Cathodoluminescence Spectroscopic Stress Analysis for Silicon Oxide Film and Its Damage Evaluation.

We describe the stress analysis of silicon oxide (SiO2) thin film using cathodoluminescence (CL) spectroscopy and discuss its availability in this paper. To directly measure the CL spectra of the film under uniaxial tensile stresses, specially developed uniaxial tensile test equipment is used in a scanning electron microscope (SEM) equipped with a CL system. As tensile stress increases, the peak position and intensity proportionally increase. This indicates that CL spectroscopy is available as a stress measurement tool for SiO2 film. However, the electron beam (EB) irradiation time influences the intensity and full width at half maximum (FWHM), which implies that some damage originating from EB irradiation accumulates in the film. The analyses using Raman spectroscopy and transmission electron microscopy (TEM) demonstrate that EB irradiation for stress measurement with CL induces the formation of silicon (Si) nanocrystals into SiO2 film, indicating that CL stress analysis of the film is not nondestructive, but destructive inspection.

Temperature Dependence on Tensile Mechanical Properties of Sintered Silver Film.

This paper investigates the influence of temperature on tensile mechanical properties of sintered silver (s-Ag) films with 8-10 µm in thickness for fundamental reliability design of semiconductor systems. The s-Ag film sintered under a pressure of 60 MPa possesses the porosity (p) around 5% determined from cross-sectional scanning electron microscope (SEM) images. The stress-strain (S-S) curves of s-Ag and pure silver (p-Ag) films are obtained using originally designed uniaxial tensile tester at temperatures from 25 °C to 150 °C. The S-S curves of p-Ag indicate ductile behavior irrespective of temperature, whereas those of s-Ag indicate brittle-ductile transition at 120 °C. Compared with p-Ag, s-Ag possesses low Young's modulus (E) and high ultimate tensile strength (UTS) below 80 °C. The mechanism of brittle-ductile transition is discussed based on fracture surface observation results.

Strength of carbon nanotubes depends on their chemical structures.

Single-walled carbon nanotubes theoretically possess ultimate intrinsic tensile strengths in the 100-200 GPa range, among the highest in existing materials. However, all of the experimentally reported values are considerably lower and exhibit a considerable degree of scatter, with the lack of structural information inhibiting constraints on their associated mechanisms. Here, we report the first experimental measurements of the ultimate tensile strengths of individual structure-defined, single-walled carbon nanotubes. The strength depends on the chiral structure of the nanotube, with small-diameter, near-armchair nanotubes exhibiting the highest tensile strengths. This observed structural dependence is comprehensively understood via the intrinsic structure-dependent inter-atomic stress, with its concentration at structural defects inevitably existing in real nanotubes. These findings highlight the target nanotube structures that should be synthesized when attempting to fabricate the strongest materials.

Charge screening strategy for domain pattern control in nano-scale ferroelectric systems.

Strain engineering is a widespread strategy used to enhance performance of devices based on semiconductor thin films. In ferroelectrics strain engineering is used to control the domain pattern: When an epitaxial film is biaxially compressed, e.g. due to lattice mismatch with the substrate, the film displays out-of-plane, often strongly enhanced polarization, while stretching the film on the substrate results in in-plane polarization. However, this strategy is of a limited applicability in nanorods because of the small rod/substrate contact area. Here we demonstrate another strategy, in which the polar axis direction is controlled by charge screening. When charge screening is maintained by bottom and top metallization, the nanorods display an almost pure c-domain configuration (polarization perpendicular to the substrate); when the sidewalls of the nanorods are metallized too, a-domain formation prevails (polarization parallel to the substrate). Simulations of the depolarization fields under various boundary conditions support the experimental observations. The employed approach can be expanded to other low-dimensional nano-scale ferroelectric systems.

Piezoresistive effect in p-type 3C-SiC at high temperatures characterized using Joule heating.

Cubic silicon carbide is a promising material for Micro Electro Mechanical Systems (MEMS) applications in harsh environ-ments and bioapplications thanks to its large band gap, chemical inertness, excellent corrosion tolerance and capability of growth on a Si substrate. This paper reports the piezoresistive effect of p-type single crystalline 3C-SiC characterized at high temperatures, using an in situ measurement method. The experimental results show that the highly doped p-type 3C-SiC possesses a relatively stable gauge factor of approximately 25 to 28 at temperatures varying from 300 K to 573 K. The in situ method proposed in this study also demonstrated that, the combination of the piezoresistive and thermoresistive effects can increase the gauge factor of p-type 3C-SiC to approximately 20% at 573 K. The increase in gauge factor based on the combination of these phenomena could enhance the sensitivity of SiC based MEMS mechanical sensors.

Fabrication of Tetragonal Pb(Zr,Ti)O3 Nanorods by Focused Ion Beam and Characterization of the Domain Structure.

It has been widely revealed and discussed that the properties of ferroelectric nanostructures vary with their dimensionality and size. The mechanical substrate clamping and the depolarization field are considered as major factors, which cause their unique properties. In this paper, we fabricated tetragonal {100}-Pb(Zr, Ti)O3 rods with 100 nm - 4 µm widths on Nb-doped SrTiO3 substrates by using focused ion beam, and characterized their domain structure by synchrotron micro X-ray diffraction. It was found that the clapping angle in the a/c-domain structure became larger with decreasing the rod width, which indicates the significant reduction of substrate clamping by fabricating narrow rods.

Tensile elongation measurement device with in-plane bimorph actuation mechanism.

This paper describes the development of a bimorph-actuated twin-probe device utilized for uniaxial tensile test to measure tensile elongation of a film specimen. The device consists of two sets of microscale cantilever probes with piezoresistive sensor to detect the position of two gauge marks on a specimen, and multiple pairs of bimorph actuators to produce in-plane motion for scanning those marks. By Joule's heating, the bimorph actuators connecting two cantilever probes are able to move along the tensile direction. When those probes climb the gauge marks having convex line structure, the sensor signals originating from the piezoresistive effect are output by the cantilever's deflection. The elongation of a tensile specimen can be calculated from the moving velocity of cantilever probes and the time difference between two sensor signals. The performance of the device produced through conventional micromachining technologies was investigated. Elongation of single-crystal silicon (SCS) film specimen was measured during uniaxial tensile loading. The mean Young's modulus of 165.1 GPa which was measured by using the device was in good agreement with the analytical value. The proposed bimorph-actuated twin-probe device would be useful for measuring elongation of a film specimen during the tensile test.

In-situ cathodoluminescence spectroscopy of silicon oxide thin film under uniaxial tensile loading.

In this paper, in-situ cathodoluminescence (CL) stress analysis of a silicon oxide (SiO(x)) thin film prepared by wet thermal oxidation is described. The specially-developed uniaxial tensile loading jig was used to apply tensile displacement to the SiO(x) film specimen. CL spectra of the specimen during tensile loading were obtained, and the peak position of around 1.85 eV emission band was monitored for tensile stress analysis. The peak position gradually shifted towards higher/lower energy side when tensile displacement increased/decreased. The tensile stress-to-emission energy ratio of 6.21-8.97 x 10(2) GPa/eV was estimated on the basis of linear elastic theory, which demonstrated that CL is able to provide information on stress induced in the film. Scanning electron microscopy (SEM) revealed that the fracture of SiO(x) and SCS laminated structure occurred at the vicinity of SiO(x) film surface.

Mechanical property measurements of nanoscale structures using an atomic force microscope.

This paper describes nanometer-scale bending tests of fixed single-crystal silicon (Si) and silicon dioxide (SiO2) nanobeams using an atomic force microscope (AFM). The technique is used to evaluate elastic modulus of the beam materials and bending strength of the beams. Nanometer-scale Si beams with widths ranging from 200 to 800 nm were fabricated on a Si diaphragm using field-enhanced anodization using an AFM followed by anisotropic wet etching. Subsequent thermal oxidation of Si beams was carried out to create SiO2 beams. Results from the bending tests indicate that elastic modulus values are comparable to bulk values. However, the bending strength appears to be higher for these nanoscale structures than for large-scale specimens. Observations of the fracture surface and calculations of the crack length from Griffith's theory appear to indicate that the maximum peak-to-valley distance on the beam top surfaces influence the values of the observed bending strengths.