Study On Liquid Phase Sintering Of Laminated PTCR Materials And Modification Of Its Ni Internal Electrode

Due to its high dielectric constant, BaTiO₃ceramics can be used to manufacturepassive devices with good performance. Nowadays, miniaturization, integration andlow operating voltage are the development directions of electronic systems. Therefore,these ceramic devices are also developing to laminate chip type. This work hasstudied on key preparation technologies of chip and laminate positive temperaturecoefficient resistor （PTCR）.Liquid phase can effectively lower the sintering temperature of ceramics, and hasenormous effects on the microstructure, PTC effect and room temperature resistivityof PTCR. SiO₂and BN are two common liquid sintering aid. Compare with SiO₂, BNliquid phase forms at as low as942℃. It can greatly lower the sintering temperatureand increase PTC effect, but also lead to a large grain size and big room temperatureresistivity. The adding of liquid phase sintering aid leads to some phenomena that theold oxygen diffusion model can’t explain. Based on the influence of liquid phase onthe grain size, relative density and electronic characteristic of BaTiO₃ceramic, someclassic theories of powder metallurgy are introduced to explain these phenomena, andthe sintering properties of BaTiO₃ceramic are discussed.The internal Ni electrode is printed before the laminated positive temperaturecoefficient resistors are sintered. These devices are sintered in reducing atmosphereinstead of air because Ni element is easily oxidized in air, and then reoxidized in air.The PTC effect is higher at higher reoxidization temperature, but the roomtemperature resistivity is also higher resulting from the oxidization of Ni electrode.It’s a hot topic that uses BaTiO₃to coat Ni powder to improve the inoxidizability ofNi electrode. In this work, hydrothermal method was used to coat Ni powder withBaTiO₃to manufacture Ni electrode with high inoxidizability.