片式PTC热敏陶瓷在还原再氧化过程中氧及缺陷行为与导电机理研究

With the rapid development of microelectronics and the surface-mounting technology, integration, miniaturization and chip type of the positive temperature coefficient (PTC) of resistance of thermistor have become the trend of today’s microelectronics technology. The low resistance of the chip-type PTC thermistor has become a research hotspot, they have been widely used in low-voltage circuit for the over-current protection. However, the micro-defects mechanism of the samples reoxidated in air after sintering in a reducing atmosphere is unclear; and study on the behavior of oxygen and defects need to be further. In our previous research, it is difficult to match the low resistivity and the high resistance jump of the samples at the same time, and the resistance jump is not higher than the general. In the study, using the positron annihilation technique (PAT) the behavior of oxygen and defects of the chip-type PTC ceramics could be quantitatively analysis in the process of the reduction and oxidation. The influence of the partial pressure of oxygen, stoichiometry, the donor-dopant and sintering system on the microstructure of the samples will be studied as well. The optimization design ways of adjustable sample formula can be obtained. The micro-defect compensation mechanism of the sample in the process of reduction and oxidation is clarified. The micro-conductive mechanism of the reproduction of PTC effect during the oxidation will be revealed, the results can prepared to the provide theoretical and experimental basis for the multilayer PTC ceramics, and provide a new way of quantitative analysis of the micro-defects and the reasonable formula, in order to solve the contradiction of the low resistance and the high resistance jump of the same sample.

随着微电子技术和表面贴装技术的快速发展，PTC热敏陶瓷元件向着微型化、片式化和集成化方向发展。而低电阻片式PTC热敏陶瓷元件已成为研究的热点，已广泛应用于低压电路的过流保护，然而样品在还原再氧化过程中微观缺陷机制尚未明确；并且在氧及缺陷行为方面的研究有待于进一步地深入。在前期研究中发现该元件的低阻化与高升阻比很难匹配，且升阻比普遍不高。本课题拟采用正电子淹没技术（PAT）定量地分析片式PTC热敏陶瓷在还原再氧化过程中氧及缺陷行为，研究氧分压、化学计量比、施主掺杂量和烧结制式对该样品微观结构的影响，获得样品配方调控优化设计的新途径，阐明样品在还原再氧化过程中微观缺陷补偿机制，揭示再氧化过程中PTC效应再现的微观导电机理及其潜在的变化规律，为多层片式PTC热敏陶瓷的成功制备提供理论与实验依据，也提供一条微观缺陷定量分析与配方合理调控相结合的新思路，以解决该样品低电阻和高升阻比之间的矛盾。

随着微电子技术和表面贴装技术的快速发展，片式PTC热敏陶瓷元件已广泛应用于低压电路的过流保护，然而样品在还原再氧化过程中微观缺陷机制尚未明确；该元件的低阻化与高升阻比很难匹配。本项目采用流延法和还原再氧化烧结工艺制备出片式BaTiO3基PTC热敏陶瓷材料。利用PAT技术和正交实验法研究了化学计量比、掺杂剂和烧结制式对样品电性能的影响，进而对样品的配方进行优化调控设计。还研究了施主掺杂量、烧结温度和再氧化热处理等因素对片式PTC热敏陶瓷的氧及微观缺陷行为的影响。实验表明片式BaTiO3基PTC热敏陶瓷样品的化学计量比（Ba/Ti比）应略大于1，其样品的室温电阻率随着施主掺杂量的增加而呈现出先减小后增大的变化趋势，而升阻比的变化趋势则相反。其次，冷却速率越慢样品的室温电阻就越小，而最佳的冷却速率为每分钟4摄氏度。再次，多层片式PTC陶瓷样品的再氧化温度应控制在850摄氏度以内。最后，我们成功地制备出片式PTC热敏陶瓷样品，其室温电阻和升阻比分别为0.4欧姆和3.5个数量级。此外，我们还获得了样品内氧及微观缺陷行为的信息，明确了该样品在烧结过程中的缺陷补偿机制，为解决低电阻和高升阻比的不匹配矛盾提供科学依据。揭示了片式PTC热敏陶瓷在还原再氧化过程中PTC特性重构的导电机理，为制备多层片式PTC热敏陶瓷奠定理论基础和实验依据。