為因應現今電子產品輕薄短小之趨勢，積層陶瓷電容(MLCC)之薄層化技術及高介電常數材料為實現高電容化及小型化之主要研究方向。伴隨著介電層的薄層化使電場強度急遽增加，對於鈦酸鋇基陶瓷材料介電層微結構之品質要求愈來愈高。因此如何藉由提升微結構與介電性質相關性之瞭解，進而開發高電容及高可靠度MLCC之介電陶瓷材料為本研究之重點。
本研究首先探討液相燒結控制對(Ba,Ca)(Ti,Zr)O3微結構及介電性質之影響，藉由改變其ABO3鈣鈦礦結構中之A/B計量比及所添加BaO-SiO2玻璃之粒徑，觀察晶體結構、微結構及介電性質之變化及其對產品可靠度之影響。當A/B計量比減少至0.9956時，發現第二相(Ba,Ca)6(Ti,Zr)17O40逐漸產生，其所造成與(Ba,Ca)(Ti,Zr)O3之共晶液相顯著地促進晶粒成長。同時，隨著A/B計量比降低使居里溫度往高溫移動，因而造成室溫介電常數之增加。在晶界上(Ba,Ca)6(Ti,Zr)17O40第二相缺陷之形成造成晶界上電場及應力之改變，這些隨A/B計量比降低所產生之晶界缺陷形成漏電流之管道，因而導致MLCC可靠度變差。此外，添加粒徑較微細BaO-SiO2玻璃之Ba(Ti,Zr)O3陶瓷呈現較均勻之組成分佈及較大之晶粒成長。當玻璃玻璃添加量固定而其粒徑由1200 nm減小至326 nm，隨著玻璃粒徑之減小會促進所添加Mn2+離子之溶入造成晶格體積膨脹，因此抑制正方相轉變為立方相使居里溫度提高。當玻璃粒徑再減小至185 nm，由於均勻晶粒結構之較低正方性，反而使得居里溫度往低溫陡降。本研究發現玻璃扮演的角色不僅只於燒結助劑，更與晶粒成長控制及添加物之傳輸分佈密切相關，並因此造成介電行為之顯著變化。提高玻璃相分佈之均勻性除可有效的提升陶瓷之緻密度之外，更可以極小化玻璃相之添加量，得以降低其所導致之副作用。
第二部分在探討晶核-晶殼結構控制對BaTiO3介電性質之影響，藉由改變鈣含量及添加氧化物之粒徑，觀察其晶核-晶殼微結構變化，並探討其對於介電性質及可靠度的影響。伴隨著(Ba1-xCax)TiO3中鈣含量之增加，會使得晶格體積為之縮小，證明在本研究中較小半徑之Ca離子會佔據BaTiO3晶格中Ba之位置，因而抑制液相燒結及晶粒成長。由於(Ba0.98Ca0.02)TiO3陶瓷粉末呈現較低之正方性，因而在燒結過程中促進添加物之擴散，使得燒結後之晶粒結構大部分被較高正方性之鐵電晶域所佔據，致使其室溫介電常數較BaTiO3陶瓷為之提升約10%高達3009。隨著鈣含量之增加，由A-site陽離子改變所造成之應力變化會致使居里溫度點往高溫移動，有助於提高在高溫下電容之溫度穩定性。當BaTiO3之添加物粒徑由次微米級縮小至奈米級，晶粒間之摻雜物會有效地均勻分散，此時在添加物中之元素會與其BaTiO3之反應增加，進而使晶格體積增加。奈米添加物如MnO及Y2O3之添加不僅促進本身元素之擴散，還包括燒結助劑(Ba0.6Ca0.4)SiO3中之元素如Ca及Si等，可提升其分佈之均勻狀態並可促進其往晶粒之中心均勻地擴散。使燒結後之晶粒結構大部分被具有高正方性之鐵電晶域所佔據，因而得到較高之介電常數。此外，奈米級添加物之添加除可提高生胚薄帶中陶瓷及添加物顆粒之堆積緻密度，減少造成介電層中缺陷所導致短路之機會，更可促進添加物之成分在晶界中之分佈，以降低在晶界中添加物凝聚所造成漏電流路徑之可能性，因此會大幅度地提升MLCCs之良率及其可信賴性。

High performance MLCCs need to possess a high intrinsic dielectric constant (K) and thinner dielectric layers as the market drives electronic devices towards miniaturization and multifunctionality. However, the applied electric field rises significantly with a reduction in dielectric thickness. Microstructures of thinner dielectric layers play a more important role in the development of MLCCs with high capacitance and high reliability.
Effect of various A/B stoichimetry ratio and dimension of BaO-SiO2 glass particles on the microstructure and dielectric properties of BaTiO3 based materials were investigated. XRD results reveal that a second phase of Ba6Ti17O40 formed when the A/B ratio was lower than 0.9956. TEM results show that liquid eutectic BaTiO3-Ba6Ti17O40 affects the sintering behavior and enhances grain growth; the grain size was significantly influenced when the A/B ratio changed from 0.9936 to 0.9976. It was found that with decreasing A/B ratio, the maximum permittivity increased due to a larger grain size, and the Curie point shifted to a higher temperature, which resulted in higher permittivity at room temperature. The highly accelerated life test (HALT) shows that the reliability performance became worse with a decreasing A/B ratio due to the formation of the second phase Ba6Ti17O40 at the grain boundary.
It is found that ceramics doped with finer BaO-SiO2 glass frit have a more homogeneous structure and the mean grain size decreases as the particle size of the glass frit increases. A finer and better spreading glass phase penetrates the BTZ ceramic interface more easily and enhances the grain growth. The extent of the Mn2+ incorporation in BTZ ceramic increases with decreasing glass particle size, from 1200 to 326 nm. The Curie temperature was also shifted accordingly. When the glass particle size is further reduced to 185 nm, the Curie temperature declines significantly due to a more homogeneous grain structure with lower tetragonality. The role of glass is not limited to its use as a sintering aid, but also extended to control the grain growth and dopant transportability, which modify the dielectric properties of ceramics.
The effects of calcium content and nano-sized dopant on the core-shell microstructure and dielectric properties of BaTiO3 were investigated to develop high permittivity ceramic materials for novel X5R/X7R MLCCs. Calcined (Ba0.98Ca0.02)TiO3 powder has lower tetragonality and enhanced diffusion during sintering, thus forming the grain structure dominated by the ferroelectric domain. The Curie temperature rose when the calcium content was increased, which contributed to the capacitance variation at high temperature. The (Ba0.98Ca0.02)TiO3 exhibits around 10% higher permittivity as compared with BaTiO3, due to the dominate ferroelectric grain structure and higher Curie temperature. Predominately ferroelectric core grains were observed in the capacitor doped with nano-sized dopants, and these led to higher capacitance. Nano-sized dopant facilitates the good particle packing of green sheets and reduces defects in the dielectric layers which may lead to initial short circuits. Moreover, the uniform distribution of dopants achieved by adding nano-sized oxide suppresses the agglomeration of impurities in the grain boundaries and also improves the reliability of MLCCs. The reduction of the required amount and uniform distribution of additives using the nano-sized dopant is thus beneficial to the precise control of the core–shell structure for the development of novel X5R MLCCs.

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