J.-P. Maria

High temperature stability in lanthanum and zirconia-based gate dielectrics

Gate dielectrics composed primarily of lanthana and zirconia were prepared by reactive evaporation. The stability of the layers during high temperature anneals was investigated. By controlling the oxygen partial pressure during heat treatment, lanthana and zirconia films could be protected against reaction with the underlying Si substrate and against the growth of low-e interface layers. The electrical thickness of the dielectrics could be maintained after a 900 °C exposure. The critical oxygen pressure at 900 °C for low-e interface formation beneath ZrO2 and La2O3 dielectrics was ∼2e−4 Torr. The interfaces that formed beneath the ZrO2 and La2O3 layers are distinctly different. The sub-ZrO2 interface, influenced primarily by phase separation, tends towards pure SiO2, while the sub-La2O3 interface, influenced primarily by silicate formation, tends towards a La–Si–O alloy. For both materials, reducing the oxygen pressure to values below 10−7 Torr resulted in rapid degradation of the metal oxide. This dielec...

Crystallization in SiO2–metal Oxide Alloys

HfO 2 -SiO 2 and La 2 O 3 -SiO 2 amorphous alloys were prepared, and their crystallization behavior was studied. The results suggest that higher permittivities can be achieved in the La-containing system without devitrification. The crystallization mechanisms between systems are distinctly different, yet observations are consistent with bulk material. Hf-containing materials tend toward phase separation, while La-containing materials tend toward silicate formation. For Hf-containing films, negligible thickness or time dependence was observed. In La-containing films, rapid thermal anneals could improve crystallization resistance, and thickness effects related to interface reactions were observed. These behaviors are discussed in the context of phase diagrams and metastable immiscibility.

MgO epitaxy on GaN (0002) surfaces by molecular beam epitaxy

We report on the epitaxial deposition of magnesium oxide films with [111] crystallographic orientation on (0002) GaN by molecular beam epitaxy. Specifically, we use an adsorption controlled growth mechanism to initiate the growth process. Electron diffraction shows a spotty intense pattern without intensity fluctuations during growth and evidence of in-plane twinning. X-ray diffraction reveals the films to be epitaxial with full width at half maximum values of 0.3°, 0.5°, and 1° in 2θ, ϕ, and χ circles, respectively. Wet etching of the GaN surface with a HCl:HF mixture prior to growth is critical for achieving high crystalline quality. Epitaxial growth is observed between room temperature and 650°C, with negligible changes in crystalline quality with increased temperature. Atomic force microscopy analysis shows grainy surfaces with feature sizes near 10nm and rms roughness values of 1.4A over 1μm2 areas. X-ray diffraction analysis suggests MgO film stability up to 850°C in ex situ air annealing.

Influence of Pt heterostructure bottom electrodes on SrBi2Ta2O9 thin film properties

The properties of SrBi2Ta2O9 (SBT) films, such as remanent polarization and leakage current density, are closely related to the film/electrode interface and surface roughness of the underlying electrode. SBT films grown on stable Pt/TiO2/SiO2/Si and Pt/ZrO2/SiO2/Si substrates exhibit high remanent polarization, low leakage current density, and low voltage saturation as compared to SBT films synthesized on Pt/Ti/SiO2/Si. It is shown that severe diffusion of Ti from the Ti interlayer onto the surface of the Pt bottom electrode and the increased surface roughness of this electrode stack play key roles in degradation of SBT properties.

Band offsets and growth mode of molecular beam epitaxy grown MgO (111) on GaN (0002) by x-ray photoelectron spectroscopy

MgO is a proposed dielectric for use as a tunneling barrier in devices integrating GaN and ferroelectric oxides. In this study, we present data regarding the growth mode and band offsets of MgO grown epitaxially on GaN (0002) surfaces using molecular beam epitaxy. Using in situ x-ray photoelectron spectroscopy (XPS) and molecular beam epitaxy, we determine, from sequential growth experiments, that the growth of MgO proceeds via the Volmer-Weber (three-dimensional) mode, and full coalescence of the film does not occur until approximately 12nm of MgO has been deposited. The observation of a three-dimensional growth mode is in agreement with previously published data. For the valence band offset, we find a value of 1.2±0.2eV, which corresponds to a 3.2eV conduction band offset. XPS measurements suggest a chemically abrupt interface and no effect on band lineup due to the slow coalescence behavior.

Discrete Barium Strontium Titanate (BST) Thin-Film Interdigital Varactors on Alumina: Design, Fabrication, Characterization, and Applications

Discrete barium strontium titanate (BST) thin-film capacitors in industry standard 0603 footprint are introduced and characterized. BST capacitors have a voltage-dependent permittivity, enabling BST thin-film capacitors to be used as tuning elements in frequency agile devices. The capacitance changed by 1.5:1 at 35 V (116 kV/cm) bias. The temperature dependence of the capacitance was measured to be less than plusmn 20 % from -100 degC to +100 degC. A 2nd-order tunable combline bandpass filter on FR4 substrate has been implemented using the discrete BST varactors. The filter showed a center frequency tuning of 22% from 2.14 GHz to 2.61 GHz upon application of 130 V (433 kV/cm) bias. The zero-bias insertion loss was 4.9 dB which decreased to 2.9 dB at the high bias state. The return loss was better than 11 dB over the tuning range. Nonlinear characterization of the filter using two-tone test and a digitally-modulated CDMA 2000 signal showed an IP3 of +32 dBm and an ACPR of better than -50 dBc up to 26 dBm of input power, respectively

Measurement and calculation of PZT thin film longitudinal piezoelectric coefficients.

The ferroelectric and piezoelectric properties of 2000 {angstrom} thick chemical solution deposited Pb(Zr{sub x}Ti{sub 1{minus}x})O{sub 3} (PZT) thin films were investigated. Several Zr/Ti ratios were studied: 30/70, 50/50 and 65/35, which correspond to tetragonal, near-morphotropic, and rhombohedral symmetries. In all samples, a {l_brace}111{r_brace}-texture is predominant. Longitudinal piezoelectric coefficients and their dc field dependence were measured using the contact AFM method. The expected trend of a maximum piezoelectric coefficient at or near to the MPB was not observed. The composition dependence was small, with the maximum d{sub 33} occurring in the tetragonal material. To explain the results, crystallographic texture and film thickness effects are suggested. Using a modified phenomenological approach, derived electrostrictive coefficients, and experimental data, d{sub 33} values were calculated. Qualitative agreement was observed between the measured and calculated coefficients. Justifications of modifications to the calculations are discussed.

Thermal stability of amorphous LaScO3 films on silicon

The thermal stability of amorphous LaScO3 thin films deposited by molecular-beam deposition directly on (001) Si was investigated by high-resolution transmission electron microscopy (HRTEM), transmission infrared absorption spectroscopy (IRAS), and x-ray diffraction (XRD). IRAS indicated that the as-deposited films contained <0.1A of SiO2 at the interface between LaScO3 and silicon. XRD studies showed that the films remained amorphous after annealing in N2 at 700°C, although HRTEM showed structural order on an ∼1nm length scale even in the as-deposited films. By 800°C, the LaScO3 had started to crystallize and formed a ∼5nm thick Sc-deficient interlayer between it and silicon.

A voltage controlled oscillator using barium strontium titanate (BST) thin film varactor

Barium strontium titanate (BST) has a field-dependent permittivity and can be used as a dielectric in voltage tunable capacitors or varactors. These BST-based varactors are passive devices and have significantly different properties compared to semiconductor varactors. A voltage tunable oscillator using a BST thin film varactor was designed and characterized. The frequency of oscillation varied from 34.8 MHz to 44.5 MHz (28% tuning) upon application of 7 V tuning voltage. The VCO gain was 1.38 MHz/V and the 2nd harmonic was over 23 dB below the fundamental throughout the tuning range.

Thin, crystalline MgO on hexagonal 6H-SiC(0001) by molecular beam epitaxy for functional oxide integration

MgO thin films are proposed as a template for the effective integration of three and four element oxides on wide band gap SiC for next generation multifunctional devices. Oriented, crystalline MgO(111) of 20–380A is grown on 6H-SiC(0001) by molecular beam epitaxy at a substrate temperature of 140°C using a magnesium effusion cell and a remote oxygen plasma source with ion deflection plates located at the end of the plasma discharge tube and approximately 7in. from the sample surface. Films are conformal to the steps of the cleaned SiC surface with a rms roughness of 0.45±0.05nm. Magnesium adsorption controls the growth rate in an excess oxygen environment with Mg:O flux ratios of 1:99–1:20, where the oxygen flux is the equivalent molecular oxygen. The oxygen plasma, which was determined to be free of ions when the ion deflection plates are energized, does impact nucleation and initial stages of the MgO film formation, and there may be evidence of etching mechanisms involved in the thicker film growth. Che...