D. Brassard

Grain size effect on the semiconductor-metal phase transition characteristics of magnetron-sputtered VO2 thin films

Single-phase vanadium dioxide (VO2) thin films have been grown on Si3N4∕Si substrates by means of a well-controlled magnetron sputtering process. The deposited VO2 films were found to exhibit a semiconductor-to-metal transition (SMT) at ∼69°C with a resistivity change as high as 3.2 decades. A direct and clear-cut correlation is established between the SMT characteristics (both amplitude and abruptness of the transition) of the VO2 films and their crystallite size.

Terahertz conductivity of the metal-insulator transition in a nanogranular VO2 film

Terahertz time-domain spectroscopy is used to measure the complex terahertz conductivity of a nanogranular vanadium dioxide (VO2) thin film as a function of temperature through the metal-insulator transition. The Drude–Smith model provides a good fit to the observed terahertz conductivity, revealing a metallic state that forms via switching of individual nanograins and strong carrier confinement within the nanograins due to scattering off grain boundaries. Furthermore, the directly applied Drude–Smith model provides a more accurate description of the measured terahertz conductivity in this material than either Bruggeman or Maxwell–Garnett effective medium theories.

High-k titanium silicate thin films grown by reactive magnetron sputtering for complementary metal–oxide–semiconductor applications

Titanium silicate (TiSixOy) thin films have been successfully deposited by means of radio-frequency magnetron sputtering of a TiO2/SiO2 composite target in a reactive gas atmosphere. The deposition of the films was investigated as a function of the [O2]/([Ar]+[O2]) flow ratio in the 0%–30% range. The bonding states and the dielectric properties of the sputter-deposited TiSixOy films were systematically investigated as a function of the O2 flow ratio. For all the O2 flow ratios studied, Fourier-transform infrared and x-ray photoelectron spectroscopy analyses have clearly revealed the presence of Ti–O–Si type of local environments, which are the fingerprint of the titanium silicate phase. Increasing the O2 proportion in the sputtering chamber was found to cause a significant decrease of the deposition rate and a drastic improvement in the dielectric properties of the films. TiSixOy films exhibiting excellent dielectric properties (i.e., a dielectric constant as high as ∼20, a dissipation factor as low as 0....

Compositional effect on the dielectric properties of high-k titanium silicate thin films deposited by means of a cosputtering process

We report on the successful growth of high dielectric constant (high-k) titanium silicate TixSi1−xO2 thin films of various compositions (0⩽x⩽1) at room temperature from the cosputtering of SiO2 and TiO2 targets. The developed process is shown to offer the latitude required to achieve not only a precise control of the film composition but an excellent morphology (i.e., dense films with low roughness) as well. The Fourier transform infrared and x-ray photoelectron spectroscopy characterizations have evidenced the presence of Ti–O–Si type of atomic environments, which is the fingerprint of the titanium silicate phase. The titanium silicate films are found to exhibit excellent dielectric properties with very low dielectric losses [tan(δ)<0.02] regardless of their composition. The dielectric constant of the films is found to increase with their TiO2 content from 4 (for pure SiO2 films) to 45 (for TiO2). On the other hand, increasing the TiO2 content of the films is also shown to degrade significantly their lea...

Dielectric properties of amorphous hydrogenated silicon carbide thin films grown by plasma-enhanced chemical vapor deposition

The dielectric properties have been determined for stoichiometric amorphous hydrogenated silicon carbide (a-SiC:H) films grown by means of the plasma-enhanced chemical vapor deposition (PECVD) technique. The dielectric constant, dielectric loss, breakdown voltage, and current–voltage (I–V) characteristics of the a-SiC:H PECVD films were systematically determined for various film thicknesses in the 90–1400 nm range. The PECVD a-SiC:H films exhibit not only a dielectric constant as high as 14 but also relatively high breakdown field values around 3 MV/cm. The dielectric constant of the a-SiC:H films was found to remain almost constant over all the investigated frequency range of 1 kHz to 13 MHz, while it decreases as the film thickness is diminished. The analysis of the I–V characteristics of the a-SiC:H films has revealed the existence of two different conduction mechanisms depending on the applied voltages. While exhibiting an ohmic conduction in the low-field region (<0.05 MV/cm), the film conduction at ...

Tuning the electrical resistivity of pulsed laser deposited TiSiOx thin films from highly insulating to conductive behaviors

We report on the successful growth of amorphous TiSiOx thin films by means of pulsed-laser ablation of a TiO2/SiO2 composite target in a high-vacuum chamber. The room-temperature resistivity of the TiSiOx films is found to decrease by more than 6 orders of magnitude (i.e., from ∼2×104 to 10−2 Ω cm) when their substrate deposition temperature (Td) is increased from 20 to 600 °C. On the other hand, by subjecting these films to a post-deposition annealing at 600 °C in oxygen atmosphere, they become highly insulating with a resistivity level as high as 2×1010 Ω cm, regardless of the Td value. The presence of conductive titanium silicide and titanium sub-oxide local phases in the as-deposited TiSiOx films, as revealed by photoelectron spectroscopy analyses, appears to be the cause of the observed tremendous change in the film resistivity. In particular, it is shown that the resistivity of the TiSiOx films is strongly correlated with their oxygen content.

Substrate biasing effect on the electrical properties of magnetron-sputtered high-k titanium silicate thin films

We report on the effect of substrate biasing on the properties of high-dielectric constant (high-k) titanium silicate (TixSi1−xO2) thin films deposited with a room-temperature magnetron-sputtering process. The composition, microstructure, and electrical properties of the TixSi1−xO2 films were systematically characterized, as a function of the substrate bias voltage (VS), by means of various complementary techniques, including x-ray photoelectron spectroscopy, x-ray reflectivity, Rutherford backscattering spectrometry, and appropriate electrical characterizations. We show, in particular, that depositing the TixSi1−xO2 films with a relatively small biasing voltage (VS≈−15 V) leads not only to a significant reduction of their porosity but more interestingly to a marked improvement of their electrical properties. A further increase of the negative bias voltage (from 20 to 110 V) was, however, found to increase progressively the leakage current through the TixSi1−xO2 films. Such a degradation of the electrical...

Pulsed-laser deposition of high-k titanium silicate thin films

We report on the growth of high-k titanium silicate (TiSiO4) thin films by means of the pulsed-laser ablation of a TiO2∕SiO2 composite target. We present a systematic investigation of the effect of the oxygen background pressure [P(O2)] and the substrate deposition temperature (Td) on both the structural and electrical properties of the films. Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed the presence of Ti–O–Si bonds in the films, confirming thereby the formation of the titanium silicate phase. In particular, the P(O2) is shown to be a key factor for controlling the morphology, the oxygen content, and consequently the electrical properties of the titanium silicate films. Indeed, while the films deposited at P(O2)⩾50mTorr present some porosity, a high roughness, and poor dielectric and breakdown field characteristics, those grown at P(O2)<10mTorr and postannealed (at 600°C in O2) are shown to exhibit a dense and smooth microstructure together with excellent...

Thermal behavior of the microstructure and the electrical properties of magnetron-sputtered high-k titanium silicate thin films

We report on the high-temperature stability of high-dielectric-constant (high-k) titanium silicate (Ti0.5Si0.5O2) thin films deposited by means of a magnetron sputtering process. We have investigated the effect of substrate deposition temperature Td (in the 20–600°C range) and postdeposition annealing temperature Ta (in the 200–800°C range) on the electrical, microstructural, and optical properties of the films. The Ti-silicate films grown at room temperature were found to exhibit a combination of excellent electrical properties, including a k-value of 16.5, a leakage current as low as 3nA at 1MV∕cm, and a dissipation factor tan(δ)<0.01. On the other hand, when the processing temperature (Td or Ta) is ⩾300°C, the leakage current of the films is found to degrade progressively. The x-ray diffraction, Raman spectroscopy, and transmission electron microscopy characterizations have shown that the Ti-silicate films exhibit an amorphous microstructure up to a temperature of about 600°C. For higher temperatures, ...

Single-electron tunneling at room temperature in TixSi1−xO2 nanocomposite thin films

Titanium silicate (TixSi1−xO2) nanocomposite thin films containing dispersed TiO2 nanocrystallites have been grown by means of an optimized sol-gel process. The size of the TiO2 nanoprecipitates was varied from ∼1to22nm by controlling the content of the TiO2 component of the films. For the Ti0.40Si0.60O2 film composition, which contains TiO2 nanoparticles of ∼1nm diameter, regular oscillations are observed in their conductance-voltage characteristics in the mid-to-high-fields range. This abnormal behavior can be interpreted by single-electron tunneling at room temperature between the TiO2 nanocrystallites separated by the wider band-gap amorphous TixSi1−xO2 phase.