High Energy Density, High Temperature Capacitors Utilizing Mn-Doped 0.8CaTiO3-0.2CaHfO3 Ceramics

Single layer air co-fired capacitors with Pt internal electrodes were prototyped for the compositions 0.8CaTiO(3)-0.2CaHfO(3) (CHT) and 0.5 mol% Mn-doped 0.8CaTiO(3)-0.2CaHfO(3) (CHT + Mn) to yield a material with a room-temperature relative permittivity of epsilon(r) similar to 170, thermal coefficient of capacitance (TCC) of +/- 15.8% to +/- 16.4% from -50 degrees C to 150 degrees C, and a band gap of similar to 4.0 eV. Impedance spectroscopy revealed that doping with Mn reduces both the ionic and electronic conductivity. Undoped CHT single layer capacitors exhibited ambient energy densities as large as 9.0 J/cm(3), but showed a drastic decrease in energy density above 100 degrees C. When doped with 0.5 mol% Mn, the temperature dependence of the breakdown strength was minimized, and energy densities similar to ambient values (9.5 J/cm(3)) were observed up to 200 degrees C. At 300 degrees C, energy densities as large as 6.5 J/cm(3) were measured. The design rationale for these dielectrics centered on materials with large band gaps, linear or weakly nonlinear permittivities, and high breakdown strengths. These observations suggest that with further reductions in grain size and dielectric layer thickness, the CaTiO3-CaHfO3 system is a strong candidate for integration into future power electronics applications.