Jiro Sakata

Specimen size effect on tensile strength of surface-micromachined polycrystalline silicon thin films

A new tensile tester using an electrostatic-force grip was developed to evaluate the tensile strength and the reliability of thin-film materials. The tester was constructed in a scanning electron microscope (SEM) chamber for in situ observation and was applied for tensile testing of polycrystalline silicon (poly-Si) thin films with dimensions of 30-300 /spl mu/m long, 2-5 /spl mu/m wide, and 2 /spl mu/m thick. It was found that the mean tensile strengths of nondoped and P-doped poly-Si are 2.0-2.8 and 2.0-2.7 GPa, respectively, depending on the length of the specimens, irrespective of the specimen width. Statistical analysis of these size effects on the tensile strength predicted that the location of the fracture origin was on the edge of the specimen, which was Identified by the SEM observation of the fracture surface of the thin films.

Enhancement of giant magneto-impedance in layered film by insulator separation

Giant Magneto-Impedance (MI) effect of CoSiB/SiO/sub 2//Cu/SiO/sub 2//CoSiB films with line structures have been studied. Easy axes have been induced in perpendicular direction to the driving current, and the insulating SiO/sub 2/ layers have prevented the driving current from penetrating into the CoSiB layers. This structure has enabled the effective occurrence of resistance change at a frequency as low as several MHz. As a result, impedance change ratios /spl Delta/Z/Z/sub 0/=(Z/sub maximum/-Z(H/sub ext/=0))/Z(H/sub ext/=0) are much higher than that of any other layered film without insulating layers. The /spl Delta/Z/Z/sub 0/ at 20 MHz is as high as 700% at 11 Oe, and the maximum slope is 300%/Oe.

Tensile testing of insulating thin films; humidity effect on tensile strength of SiO2 films

Abstract Humidity effect on the strength of a plasma-enhanced chemical vapor deposition (CVD) SiO 2 film is evaluated with new tensile testing method using an electrostatic force grip. This method can test insulating films without troublesome specimen preparation and careful handling. To measure the humidity effect, two thin film tensile testers are used. One can perform test in air, and the other in a vacuum. With these apparatus, the tensile strength and the fracture toughness of the SiO 2 films are measured both in a vacuum and in air. The mean strength is 1.2–1.9 GPa in a vacuum and 0.6–1.0 GPa in air, and the mean toughness is 1.3–2.0 MPa √m in a vacuum and 0.6–0.9 MPa √m in air. These values are strongly affected by the testing environment, and these effects must be mainly due to water in air.

Specimen size effect on tensile strength of surface micromachined polycrystalline silicon thin films

A new tensile tester using electrostatic force grip was developed to evaluate the tensile strength and the reliability of thin film materials. The tester was constructed in a SEM chamber for in-situ observation, and was applied for tensile testing of polycrystalline silicon (poly-Si) thin films with dimensions of 30-300 /spl mu/m long, 2-5 /spl mu/m wide and 2 /spl mu/m thick. It was found that the mean tensile strength is 2.0-2.7 GPa depending on the length of the specimens, irrespective of the specimen width. Statistical analysis of these size effects on the tensile strength predicted that the location of the fracture origin is on the edge of the specimen, which is identified by the SEM observation of the fracture surface of the thin films.

Preparation of organic thin films by an electrospray technique I. Crystal forms and their orientation in poly(vinylidene flouride) films

Abstract The utilization of ions has proved effective for preparing highly oriented films. In this paper, a new electrospray technique (ESP) is discussed. Poly(vinylidene fluoride) (PVDF) solution (0.2 wt.% in dimethylformamide) was passed through a nozzle to which a high voltage (8–15 kV) was applied, and sprayed into dry nitrogen gas. The nitrogen gas was made to flow in order to evaporate the solvent. Charged droplets of the solute were transported to a conductive substrate which was grounded. Then the PVDF film was formed on the substrate. The results of X-ray diffraction and IR measurements indicated that the PVDF films consisted chiefly of form I crystal. From the results of IR dichroic measurements by IR reflection absorption spectroscopy methods with polarized light, it was found that the form I crystal was oriented; molecular chain axes were parallel to the substrate surface, and the CF 2 dipole was perpendicular to the surface and parallel to the applied field. Films possessing pyroelectricity could be obtained, and the largest pyroelectric coefficient was 4.0 nC cm −2 K −1 which was larger than that of conventional PVDF pyroelectric films.

ORGANIC/INORGANIC SUPERLATTICES WITH ORDERED ORGANIC LAYERS

Superlattices consisting of alternating layers of organic and inorganic materials have been fabricated from 3,4,9,10‐perylenetetracarboxylic diimide (PTCDI), copper phthalocyanine (CuPc), and MgF2 by molecular‐beam deposition. From the small‐angle x‐ray diffraction patterns of PTCDI/MgF2 and CuPc/MgF2 superlattices, a periodically layered structure is confirmed through the entire stack. The PTCDI layers in the PTCDI/MgF2 superlattices have a high degree of structural ordering, in which molecular planes are nearly parallel to the substrate surface. On the other hand, the CuPc/MgF2 superlattices have a poorly ordered structure in the CuPc layers. It is found that the optical absorption spectra of these superlattices are different from those of organic single films and significantly change with varying organic layer thickness. Such spectral changes can be interpreted by the effect of the aggregate size and the coexistence of two different crystal forms.

Tensile Strength and Fracture Toughness of Surface Micromachined Polycrystalline Silicon Thin Films Prepared Under Various Conditions

A new tensile tester for thin films was developed to evaluate the reliability of the microelectro-mechanical devices. This tester uses the grip that fixes a thin film specimen to a probe by electrostatic force. The authors applied this tester for polycrystalline silicon (poly-Si) thin-films prepared under various conditions. The microstructure of the film is controlled by the crystallizing temperature. The process conditions and the microstructures that contribute to the strength of poly-Si film are identified by the tensile strength and the fracture toughness. The mean tensile strength of each specimen size ranges from 1.8 to 3.7 GPa, and the fracture toughness calculated from the strength of the notched specimen ranges from 1.9 to 4.5 MN/m{sup 3/2}. The 1000 C annealed film has higher strength and toughness than the other films because of the high annealing temperature and the small grain size. The contributions to the strength are evaluated by the additional annealing at 1000 C for the low temperature annealed films.

The molecular orientation in copper phthalocyanine thin films deposited on metal film surfaces

Abstract The molecular orientation in copper phthalocyanine (CuPc) films deposited on metal films of Au, Ag, Cu and Cr has been studied by reflection-absorption infrared spectroscopy and X-ray diffraction. The molecular planes of CuPc in the ultra-thin films (corresponding to several tens of monolayers) deposited on Au, Ag and Cu films were found to be nearly parallel to the metal film surfaces. Further deposition (up to 100 nm) on such thin films produces a molecular orientation with the molecular planes inclined away from the metal film surfaces. This corresponds to a crystal structure of the α phase with a standing b axis configuration. However, the molecular planes of the CuPc deposited on Cr films are rather perpendicular to the Cr film surfaces. These CuPc films are in the α phase with a parallel b axis configuration.

Structures and optical properties of organic/inorganic superlattices

A new class of superlattice materials consisting of alternating layers of organic and inorganic materials has been prepared from 8‐hydroxyquinoline aluminum (Alq) and MgF2 by vacuum deposition. The Alq layer thickness in the superlattices was varied from 10 to 50 A. Small‐angle x‐ray diffraction measurements indicate that the superlattices have very uniform layered structure throughout the entire stack, and the interfacial roughness is much smaller than 10 A. From the optical absorption and photoluminescence measurements, it is found that the exciton energy shifts to higher energy with decreasing Alq layer thickness. The changes of the exciton energy could be interpreted as the confinement effects of exciton in the Alq thin layers.

Vibrating gyroscope consisting of three layers of polysilicon thin films

Abstract A vibrating gyroscope consisting of three layers of polysilicon thin films has been developed. It has an upper electrode over a resonating mass for detecting accurately the sensing vibration oscillated by the Coriolis force . The resonant frequencies of both the driving and sensing vibrations are controlled by the DC bias to comb electrodes that are used for detecting the driving vibration. The offset on the angular rate output due to the mechanical and electromechanical couplings is decreased by an unbalanced differential oscillation. With this tuning method and the offset reduction, the angular rate was detected. The resolution of 1° s −1 is achieved.