Comparison of Paraelectric and Ferroelectric Materials for Applications as Dielectrics in Thin Film Integrated Capacitors

Ferroelectrics such as BaTiO3, PbxZr1-xTiO3 and BaxSr1-xTiO3 can exhibit dielectric constants up to three orders of magnitude higher than those of paraelectric materials such as SiO2, Al2O3, Ta2O5, and BCB. However, the dielectric properties of ferroelectrics are typically a stronger function of temperature, frequency, film thickness, and bias resulting in significant nonlinearities in their performance. Also, the dielectric constant of some ferroelectrics degrades with time. As a result, paraelectrics are more suitable for hightolerance applications such as filtering, timing, RF/wireless, and A/D where constant, predicable capacitance is required. Ferroelectrics would be preferred for decoupling due to their higher dielectric constants and due to the fact that less tolerance is necessary; the capacitor only needs to meet a certain minimum value. Either might be used for termination as long as footprint requirements can be met. Annealing temperatures for high-k ferroelectrics are currently excessive for applications on organic boards which complicate their integration into these substrates. Since capacitor values on a single board might span up to six orders of magnitude, it may be necessary to use more than one dielectric material to restrict the capacitor footprints to an acceptably smaller range. BCB and SiO2 may be more useful for these low values and may be already present on the substrate as an interlayer dielectric.