Tony Joseph

SOL‐GEL DERIVED TiSiO4 CERAMICS FOR HIGH‐k GATE DIELECTRIC APPLICATIONS

Homogeneous and stable titanium silicate sols and gels were prepared via the sol‐gel process. TiSiO4 ceramic calcined at 800 °C and sintered at 1275 °C exhibited er = 17.75 and tanδ = 0.042. in the radiofrequency range. The variation of relative permittivity in the operating temperature range (−20 to 70 °C) and thermodynamic stability of the TiSiO4 ceramic with Si powder is also investigated.

Microwave dielectric properties of Ca 5-x Mg x Nb 4 TiO 17 (x = 0–3) ceramics

The Ca_5-xMg_xNb₄TiO₁₇ (x = 0-3) ceramics were prepared by conventional solid state ceramic route. The microstructure of the ceramic was studied using scanning electron spectroscopy. The microwave dielectric properties (Q_uxf, epsiv_r and tau_f) were measured using a vector network analyser. Ca₅Nb₄TiO₁₇ ceramics have a relative permittivity(epsiv_r) of 45, quality factor (Q_uxf) of 17600 GHz (at 4.13 GHz), and coefficient of temperature variation of resonant frequency (tau_f)-113 ppm/degC. The variation in the microwave dielectric properties of Ca₅Nb₄TiO₁₇ ceramics were investigated with the increase in magnesium content. The sintering temperature reduced from 1475degC for x = 0 to 1200degC for x = 3. The quality factor increased with magnesium content and maximum Q_uxf was obtained for the composition x = 2 (22500 GHz (at 3.99 GHz)). The epsiv_r and tau_f of Ca₃Mg₂Nb₄TiO₁₇ ceramics were found to be 37.5 and -4.3 ppm/degC respectively. Hence Ca₃Mg₂Nb₄TiO₁₇ ceramics are very much useful for practical applications like Dielectric resonators in filters and oscillators.

Microwave dielectric properties of Ca 2-x Sr x ZnSi 2 O 7 Ceramics (x = 0–2)

The melilite-type Ca<inf>2–x</inf>Sr<inf>x</inf>ZnSi<inf>2</inf>O<inf>7</inf> ceramics were synthesized by solid state ceramic route. The lattice parameters and cell volume increased with increasing the composition x. The substitution of Sr for Ca has improved the microwave dielectric properties. Excellent dielectric properties (ε<inf>r</inf> = 8.4, Q<inf>u</inf>×f = 105000 GHz (at 12.628 GHz) and τ<inf>f</inf> = −51.5 ppm/°C) were obtained for the composition x = 2 when sintered at 1475°C/2h. Addition of 2wt% of SrTiO<inf>3</inf> to Sr<inf>2</inf>ZnSi<inf>2</inf>O<inf>7</inf> decreased the τ<inf>f</inf> value to −13 ppm/°C with ε<inf>r</inf>= 8.8, Q<inf>u</inf>×f = 60000 GHz (at 12.585 GHz).}