고주파 동조 소자 응용을 위한 BST 박막의 제조 및 특성
Fabrication and Characteristic of BST Thin Films for Microwave Tunable Device Applications
고주파 동조소자응용 BST박막 제조;
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(Ba,Sr)TiO_(3)(BST) thin film is also an attractive candidate for microwave and millimeter-wave frequency devices such as varactors, tunable filters and tunable phase shifters because of high tunability (field-dependent change of dielectric constant) and low dielectric loss at microwave frequencies. In this work, BST thin films were prepared by RF magnetron sputtering method. Physical and electrical properties were investigated in BST thin films with various deposition and annealing conditions and different substrates. (Ba,Sr)TiO_(3) thin films were deposited on Pt/Ti/SiO_(2)/Si by RF magnetron sputtering using a multi-component oxide target at various deposition temperatures(RT~650℃), Ar/O_(2) ratio, distance between target and substrate, working pressure, etc. As-deposited thin films were annealed at 650℃ for 30 minutes for further crystallization. C-V tunability and dielectric loss of the BST thin film were greatly dependent on the substrate temperature during deposition even after the films were post-annealed at 650℃. Dielectric constant, tunability and dielectric loss increased with increasing deposition temperature. More stoichiometric (Ba+Sr)/Ti ratio is a major factor for large dielectric constant and tunability in the BST thin film deposited at high temperature. Dielectric loss increased greatly at the deposition temperature above 600℃ because of rough interface between the BST thin film and bottom electrode. Top-electrode annealing at 600℃ reduced dielectric loss significantly. The BST thin film deposited at 600℃ showed the best field-dependent dielectric properties, tunability of 57 dielectric constant of 368 and dielectric loss of 0.018 at 10kHz. The BST thin film on Pt/Ti/SiO_(2)/Si substrate showed larger dielectric constant and tunability than the BST thin film on Pt/Ti/SiO_(2)/Si substrate due to higher (100) preferred orientation.