Peter Francis Carcia

Perpendicular magnetic anisotropy in Pd/Co thin film layered structures

This letter presents the results of magnetic studies of thin film, periodic, Pd/Co layered structures with ultrathin cobalt (4–13 A). We show that films with Co thicknesses less than 8 A are easy to magnetize along a direction normal to the film surface. The best films have a saturation magnetization of about 500 emu/cm3 and a coercivity of 550 Oe, and thus they are candidates for a vertical magnetic recording medium. We attribute the perpendicular magnetic easy axis in these films to surface anisotropy at Pd/Co interfaces and strain in thin Co layers.

Perpendicular magnetic anisotropy in Pd/Co and Pt/Co thin‐film layered structures

rf sputtered Pd/Co and Pt/Co thin‐film layered structures (LS) have perpendicular magnetic anisotropy, when the Co layer is ultrathin (<8 A in Pd/Co and <14 A in Pt/Co). The Co thickness (T) dependence of the anisotropy energy (Ku∼T) and the effective anisotropy field (HK∼1/T) in Pd/Co LS support an interfacial anisotropy as the source of the perpendicular magnetic easy axis. In contrast, the anisotropy is independent of Co thickness for thin Co layers in Pt/Co LS, and thus the mechanism for the perpendicular easy axis is thought to be different. We describe magnetization, resistivity, and x‐ray diffraction data that consistently support sharper interfaces in Pd/Co LS than in Pt/Co LS.

Perpendicular magnetic anisotropy and magneto‐optical Kerr effect of vapor‐deposited Co/Pt‐layered structures

We prepared by vapor deposition at room temperature thin (500 A) Co/Pt multilayers or layered structures directly onto glass or Si substrates. They show a preferential magnetization perpendicular to the film plane for Co thicknesses below 12 A and a 100% perpendicular remanence for Co thicknesses below 4.5 A. The magnetic anisotropy can be explained by an interface contribution to the anisotropy. We also investigated the magneto‐optical (MO) polar Kerr effect of these multilayers. Because of their excellent magnetic properties and their potentially high oxidation and corrosion resistance, these Co/Pt‐layered structures are very promising candidates for MO recording. The Kerr rotation θk at λ=820 nm for a 35×(4.0 A Co+12.7 A Pt)‐layered structure, which has 100% magnetic remanence, is modest (−0.12°), but the reflectivity R is high (70%), which results in a respectable figure of merit Rθ2k. Furthermore, the Kerr effect increases towards shorter wavelengths and thus favors future higher‐density recording.

Gas diffusion barriers on polymers using Al2O3 atomic layer deposition

Thin films of Al2O3 grown by atomic layer deposition (ALD) were investigated as gas diffusion barriers on flexible polyethylene naphthalate and Kapton® polyimide substrates. Al2O3 ALD films with thicknesses of 1–26nm were grown at 100–175°C. For Al2O3 ALD films with thicknesses ⩾5nm, oxygen transmission rates were below the MOCON instrument test limit of ∼5×10−3cc∕m2∕day. Applying a more sensitive radioactive tracer method, H2O-vapor transmission rates of ∼1×10−3g∕m2∕day were measured for single-sided Al2O3 ALD films with thicknesses of 26nm on the polymers. Ultrathin gas diffusion barriers grown by Al2O3 ALD may enable organic displays and electronics on permeable, flexible polymer substrates.

High-performance ZnO thin-film transistors on gate dielectrics grown by atomic layer deposition

We fabricated high-performance ZnO thin-film transistors on gate dielectrics of HfO2, HfSiOx, and Al2O3, grown by atomic layer deposition (ALD). Devices on HfO2 had a mobility of 12.2cm2∕Vs with a threshold voltage of 2.6V and subthreshold slope of 0.5V∕decade. Device performance on Al2O3 depended on synthesis temperature. For 100nm thick Al2O3, synthesized at 200°C, ZnO devices had a mobility of 17.6cm2∕Vs with a threshold voltage of 6V and less than ∼0.1nA gate leakage at 20V. The overall trends were that devices on Hf oxides had a lower threshold voltage, while the gate leakage current density was lower on Al2O3. Device characteristics for all ALD dielectrics exhibited negligibly small hysteresis, suggesting a low defect density at the interface of ZnO with the gate dielectric.

Gas diffusion ultrabarriers on polymer substrates using Al2O3 atomic layer deposition and SiN plasma-enhanced chemical vapor deposition

Thin films grown by Al2O3 atomic layer deposition (ALD) and SiN plasma-enhanced chemical vapor deposition (PECVD) have been tested as gas diffusion barriers either individually or as bilayers on polymer substrates. Single films of Al2O3 ALD with thicknesses of ≥10 nm had a water vapor transmission rate (WVTR) of ≤5×10−5 g/m2 day at 38 °C/85% relative humidity (RH), as measured by the Ca test. This WVTR value was limited by H2O permeability through the epoxy seal, as determined by the Ca test for the glass lid control. In comparison, SiN PECVD films with a thickness of 100 nm had a WVTR of ∼7×10−3 g/m2 day at 38 °C/85% RH. Significant improvements resulted when the SiN PECVD film was coated with an Al2O3 ALD film. An Al2O3 ALD film with a thickness of only 5 nm on a SiN PECVD film with a thickness of 100 nm reduced the WVTR from ∼7×10−3 to ≤5×10−5 g/m2 day at 38 °C/85% RH. The reduction in the permeability for Al2O3 ALD on the SiN PECVD films was attributed to either Al2O3 ALD sealing defects in the SiN PE...

Hysteresis, microstructure, and magneto‐optical recording in Co/Pt and Co/Pd multilayers

The factors that influence the coercive field Hc and the shape of the magnetic hysteresis loop for Co/Pt multilayers (MLs), applied as a magneto‐optical (MO) recording medium, have been investigated. The hysteresis loop of MLs, made by evaporation of Kr sputtering, became more rectangular when the total film thickness was reduced, i.e., the saturation field Hs decreased and the nucleation field Hn increased. Hs was calculated using a stripe domain model and Hn was modeled assuming that nucleation took place at a field that destabilized small vestigial magnetic domains. Both models assumed that domain walls can move in the ML film and the agreement with experiment was good. However, these models could not explain the hysteresis loops for the MLs deposited on a thick Pt base layer or made at high sputter gas pressure. These MLs showed a more particulate microstructure and the hysteresis loop was sheared, consistent with magnetic reversal by uniform rotation rather than domain‐wall motion. From thermomagneti...

Particle size effects in thick film resistors

This paper describes the effect of conducting oxide particle size on the electrical conduction properties of thick film resistors based on finely divided Bi2Ru2O7 and Pb2Ru2O6. We show that the critical conduction behavior at low conducting oxide concentration can be described as percolative, and that the conducting threshold is lower for smaller particle size. We also measure an increase in the effective activation energies for the low‐temperature resistivity, as the conducting oxide particle size decreases. This, we show, is consistent with a tunneling model for conduction in thick‐film resistors.

Properties of Pd/Au thin film layered structures

We have synthesized, by rf sputtering, Pd/Au layered structures with periodicities (Pd+Au layers) that vary from 15–95 A. The films have been characterized by x‐ray diffraction. The individual metal layers have (111) orientation perpendicular to the plane of the film. We accurately model the positions and intensities of x‐ray lines by a one‐dimensional diffraction grating of Pd and Au layers and relate the observed x‐ray line widths to loss of long‐range layer coherence induced by dislocations at Pd–Au interfaces. We also find that the in‐plane electrical resistivity of the films varies inversely, and the temperature coefficient of resistance directly with the layer period. We account for both of these trends by considering scattering of electrons from the metal interfaces, using a modified Fuchs theory.

Superconductivity and resputtering effects in rf sputtered YBa2Cu3O7−x thin films

Superconducting stoichiometric YBa2Cu3O7−x films have been grown by rf sputtering of a single bulk material target in an Ar+10% O2 sputtering atmosphere on a variety of substrates. Films on SrTiO3 substrates exhibited the best post‐annealing superconducting properties with the critical onset temperature of 90 K and zero resistance at 67 K. The maximum current density for these samples was 1×105 A/cm2 at 4.2 K. An extensive loss of film underneath the target was observed during the growth of these films which can be attributed to resputtering due to oxygen anion or energetic neutral particle bombardment of the substrate.