高温传感器用的压电晶体衬底及其石墨烯膜电极的制备与性能研究

Piezoelectric crystals that can function at high temperatures without failure are desired for structural health monitoring and/or nondestructive evaluation of the next generation turbines, more efficient jet engines, steam, and nuclear/electrical power plants in artificial intelligence. The present research focuses on the theoretical study and experimental verification regarding the growth and property characterization of high-quality piezoelectric crystals and its graphene electrode for high temperature sensors. LGT (La3Ga5.5Ta0.5O14) crystal will be grown by the Czochralski method and the graphene film electrode will be grown by CVD method. The relationship between the growth conditions and the microstructures and properties of LTG crystals will be carefully studied. It is expected that large size (≥4〞) LGT crystal with low stress and uniform composition can be obtained. Theoretical studies and evaluation of temperature-dependent piezoelectric properties with diverse cutting orientations will be done. The direct deposition of large-area, uniform graphene film electrodes on LGT substrates with specific cutting orientation will be done by the catalyst-free atmospheric-pressure plasma enhanced chemical vapor deposition (PECVD). Meanwhile, the combination of a first colloidal graphene solution deposition on LGT substrates and a subsequent thermal treatment will be used to prepare the graphene film electrodes. The LGT substrate can allow to be heated to high temperature above 1000 ℃, which can enable to deposit high quality graphene film with good crystallinity and excellent electrical and thermal conductivities. Since the graphene film processes excellent elastic, thermal, electrical, and mechanical properties, both the graphene film electrode and its interface to the LGT substrate is much more stable than that of traditional conductive film such as Au. The LGT-graphene complex sensing elements with simple structure, fast response time, and ease of integration in this study all give high-temperature piezoelectric sensor application an advantage and make them of particular interest.

项目将围绕人工智能发展对高性能传感器提出的迫切需求，针对面向高温服役的压电传感元件存在的材料和界面稳定性的难题，采用理论研究分析与实验验证相结合的方法，开展压电单晶衬底、石墨烯膜电极、以及单晶衬底和石墨烯膜层间耦合效应的研究。突破大尺寸(≥4英寸)、高成分一致性、低应力的钽酸镓镧（LGT）压电晶体生长技术，阐明LGT晶体及其切型的微结构与性能关系，获得温度适用范围更广、稳定性好的的高电阻率切型的LGT晶片；阐明非金属晶片衬底表面无转移生长石墨烯膜的机制，诠释压电晶体衬底及石墨烯电极之间的层间耦合规律及界面传递机制，攻克在单晶衬底表面生长高导电、高电子迁移率、高散热石墨烯膜的难题；研制温度一致性好的压切型晶片/石墨烯膜电极复合物传感元件。研究成果将对发展满足高温服役条件的高性能传感器具有重要的科学意义和应用价值。

本项目围绕人工智能发展对高性能传感器提出的迫切需求，针对面向高温服役的压电传感元件存在的材料和界面稳定性的难题，采用理论研究分析与实验验证相结合的方法，开展了钽酸镓镧（LGT）、三硼酸氧钙钇（YCOB）等系列压电单晶材料生长及高导热石墨烯膜制备等研究工作。.通过改进多晶原料制备工艺、合理设计温场、优化生长工艺等方式，采用提拉法生长了高质量的1～4英寸LGT晶体，测试表明LGT晶体具有良好的均匀性，较高的结晶质量（摇摆曲线半峰宽为39.6″）和出色的压电性能（d11=7.1pC/N）。同时通过完善晶体后处理工艺来提高LGT的电阻率，处理后LGT晶体电阻率在500˚C时高达2.45*10^8 Ω·cm。解决了高质量大尺寸LGT晶体生长困难的瓶颈问题，获得的晶体能满足高温传感元件的要求。.通过采用提拉法和下降法，成功生长了1～2英寸的铥（Tm）、钬（Ho）离子掺杂的YCOB晶体。其中TmxY1-xCOB (x=0.1,0.3,0.5,0.7,0.9和1)晶体掺杂后无明显偏析（分凝系数为0.9-1），结晶质量良好（摇摆曲线半峰宽为39.6″）。通过光谱测试，验证了Tm和Ho离子掺杂后的YCOB晶体分别可以满足950 nm和2255 nm信号光的QPCPA放大系统的使用需求，同时也为后续应用于激光领域的晶体设计、生长做了较好的铺垫。.采用改进的机械剪切剥离工艺，一步法实现了尺寸可控的氧化石墨烯浆料的高效制备。采用刮刀涂布法制备了氧化石墨烯薄膜，系统地研究了氧化石墨浓度、剪切速率和剪切时间对氧化石墨烯浆料粘度的影响，确定了成膜工艺适宜的浆料粘度范围为~1800−4280mPa·s。通过控制分解速率，优化热退火工艺，制备的石墨烯薄膜的热导率可达1447.0W·m−1·K−1。研究成果发展了石墨烯结构和性能调控的理论和技术，为石墨烯材料及器件的设计提供了实验依据。