低溫共燒陶瓷的介電性質量測與燒結匹配性研究

Abstract

低溫共燒陶瓷(Low temperature co-fired ceramic, LTCC) 的燒結是決定整個元件特性的關鍵。燒結後的介電常數的評估，及材料配方調整以得到較小的燒結所造成的變異，及獲得較好的燒結匹配，是這篇論文研究的重點。論文包含三個部分：第一部份是提出一個計算在低溫共燒陶瓷元件的介電常數(ε)方法，此計算方法是利用帶通濾波器的第二諧振頻率 (Second Harmonic Frequency,SHF) 與介電常數的關連性。ε-SHF的關係式可透過模擬來得到，加上量測到 BPF 的 SHF，就可以計算出介電常數。這些計算出來的介電常數，與傳統以 pellet 量測到的介電常數非常相近。 第二部分是提出兩個共燒材料，藉由不同軟化點(onset shrinkage temperature, OST) 及結晶溫度 (crystallization temperature ,CRT)，在燒結時互相抑制對方在 X/Y 方向的收縮,以達到 X/Y 方向收縮只有0.2% (最高燒結溫度在 880℃，降低了燒結所造成的變異。OST溫度 (802 ℃到606 ℃)是藉由不同 Na2O (0-1.0wt%)比例添加在 CaO-SiO2 玻璃所控制，而燒結條件也扮演很重要的角色。這兩個材料經由不同 Na2O 比例及燒結條件，會造成不同的燒結收縮率，但所量測到的介電常數卻差異不大，都是在 6 附近。 第三部份探討 LTCC 與 Ni-Cu-Zn ferrite 共燒情形。將Ni-Cu-Zn ferrite 埋入 B2O3-SiO2 中，在塗上銀電極作成電感。發現添加 35wt% Al2O3在B2O3-SiO2中，與加有 2wt% Bi2O3的 Ni-Cu-Zn ferrite 可以克服燒結不匹配造成的翹曲及裂痕，並且將Ni-Cu-Zn ferrite埋入B2O3-SiO2中，可以提高電感的感值與品質因子。

The sintering behavior of low temperature co-fired ceramic (LTCC) is a key to decide the device characteristics. The way to evaluate the electronic characteristics after sintering, and what kind of material composition has better sintering match are the major topics in this paper. This thesis is composed of three parts. In the first one, a method of estimating the dielectric constant (ε) of dielectric layers in LTCC devices was developed. A band-pass filter (BPF) circuit was designed such that its second harmonic frequency (SHF) strongly depended on the ε of the relevant capacitor built in the BPF. The ε–SHF correlation was established by model simulation. The design of the BPF was realized with various dielectric layers, and the measured SHF was used to determine the ε values of the capacitors from the ε–SHF relationship. These ε values were found to be consistent with those of the sintered pellets, prepared with the same dielectrics and process as BPFs. The ε values of the dielectric layers in other LTCC devices were estimated by this method, in which the BPFs made of the same dielectric layers were fired as dummy samples along with the devices. The second part, a new technique developed for the low shrinkage of LTCC is proposed; this technique is based on a self-constraining mechanism, which relies on composite green tapes formed by two laminated glass layers, each of which has a distinct softening point (onset shrinkage temperature, OST) and a crystallization temperature (CRT). Each layer works as a constraining layer for the other layer in a distinct temperature range to prevent excessive linear shrinkage along the layer plane. The OSTs ranging from 802 to 606oC are adjusted by controlling the amount of Na2O (0~1.0 wt%) added to the CaO-SiO2 glass. The OST and CRT of the two glass layers as well as the heating profile have strong effects on shrinkage ratio, the lowest of which is found to be only 0.2% after sintering up to 880oC. The measured dielectric constant of the sintered samples is approximately 6.0 within a narrow variation range even when the samples have a wide range of shrinkage ratios. The last one, inductors using a new LTCC design, that Ni-Cu-Zn ferrite was buried in B2O3-SiO2 glass within the core of spiral silver coil, were fabricated. The inductance and quality factor of inductor with embedded ferrite are larger than that of pure B2O3-SiO2 glass. Ni-Cu-Zn ferrite was incompatible with the B2O3-Si02 glass during the co-firing process due to sintering shrinkage mismatch. The incompatibility was resolved when 35wt% Al2O3 was added into B2O3-SiO2 glass, which produces glass-ceramic, and 2wt% of Bi2O3 was fluxed into the Ni-Cu-Zn ferrite as sintering aid. Addition of 2wt% of Bi2O3 not only enhances the densification, but also increases the permeability of Ni-Cu-Zn ferrite.