The microwave properties of Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick film interdigital capacitors on the alumina substrates

Abstract

The crystalline and electrical properties of Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick film interdigital capacitors have been investigated. Screen printing method was employed to fabricate Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick films on the alumina substrates. (Ba,Sr)TiO 3 materials have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (0.01 @ 1 MHz) in the epitaxial thin film form. To improve dielectric properties and reduce sintering temperature, MgO and Li were added, respectively. 10 μm thick films were screen printed on the alumina substrates and then interdigital capacitors with seven fingers of 200 μm finger gap were patterned with Ag electrode. Current–voltage characteristics were analyzed with elevated temperature range. Up to 50 °C, the thick films showed positive temperature coefficient of resistivity (d ρ/d T) of 6.11 × 10 8 Ω cm/°C, then film showed negative temperature coefficient of resistivity (d ρ/d T) of −1.74 × 10 8 Ω cm/°C. From the microwave measurement, the relative dielectric permittivity of Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick films interdigital capacitors were between 313 at 1 GHz and 265 at 7 GHz.