Reduction Of Effective Dielectric Constant Research Articles

Phase control of magnetron sputtering deposited Gd 2O 3 thin films as high-κ gate dielectrics

Gd 2O 3 thin films as high-κ gate dielectrics were deposited directly on Si(001) substrates by magnetron sputtering at a pressure of 1.3 Pa and different temperatures. X-ray diffraction results revealed that all the films grown from 450 to 570 °C were crystalline, and the Gd 2O 3 thin films consisted of a mixture of cubic and monoclinic phases. The growth temperature was a critical parameter for the phase constituents and their relative amount. Low temperature was favorable for the formation of cubic phase while higher temperature gave rise to more monoclinic phase. All the Gd 2O 3 thin films grown from different temperatures exhibited acceptable electrical properties, such as low leakage current density ( J L) of 10 −5 A/cm 2 at zero bias with capacitance equivalent SiO 2 thickness in the range of 6–13 nm. Through the comparison between films grown at 450 and 570 °C, the existence of monoclinic phase caused an increase in J L by nearly one order of magnitude and a reduction of effective dielectric constant from 17 to 9.

Reduction of effective dielectric constant of gate insulator by low-resistivity electrodes

On metal–oxide–semiconductor capacitors, the effective dielectric constant (keff) values extracted from high-frequency capacitance–voltage measurements were found to decrease when gate electrodes of very low resistivity were used. The equivalent-oxide thickness increase reaches about 1 nm with the low-resistivity electrodes. We examined gate insulators of SiO2, Al2O3, and HfO2 and gate electrodes of Al, TiN, Au, Cr, and TaN. The equivalent-oxide thickness increase can be prevented by inserting a high-resistivity metal film only 0.3 nm thick between the very low-resistivity metal and the insulator. The present results suggest that keff is reduced by the screening of ionic insulators with free electrons of the metal due to a quantum effect.

BaTiO3 thin film capacitors deposited by r.f. magnetron sputtering

Barium titanate, BaTiO3, thin film capacitors were deposited by r.f. magnetron sputtering using a perpendicular arrangement of the substrate with respect to the target. Capacitors with a single-layer amorphous or polycrystal structure, a bilayer structure of amorphous/polycrystal, and a trilayer structure of amorphous/graded polycrystal/polycrystal were extensively investigated. Comparatively, the single-layer amorphous BaTiO3 capacitor demonstrated the highest breakdown voltage (as high as 2.5 × 106Vcm-1) but lowest dielectric constant of around 16. The single-layer polycrystal BaTiO3 capacitor displayed a much higher dielectric constant of above 300 but also revealed high leakage current which in turn reduced the breakdown voltage. By combining the advantages of the amorphous and polycrystal BaTiO3 films, bilayer and trilayer capacitors were produced, yielding superior electrical properties. An optimum thickness for the amorphous layer minimizes the reduction in effective dielectric constant while providing a low d.c. conductivity of 7.0 × 10-11 Ω-1 cm-1 at a bias of 4 V and a high breakdown voltage of 1.9 x 106Vcm-1.

Water Absorption of Resins and Composites: I. Epoxy Homopolymers and Copolymers

Water absorption experiments have been carried out on three DGEBA type epoxy resins. A reactive diluent added to the resin increased water permeation, while a monomer that expanded on cure decreased it. Exposure at 97% relative humidity (RH) gave results that closely paralleled those obtained by water immersion, though the resin had higher solubility for water and lower activation energy for diffusion when immersed, over the temperature range investigated, that is, 23 to 75°C. The activation energy for diffusion was independent of relative humidity, but the diffusion constant was directly proportional to it. The solubility of water was not determined by Henry's law, but instead was determined by relative humidity to the 1.4th power. The water does not appear to be bound to polar groups in the resin, or hydrogen bonding sites, although dielectric tests indicate that it does not behave as free water, since its polarizability is much reduced. The amount of reduction in effective dielectric constant of the water was only about 55 to 77% indicating that there was some clustering of the water molecules in the polymer, rather than complete separation of the molecules.