Eiji Kusano

Effects of microstructure and nonstoichiometry on electrical properties of vanadium dioxide films

Voided growth structures of sputter‐deposited films affect strongly their optical and electrical properties. Vanadium dioxide is an interesting material to study effects of film microstructure and nonstoichiometry on electrical properties because its phase transition makes it possible to investigate electrical behavior both in a semiconducting phase and in a metallic phase. We have deposited vanadium oxide films with different vanadium/oxygen ratios for substrate temperatures between 250 and 550 °C by dc reactive magnetron sputtering. The resistivity ratios between a semiconducting phase and a metallic phase are limited to 103 order by voided boundaries and oxygen vacancies. The voided boundaries are defined by columnar structure and agglomerated grain growth. The results emphasize the necessity of a combination of deposition to obtain the film with a favorable structure and postdeposition annealing to control the film stoichiometry.

Novel gas sensor using polymer-film-coated quartz resonator for environmental monitoring

Abstract The functional design of the smart electronic nose using polymer-film-coated quartz resonator gas sensors, based on the solubility parameter of sensing membrane and gases, is carried out in order to develop a sensor with excellent selectivity and high sensitivity for harmful gases such as toluene, acetaldehyde and ammonia gases. The polymer films such as propylene-butyl, polycarbonate and acrylic-resin of which the solubility parameter almost coincide with that of toluene, acetaldehyde and ammonia gases, respectively, are chosen as a sensing membrane material coated on the quartz resonator. It is found that propylene-butyl-film-coated quartz resonator gas sensor exhibits a high sensitivity and an excellent selectivity for toluene and p -xylene gas, as expected from a functional design based on solubility parameter. It is also found that polycarbonate-film-coated and acrylic-resin film-coated sensors exhibit high sensitivity and excellent selectivity for acetaldehyde and ammonia, respectively, also as expected. The results strongly suggest that solubility parameter is effective in the functional design of the sensing membrane of quartz resonator gas sensors. The successful identification of a specific gas is possible through the principal component pattern recognition analysis of the transient responses of each sensor for gases.

A smart gas sensor using polymer-film-coated quartz resonator microbalance

Abstract The copolymerized propylene–butyl, of which the “solubility parameter” almost coincides with that of harmful gases such as toluene, xylene, diethyether, chloroform and acetone, is chosen as a material of the sensing membrane coated on the quartz resonator. It is found that copolymerized propylene–butyl-film-coated quartz resonator microbalance gas sensor exhibits high sensitivity and excellent selectivity for these harmful gases, especially for toluene and xylene gas, suggesting that the “solubility parameter” is effective to the functional design of the sensing membrane of quartz resonator gas sensors.

TiOx film formation process by reactive sputtering

TiOx thin films were prepared by the sputtering of Ti atoms from a Ti target in a discharge gas including Ar and O2. O2 partial pressure during the sputtering was measured as a function of O2 gas flow rate introduced into the sputtering chamber. The pressure was found to increase linearly with the flow rate except for a region related with the sputtering mode change. In order to interpret the pressure change, a simple model for metal thin film formation was modified and applied. Fundamental relations expressing time change of the number density of Ti atoms and O2 molecules on a substrate surface were derived. Two‐dimensional (2D) motion of Ti atoms on the substrate was taken into account and 2D mean free path of those atoms was calculated. The collision frequency of Ti atoms with O2 molecules was then estimated and the rate of consumption (gettering) of O2 molecules was evaluated. It was found that the number density of Ti atoms on the substrate is one of the main factors determining the gettering effect....

Elastic and plastic energies in sputtered multilayered Ti-TiN films estimated by nanoindentation

Abstract Energetic parameters for describing mechanical properties, which makes it possible to discuss deformation behavior of a film elastically and plastically, are presented. Elastic energy and dissipated energy estimated from the area surrounded by a load–displacement curve obtained by nanoindentation measurement indicate the energy to deform a film elastically and plastically. The energy dissipated ratio defined as the ratio of dissipated energy to total applied energy to a film indicates the tendency for plastic deformation of a film. By considering the two energies and the energy dissipated ratio, deformation behavior of compositionally modulated Ti–TiN films with a multilayered structure was examined. At a modulation period of 10 nm, the reduction of the dissipated energy and the energy dissipated ratio were observed. Since the dissipated energy is consistent with energy for the propagation of the dislocations related to plastic deformation, it was assumed that the reduction was caused by a pinning effect for the propagation of the dislocations at interfaces of Ti and TiN.

Evaluation of adhesion strength of Ti films on Si(100) by the internal stress method

Abstract Titanium films were sputter deposited onto Si(100) surface. Adhesion strength of the Ti film was evaluated by the internal stress method. The Ti film was overcoated by a Ni coating in the state of a high internal stress, the value of which was about 0.5 GPa (tensile). The internal stress induces large normal and shear stress at the interface between the Ti film and the Si(100) surface. Those stresses increase with the increase of the Ni coating thickness. The stress distribution was evaluated by the finite element method. The evaluation shows that the normal stress on the interface is extremely large at the edge of the sample. This result suggests that a peeling of the Ti film is initiated at the edge and is consistent with observed spontaneous peeling phenomena. We could determine the adhesion strength of the Ti film by measuring the thickness of the Ni coating to peel off the Ti film. The value was found to range in 0.1–1 GPa region. The effect of the Ar ion bombardment of Si substrate on the adhesion enhancement was investigated in detail by this method.

Removal of Ion-Implanted Photoresists Using Atomic Hydrogen

In this paper, we investigated the removal characteristic of positive-tone novolak photoresists into which B, P, and As ions were implanted with doses of 5 × 10 12 -5 × 10 15 atoms/cm 2 at an acceleration energy of 70 keV using atomic hydrogen, and the hardening mechanisms for the photoresists. All of the ion-implanted photoresists with doses up to 5 × 10 15 atoms/cm 2 were removed without regard for ion species. The removal rates of the photoresists decreased with increasing ion-implantation dose due to hardening of the photoresist surfaces with implantation. The thickness of the surface-hardened layer of the photoresists decreased in the order of B → P → As, and the removal rate increased with decreasing thickness. The energy supplied from the ions to the photoresist concentrated on the surface side in the order of B → P → As, and the impact of the heavier ion on the photoresist was greater than that of the lighter ion. We deduced that the photoresists exhibited carbonization and cross-linkage attributable to the decrease in OH, CH, and 0 1s and the increase in C=C, C 1s, and π-conjugated systems.

Titanium carbide film deposition by DC magnetron reactive sputtering using a solid carbon source

Abstract Titanium carbide films with various C/Ti ratios have been deposited by DC magnetron sputtering using carbon sheets on the Ti target erosion area as a solid carbon source. By changing the number of carbon sheets (5 × 5 × 1 mm 3 ) from 0 to 24 pieces, the C/Ti compositional ratio of the films was changed. The composition, structure, and hardness of the deposited films were estimated as a function of the ratio of the source carbon area to the titanium target erosion area. The results of X-ray photoelectron spectroscopy showed that the C contents in the films increased to Ti: C = 60: 40 as the source C/Ti areal ratio increased. By X-ray diffraction, the films obtained for C/Ti areal ratios above 0.1 were found to possess the face-centered cubic structure and that the d -value of TiC (111) increased monotonically from 0.238 to 0.249 nm as the C/Ti areal ratio increased. The hardness of the films also increased monotonically as the C/Ti areal ratio increased, yielding a maximum of 11 GPa.

Photoresist Removal Using Atomic Hydrogen Generated by Hot-Wire Catalyzer and Effects on Si-Wafer Surface

We investigated an environmentally friendly method using atomic hydrogen generated by contact catalysis on a tungsten hot-wire catalyzer to remove photoresist instead of using chemicals and its effects on a Si-wafer surface. We eventually obtained a photoresist removal rate of 2.5 µm/min attributable to a reaction of atomic hydrogen with a positive-tone novolak photoresist, without thermal shrinkage of the photoresist film during atomic hydrogen irradiation because the photoresist shrank only under the influence of substrate heating by the catalyzer. The effects of atomic hydrogen irradiation on the substrate surfaces cannot be confirmed.

Hardness enhancement by compositionally modulated structure of Ti/TiN multilayer films

In this article results of an investigation into effects of multilayer structures of compositionally modulated Ti/TiN films on their hardness is presented. Compositionally modulated Ti/TiN multilayer films were deposited onto borosilicate glass substrates by a reactive gas flow rate modulation magnetron sputtering method using a combination of a Ti metal target and an Ar–N2 mixture discharge gas. In this method, a N2 gas flow rate was changed by a computer-controlled mass flow controller to produce films with a varying composition distribution. The film hardness was measured by nanoindentation. The film composition depth profiles were estimated by Auger electron spectroscopy and x-ray photoelectron spectroscopy. A TiN single layer film was also deposited to compare its hardness with those of the Ti/TiN multilayer films. Modulation periods examined in this study were 10, 15, 20, and 40 nm. It was found that the film with a modulation period of 20 nm showed a maximum hardness of 29 GPa and that the films wi...