Capacitance Measurement of Cerium Oxide Thin Film Capacitors

Abstract

IntroductionCerium oxide (CeOx) is an attractive material for large volume on-chip decoupling capacitors, owing to its high dielectric constant (k) of 28. Commonly, a definite frequency dispersion in the small-signal capacitance measurement is observed in the frequency sweep, and larger capacitance values can be obtained at low frequency in the kHz range. The dielectric relaxation is reported to originate from the interface polarization between the polycrystalline grains in the films. In this work, the thickness-dependent polarization and the capacitance measurement under a DC voltage application are characterized.Fabrication processCeOx films with thicknesses from 8 to 20 nm were deposited by e-beam evaporation on an n+Si substrate with a W layer atop. Another W layer was deposited on CeOx layers and patterned to form electrodes. After the Al back contact formation, the samples are annealed at 420oC.ResultsFig. 1 shows the frequency dispersion of the capacitors with different CeOx thicknesses measured at 0 V. The dielectric relaxation frequency shifts to higher frequency while thinning the thickness, which is useful for capacitor application. The transient current upon 1 V application is shown in fig. 2. After a high charge current, one can observe a decay in the transient current, indicating the delay in the polarization. The capacitance of the samples can be obtained by taking the integral of the charge current and is shown in fig. 3. Comparable capacitance values were obtained with the small-signal measurements. 2 to 3 times higher capacitance values can be achieved with respect to the ionic polarization.ConclusionHigh capacitance values measured in the small-signal setup were confirmed by direct current measurement by DC voltage application. An even higher capacitance can be obtained with the thinner film.