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High Temperature, High Energy Density Dielectrics for Power Electronics Applications
Abstract:
Mn and/or rare earth-doped xCaTiO₃ - (1-x)CaMeO₃ dielectrics,
where Me=Hf or Zr and x=0.7, 0.8, and 0.9 were developed to yield
materials with room temperature relative permittivities of
Εr ~ 150-170, thermal coefficients of capacitance (TCC)
of ± 15.8% to ± 16.4% from -50 to 150°C, and band gaps of ~ 3.3-3.6
eV as determined by UV-Vis spectroscopy. Un-doped single layer
capacitors exhibited room temperature energy densities as large as
9.0 J/cm₃, but showed a drastic decrease in energy density above
100°C. When doped with 0.5 mol% Mn, the temperature dependence of
the breakdown strength was minimized, and energy densities similar
to room temperature values (9.5 J/cm₃) were observed up to 200°C.
At 300°C, energy densities as large as 6.5 J/cm₃ were measured.
These observations suggest that with further reductions in grain
size and dielectric layer thickness, the xCaTiO₃ - (1-x)CaMeO₃
system is a strong candidate for integration into future power
electronics applications.
To further improve the high temperature, high field reliability
of these material systems, rare earth donor doping has been
utilized. Initially, 1 mol% doping with Dy, Gd, and Sm showed the
most significant reduction in high temperature, high field
conductivity. Further investigation of Dy co-doping with 0.5 mol%
Mn , Mg, and (Mn+Mg) showed the most significant increase in
Ca(Ti₀.₈Hf₀.₂)O₃ resistivity from 4.61 MΩ.m with only Mn doping
to 176 GΩ.cm with Dy and Mg co-doping. Material systems were
characterized using capacitance and dielectric loss versus
temperature, current-voltage (I-V), UV-Vis spectroscopy for band
gap determination, and polarization versus field measurements.
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