微粉末を用いた泳動電着法によるBa_(1-x)Sr_xTiO_3誘電膜の作製と誘電特性の評価

摘要

電子デバイスの小型化　高速化，高機能化が進むにつれて，rn近年，その内蔵素子であるDRAMの記憶部に用いられる誘rn電膜の高容量化が期待されており，ベロブスカイト型構造をrnもつBa_(1-x)Sr_xTiO_3は高い誘電率と低い誘電損失を有しているrnことから誘電膜層として最も適した物質の1つであると考えrnられている。この物質のバルク体は，室温においてSrrn置換量xが0～0.3の範囲にあるときは強誘電体，0.3～1のrn範囲にあるときは常誘電体であり，相境界であるx＝0.3付rn近の組成のときに室温において最も比誘電率（ε_r）が高い結晶rn構造をとることが知られている。%Recently, Ba_(1-x)Sr_xTiO_3, with a perovskite structure, has drawn much attention as a dielectric material. For this study, we prepared Ba_(0.7)Sr_(0.3)TiO_3 films using electrophoretic deposition with Ba_(0.7)Sr_(0.3)TiO_3 fine particles of various sizes. For the film-forming process, we optimized the deposition voltage, deposition time, sample concentration, I_2 concentration, and other parameters. Results show that the film thickness is controllable by changing the deposition time and voltage, although higher voltage made the film inhomogeneous. A film prepared with larger particles seemed to have lower density, but the density was improved using heat treatment at higher temperatures. Investigation of dielectric properties of the films revealed that a Ba_(0.7)Sr_(0.3)TiO_3 film deposited in 0.5 g·L~(-1) I_2-added acetone for 8 s at 50 V with a particle size of 0.3 μm and then heat-treated at 900 ℃ for 30 min had 2.52 μm thickness. It exhibited capacitance density of 113.9 nF·cm~(-2).