the micrometer scale composite materials. The research will deal with the single crystal growth of pure and doped sodium bismuth titanate – barium titanate single crystal with high piezoelectric performance, the lithography and deep etching micromachining of the single crystal composite materials, the modulation method of the piezoelectric property of the composite materials, and the fabrication of high frequency ultrasonic transducer with working frequency over than 40MHz. Thus lead free and high frequency piezoelectric single crystal 1-3 composite materials and high frequency ultrasonic transducer prototype will be provided to meet the demand for novel human friendly medical high frequency ultrasound technology. The research will also provide the instructions for developing novel high frequency lead free piezoelectric materials and micro arrayed ultrasonic transducers.

具有更高分辨率的新型医学高频超声技术迅速发展，对工作频率在20至80MHz的高频超声换能器与无铅压电材料具有迫切需求，传统切割-填充法制备压电复合材料由于刀缝过宽，难于应用于30MHz以上频率。本项目利用高压电性能、对人体和环境友好的无铅铁电压电晶体材料，采用光刻-深反应离子刻蚀微加工技术制备微米尺度缝宽的高性能高频无铅压电单晶/环氧树脂1-3型复合材料，解决低缝宽无铅铁电单晶压电复合结构的形成机制和调控方法、微米尺度下无铅铁电压电单晶的铁电畴与压电性能的变化规律及其调控方法等关键科学问题，通过高压电性能钛酸铋钠-钛酸钡及其掺杂无铅铁电压电单晶生长、无铅单晶复合材料光刻-深刻蚀制备技术及性能调控、40MHz以上高频超声换能器制备等研究，研制出面向对人体友好的医学高频超声领域应用的无铅压电单晶1-3复合材料及高频超声换能器原型器件，并为发展新型高频无铅压电复合材料及微阵列超声换能器提供指导。

具有更高分辨率的新型医学高频超声技术迅速发展，对工作频率在20至80MHz的高频超声换能器与压电材料具有迫切需求，其技术核心在于制备出厚度在微米尺度（20～60微米）、高机电耦合系数、高工作频率的微加工压电复合材料，基于含铅的铌镁钛酸铅（PMN-PT）等弛豫铁电单晶的微加工压电单晶/环氧树脂1-3复合材料，机电耦合系数kt高于70%，能够大幅提升超声成像分辨率，但其存在铅污染问题，本项目利用高压电性能、对人体和环境友好的无铅铁电压电晶体材料研制高工作频率、高性能压电单晶复合材料。本项目采用顶部籽晶溶液法生长出高压电性能钛酸铋钠-钛酸钡（NBBT）、铌酸钾钠（KNN）等无铅铁电晶体，锰掺杂NBBT晶体压电常数d33达到550pC/N，Mn-KNN压电常数d33达300pC/N，机电耦合系数kt达0.64，居里温度达415℃，为微加工压电单晶复合材料制备提供了多种高性能压电组元，并揭示了Fe、Mn掺杂晶体高压电性能的物理机制和结构本质，为发现更高压电效应的压电材料提供理论指导。研究了切割-填充和光刻-深反应刻蚀制备无铅高性能压电晶体复合材料的微加工制备技术，实现了低缝宽压电复合结构调控，研究了微米尺度下铁电畴结构与压电活性的变化规律，并建立了1-3复合压电材料的有限元仿真模型，设计和制备出高频、高性能NBBT无铅压电单晶/环氧树脂1-3型压电复合材料，厚度≤50µm，宽度≤0.5mm，工作频率高于40MHz，机电耦合系数达71%，达到了PMN-PT等含铅压电单晶复合材料性能水平，为发展在血管内超声（IVUS）等医学高频超声技术中应用的无铅高频超声换能器奠定了坚实基础。建立了高频超声换能器的结构设计、器件仿真、以及包含背衬、压电元件、前匹配层的超声换能器制备技术，设计与制备出中心频率达51.8MHz，-6dB带宽为70.2%的Mn-KNN晶体高频超声换能器，实现了血管组织的成像，NBBT压电单晶复合材料机电耦合系数远高于Mn-KNN晶片，采用NBBT压电单晶复合材料制备的高频超声换能器在各种高灵敏度、高分辨率、高频医学超声成像领域具有重要应用价值。