Characterization of thin film tantalum oxide capacitors on polyimide substrates
ABSTRACT Thin film tantalum oxide capacitors were fabricated on flexible
polyimide substrates and characterized. The capacitance and dielectric
constant were found to be independent of frequency from 100 MHz-1 GHz.
The leakage current-voltage (I-V) characteristics of the virgin tantalum
oxide capacitors were erratic. Both current-induced and
temperature-induced annealing effects on virgin capacitors were
observed. It was found that the defects of the capacitors depend, not
only on the tantalum oxide dielectric, but also on the underlying
electrode. Copper particulates embedded in the bottom electrode were the
primary cause of electrical shorts. The conduction mechanism was found
to be ionic. The ionic conduction activation energies are linearly
dependent on the applied electric field, ranging from 0.47 eV for an
electric field of 0.13 MV/cm to 0.38 eV for 0.73 MV/cm
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ABSTRACT: Ferroelectrics such as BaTiO 3 , Pb x Zr 1-x TiO 3 and Ba x Sr 1-x TiO 3 can exhibit dielectric constants up to three orders of magnitude higher than those of paraelectric materials such as SiO 2 , Al 2 O 3 , Ta 2 O 5 , 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 perfor-mance. Also, the dielectric constant of some ferroelectrics degrades with time. As a result, paraelectrics are more suitable for high-tolerance applications such as filtering, timing, RF/wireless, and A/D where constant, predicable capacitance is required. Ferroelec-trics 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 SiO 2 may be more useful for these low values and may be already present on the substrate as an interlayer dielectric.Journal of Microcircuits and Electronic Packaging. 23(172).
- IEEE Electron Device Letters - IEEE ELECTRON DEV LETT. 01/2005; 26(12):885-887.
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ABSTRACT: The effects of substrate heating on the stoichiometry and the electrical properties of pulsed dc reactively sputtered tantalum oxide films over a range of film thickness (0.14 to 5.4 mum) are discussed. The film stoichiometry, and hence the electrical properties, of tantalum oxide films; e.g., breakdown field, leakage current density, dielectric constant, and dielectric loss are compared for two different cases: (a) when no intentional substrate/film cooling is provided, and (b) when the substrate is water cooled during deposition. All other operating conditions are the same, and the film thickness is directly related to deposition time. The tantalum oxide films deposited on the water-cooled substrates are stoichiometric, and exhibit excellent electrical properties over the entire range of film thickness. ``Noncooled'' tantalum oxide films are stoichiometric up to ~1 mum film thickness, beyond that the deposited oxide is increasingly nonstoichiometric. The presence of partially oxidized Ta in thicker (>~1 mum) noncooled tantalum oxide films causes a lower breakdown field, higher leakage current density, higher apparent dielectric constant, and dielectric loss. The growth of nonstoichiometric tantalum oxide in thicker noncooled films is attributed to decreased surface oxygen concentration due to oxygen recombination and desorption at higher film temperatures (>~100 °C). The quantitative results presented reflect experience with a specific piece of equipment; however, the procedures presented can be used to characterize deposition processes in which film stoichiometry can change.Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 01/2005; 23(3):512-519. · 1.43 Impact Factor