基于外场诱导下反铁电厚膜电卡效应的基础研究

The electrocaloric effect has great potential for application in novel solid-state integrated refrigeration devices. Because of the huge electrocaloric effect caused by the enormous entropy change during antiferroelectric-ferroelectric and antiferroelectric-paraelectric phase switching, antiferroelectrics is expected to be used in the new refrigeration devices. Presently, the refrigeration mechanism based on antiferroelectric phase transition is still not clear. Moreover, because of the low temperature reduction in bulk ceramics and low heat capacity in thin films, the study on the electrocaloric effect in antiferroelectrics thick film would have the theoretical and practical values. Therefore, in this project, the optimum fabrication procedure of PbZrO3-based antiferroelectric thick film will first be determined. The effects of composition, density, grain size, growth orientation, electrode materials,thickness and other factors on the breakdown field, dielectric behavior, phase change and heat capacity of the thick films will be investigated. The entropy variation, electrocaloric effect, cooling performance coefficient and refrigeration capacity of the thick films will be explored under the function of electric field and temperature. To optimize the refrigeration behavior, the fatigue mechanism of the electrocaloric effect of the thick films will also be studied. Finally, the refrigeration mechanism in antiferroelectrics will be addressed according to Landau theory. The fulfillment of this work is to provide the experimental and theoretical supports for the applications of antiferroelectric thick film in microelectronic refrigeration devices.

基于电卡效应的致冷行为在新型全固态可集成致冷器件领域有着巨大的实用价值。利用反铁电体在外场诱导发生反铁电-铁电及顺电-反铁电相变时产生的巨大熵变可获得显著的电卡效应，有望在新型致冷器件中得到应用。目前对反铁电体相变致冷机理的研究尚不成熟，且由于块体陶瓷低致冷温度及薄膜材料低热容量的缺点，因此对反铁电厚膜电卡效应的研究将具有理论和应用的双重价值。本项目研究包括：确定PbZrO3基反铁电厚膜制备的优化工艺；研究反铁电厚膜的组成、致密性、晶粒尺度、生长取向、电极材料及厚度等因素对其耐压强度、极化强度、介电行为、相变过程和热容的影响；探究在电场和温度的共同作用下，不同因素对厚膜在相变过程中熵变量、电卡系数、致冷性能系数及热容量的影响；考察厚膜在外场作用下电卡效应的疲劳机理，优化其致冷行为；根据朗道理论，完善反铁电相变致冷机理研究，为推动反铁电厚膜在近室温微电子器件致冷领域的应用奠定实验和理论基础。

随着现代工业技术的飞速发展，微电子系统(MEMS)与超大规模集成电路(ULIC)已逐渐向集成化、小型化、轻量化和多功能化的趋势发展，探索和开发能够与微工作器件进行集成且具有高致冷效率的新型致冷方式和器件具有重要的实际意义。.本项目主要以典型钙钛矿结构的PbZrO3反铁电厚膜作为研究对象。采用PVP改性的sol-gel技术制备PbZrO3基反铁电厚膜。获得了相组成和生长取向可控、结构致密、电学性能良好且厚度为1-10μm厚膜材料，并研究了反铁电厚膜的组成、致密性、晶粒尺度、生长取向、电极材料及厚度等因素对其耐压强度、极化强度、介电行为、相变过程和热容的影响；探究在电场和温度的共同作用下，不同因素对厚膜在相变过程中熵变量、电卡系数、致冷性能系数及热容量的影响；通过对PbZrO3基反铁电厚膜反铁电-铁电和顺电-反铁电相变过程的控制，实现了对其电卡致冷行为的调控。得到了电卡系数ΔT高于10℃、工作温度区间为30-100℃、具有高致冷性能系数及高热容量厚膜材料。开发了一套电卡系数自动测试系统，温度分辨率优于0.1℃，工作区间为室温-200℃。考察厚膜在外场作用下电卡效应的疲劳机理，优化其致冷行为；根据朗道理论，完善反铁电相变致冷机理研究，为推动反铁电厚膜在近室温微电子器件致冷领域的应用奠定实验和理论基础。