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Fabrication of Highly Functional Potassium Niobate Piezoelectric Thin Films and Its Application to Wide-Band Low-Loss Surface Acoustic Wave Filters

高功能铌酸钾压电薄膜的制备及其在宽带低损耗声表面波滤波器中的应用

基本信息

批准号：
18560302
负责人：
KAKIO Shoji
金额：
$ 2.32万
依托单位：
University of Yamanashi
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

Potassium niobate KNbO_3 (KN) is a promising material for realizing wide-band surface acoustic wave (SAW) filters owing to its large piezoelectric constant. However, it is difficult to grow a large KN single crystal due to the occurrence of several phase transitions. The objects of this study are the epitaxial growth of KN films on LiNbO_3 (LN) substrates and its application to the wide-band and low-loss SAW filters. In this project, the RF-sputtering conditions necessary for obtaining a highly oriented KN thin film, the formation of the epitaxial plane on LN substrate, and the SAW properties on KN/LN structure were investigated.1. The KN thin films were deposited on MgO substrate using several types of target In single-target sputtering with a mixture target of KN:K_2CO_3, as the substrate temperature was decreased, although the K/Nb ratio increased and the (220)-plane spacing approached that of orthorhombic bulk KN, the orientation deteriorated. Using a single K-rich target, K_5NbO_x, a highly (110)-oriented KN thin film with a K/Nb ratio of 0.40 and a (220)-plane spacing near that of orthorhombic bulk KN was obtained by increasing the RF power applied to the O_2-radical source. Moreover, a multigrain structure on the deposited thin films was observed by atomic force microscopy. The displacement current in the oriented KN thin film was observed when an electric field was applied to the interdigital transducer formed on the thin film. This indicates the existence of spontaneous polarization.2. By utilizing L_i_2O out-diffusion technique, an epitaxial plane with a plane spacing close to the (200)-plane spacing of orthorhombic bulk KN was formed on Y-cut LN substrate.3. The analytical results showed that the coupling factor of 35% for a Rayleigh SAW and zero-attenuation for a leaky SAW are obtained on certain cuts of the KN/LN structure.

KNbO_3（KN）具有大的压电常数，是一种很有希望实现宽带声表面波（SAW）滤波器的材料。然而，由于几个相变的发生，很难生长大的KN单晶。本文研究了在LiNbO_3（LN）衬底上外延生长KN薄膜及其在宽带低损耗SAW滤波器中的应用。本课题主要研究了制备高取向KN薄膜所需的射频溅射条件、LN衬底上外延层的形成以及KN/LN结构的声表面波特性.在MgO基片上用几种靶材制备了KN薄膜。在KN：K_2CO_3混合靶单靶溅射中，随着基片温度的降低，虽然K/Nb比增大，（220）晶面间距接近正交晶系体相KN，但取向性变差。采用单一富钾靶K_5NbO_x，通过增加O_2自由基源的射频功率，获得了K/Nb比为0.40、（220）晶面间距接近正交晶系体相KN的高度（110）取向的KN薄膜。此外，沉积的薄膜上的多晶粒结构观察到原子力显微镜。当电场施加到形成在薄膜上的叉指换能器时，观察到取向KN薄膜中的位移电流。这表明存在自发极化.利用Li_2O外扩散技术，在Y切LN衬底上形成了面间距接近于正交晶系体材料KN（200）面间距的外延层.分析结果表明，在KN/LN结构的某些切口上，瑞利声表面波的耦合因子为35%，泄漏声表面波的衰减为零。