Dielectric properties of diopside-based glass-ceramics and diffusion effect of the co-fired silver electrode
| Autor: | Po-Hsien Wu, 吳柏賢 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Microwave dielectric ceramic materials play an important role in the wireless communications and portable devices, such as global positioning systems (GPS) and mobile phones. This study focuses on a novel microwave dielectric material - diopside (CaMgSi2O6) glass-ceramic. Diopside material has a unique character of low dielectric constant (k), low cost, high quality factor (Q*f value) and lower than 900℃ sintering temperature. Therefore, diopside is a potential candidate material for LTCC (Low Temperature Co-fired Ceramic) process. However, the large temperature coefficient of resonance frequency (τf), -60ppm/℃, is unstable to be applied in microwave dielectric components. In this case, ZnTiO3 was chosen to compensate the large negative temperature coefficient of resonance frequency (τf) of diopside glass-ceramics. Followed by this result, the microstructure analysis and electrode inhibition after co-fired with silver electrode were carried out by SEM-EDS in this work. In the first part of this research, different ratio of ZnTiO3 powder were added into diopside glass-ceramic and the heat treatment were carried out at 825~900℃ for 2 hours. In the beginning, specimens were unable to be densified at 825℃. As increasing heat treatment temperature, the specimens can be densified, from 850℃~ 900℃. Simultaneously, some silicate and titanate secondary phases with excellent microwave dielectric properties were formed, such as (Zn(1-x)Mgx)SiO4 with low dielectric constant and (Zn(1-x)Mgx)TiO3 with positive τf.. Therefore, the microwave dielectric properties of diopside material can be improved by these secondary phases. Finally, the optimal ratio is diopside with 30wt% ZnTiO3 addition, which contains the following key characteristics: k=9.2, Q*f=8232GHz, τf = -17.7ppm/℃ Electrode diffusion usually makes serious damages for components in changing the frequency unexpectedly and overall efficiency of components. Generally, silver ions are oxidized easily then diffuse into diopside glass-ceramics substrate during sintering process. To avoid the phenomena of silver diffusion, a sintering mechanisms without atmosphere control was used. According to references, ceramic phases or amorphous silica are used as both ways can inhibit the electrode diffusion efficiently. As demonstrating in previous chapter, some ceramic phases, silicate or titanate secondary phases, have been formed after adding ZnTiO3 during sintering process, the amorphous silica was chosen to inhibit silver diffusion in this research. Nanoscale amorphous silica forms quartz phase in sintering process around 700℃, and the quartz will become a obstacle for silver diffusion. The efficiency of diffusion effect can be measured by using sem-eds linescan. In conclusion, the optimal solution is to add 4wt% amorphous silica, which diminishes the diffusion effect of silver ions significantly. |
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