Tse Chang Li

Fatigue Life Study of ITO/PET Specimens in Terms of Electrical Resistance and Stress/Strain Via Cyclic Bending Tests

Bending tester in reciprocating motion is adopted to study the fatigue resistance and fatigue life of indium tin oxide (ITO) films deposited on poly(ethylene terephthalate) (PET) substrate with various prestrain levels. A commercial micro-compression tester and ANSYS-Workbench software are used to determine the stress versus strain curves, and thus the strain energy of a fixed volume in the specimen. A bending tester without a cycle limitation is designed to carry out ITO-film fatigue life tests. Two points symmetric with respect to the specimens central line are set to measure the films electrical resistance variation with the number of cycles in reciprocating motion. The number of cycles in the bending tests corresponding to the fatigue life of ITO film is determined on the bases of both the strain at which 63% of the material fails and the electrical resistance which has 10% rise w.r.t. the initial one before bending test. The mean electrical resistance increases with increasing number of cycles and prestrain applied to the PET substrate. Of the four substrate prestrains tested (0%, 2%, 4%, and 6%), the change in electrical resistance between the beginning and end of the test was highest for the PET-6%/ITO specimen regardless of the maximum acceleration of the tester. With the same substrates prestrain and at the same maximum acceleration, the number of cycles for fatigue life predicted by these two models are fairly close. Increasing either the substrate prestrain or the jigs acceleration decreases the alternating stress and increases the strain during reciprocating motion, lowering the fatigue life of the film. The strain energy defined for a fixed volume in the specimen is found always asymptotic to a constant value. The number of cycles corresponding to the beginning of this constant strain energy is found close to those of fatigue cycles predicted by the models mentioned above. The strain energy method is thus provided as an effective way to predict the fatigue life of the specimens without fatigue limit in the curve.

Effects of Prestrain Applied to a Polyethylene Terephthalate Substrate Before the Coating of Al-Doped ZnO Film on Film Quality, Electrical Properties, and Pop-In Behavior During Nanoindentation

Four kinds of polyethylene-terephthalate (PET)/Al-doped zinc oxide (AZO) specimen are prepared to examine the effects of prestrain applied to the PET substrate before the coating of the AZO film on the mechanical, material, and electrical properties, and the start of pop-in in the loading phase of nanoindentation. The electrical contact resistance function is used to measure the variations of electrical current during the nanoindentation process. With the aid of the stress-strain profile, the inflection point of the load-depth profile in the loading phase is identified as the start of pop-in, at or nearby which the electrical current sharply increases due to the significant increase in the indenter-film contact area. The pop-in depth decreases with increasing prestrain. The behavior demonstrated in the pop-in depth due to the change in the prestrain is exactly opposite to those of the quantity and the mean size of submicrometer voids/cracks. Increase in the quantity/size of film voids/cracks generally reduces the specimens carrier mobility. The carrier mobility is presented to be inversely proportional to the sheet resistance. The electrical current created at the end of the loading process has its value inversely proportional to the number/size of film voids/cracks.

Effects of sputtering-deposition inclination angle on the IGZO film microstructures, optical properties and photoluminescence

Abstract: IGZO/PET specimens were respectively prepared with 0°, 15°, 30°, 45°, and 60° as the inclination angle of the thin film deposition. The n-type conductivity was identified in these specimens. The following parameters, including the film thickness and morphologies of the top and lateral surfaces, the mechanical properties, chemical compounds and their primary lattices in X-ray diffraction (XRD) patterns, and the X-ray photoelectron spectrometries (XPS) for Ga2p, Ga3d, In3d, Zn2p, and O1s are presented. IR is defined as the intensity ratio of the InGaO3(ZnO)3 peak value to the sum of the peak values of InGaO3(ZnO)3 and InGaZnO4. Decompositions of the O1s and Ga3d spectra provide nearly Gaussian profiles of Ga-Ga, In4d, Ga-O, O1, O2, and O3. The O2 intensity ratio IRO2, which is defined as the ratio of O2 peak intensity to the peak intensity sum of O1 and O2, was evaluated for these five specimens. Depth profiles of the distributions of O, Zn, Ga, and In ions were obtained by secondary ion mass spectrometry (SIMS), and the slope (Go) of the O-ion profile in the decaying region was obtained as a function of inclination angle. Increases in the inclination angle can effectively reduce surface roughness. The peak intensities of Ga2p, Ga3d, In3d, Zn2p, and O1s formed in the specimen preparations with a nonzero inclination angle were always lower than those of the IGZO_0° specimen. Although an increase in inclination angle can raise the IRO2 value, a nonzero inclination angle yielded an IR value lower than that of the IGZO_0° specimen. Moreover, the IRO2 value increased with (negative) Go decrease as the response. The combined result of increasing IRO2 and the In-O and Ga-O bonds, and decreasing the IGZO film thickness can increase light transmission. Specimens with a larger surface roughness result in a higher reflection. The IR parameter for the specimens with a nonzero inclination angle has a value smaller than that of the IGZO_0° specimen; as such, an increase in IR is advantageous for increasing the n-type conductivity. The decreasing rate of extinction coefficient k with respect to wavelength in the visible light region increases significantly with increasing IRO2. IR and IRO2 are therefore the governing factors of the peak intensities for the three decomposed profiles of micro-photoluminescence (PL). Increasing IR and IRO2 or decreasing film thickness is advantageous for increasing the PL peak intensities. Increases in the product values of IR and IRO2 are favorable for increasing the peak intensities of violet and ultraviolet.

Effects of graphene layers in IGZO / graphitelike +Ni/SiO2/Si wafer specimens on electrical and optical properties in tribotests

In the present study, graphite-like +Ni/SiO2/Si wafer specimens were prepared using a co-sputtering system. Then, indium gallium zinc oxide (IGZO) films were deposited onto the graphite-like +Ni/SiO2/Si wafer specimens at deposition powers of 60, 80, and 100 W, respectively. The effects of IGZO deposition power on the specimen’s microstructure and the vacancy defects in the graphite-like +Ni layer are evaluated in terms of the electrical and mechanical properties of the as-prepared specimens. The effects of the graphite-like +Ni film on the electrical resistance of the IGZO film with microcracks is evaluated using a tribotester. The quantity and mean size of microcracks and variations of electrical resistance of the IGZO/graphite-like +Ni/SiO2/Si wafer specimens with time are used to evaluate the role of the graphite-like +Ni layer as an alternate conductor of electric current when the IGZO film is degraded by microcracks. The growth of hillocks in the graphite-like +Ni layer can be enhanced by increasing the IGZO deposition power. These hillocks cause the graphite-like +Ni layer to be convex and have an uneven film thickness, and lead to vacancy defects in the graphite-like film. The O atoms of IGZO were incorporated into graphene in the graphite-like layer as substitutional impurities. The effects of these impurities on the electrical structure with a characteristic of superconductors occur intermittently in the tribotests, resulting in a sharp reduction in the electrical resistance of a specimen. An increase in the intensity ratio, IRO2, related to oxygen vacancies, increases the peak intensities (PIs) of elemental Ga and the Ga-O bond, and decreases that of the Ga-Ga bond. In the IGZO/Glass specimens, a small reduction of the average transmittance is created in the specimens prepared by increasing the deposition power from 60 W to 100 W. The behavior of reflection is exactly opposite to that of transmittance. An increase in deposition power is favorable for the rise of optical band gap (Eg). Increasing the concentration of Zn2p3/2 or Zn2p1/2 increases PIGreen in photoluminescence profiles. Reductions in either In atoms or C-C and C-O bonds increase PIOrange. PIRed and can be increased by either increasing PIGa-Ga or decreasing the values of PIGa2p3/2, PIGa2p1/2, and PIGa-O.

Effects of inclination angle during Al-doped ZnO film deposition and number of bending cycles on electrical, piezoelectric, optical, and mechanical properties and fatigue life

A flat plate with an adjustable inclination angle between the ion beam and the direction normal to a polyethylene terephthalate (PET) substrate is designed for a deposition stage. Five inclination angles are used to prepare PET/aluminum-doped zinc oxide specimens in order to examine the effects of inclination angle and number of bending cycles on several parameters. The O2 peak intensity ratio ( IRO2), obtained from x-ray photoelectron spectroscopy, is identified as one of the controlling factors of the electrical, optical, piezoelectric, and mechanical properties. The effect of inclination angle on IRO2 and the effects of IRO2 on the peak intensity ratios, IRZnO (002) and IRZnO (103), obtained from x-ray diffraction analyses, the composite grain size, and the residual stress in the thin film are investigated systematically. An increase in the inclination angle increases the peak intensity ratios of IRO2 and IRAl2O3, and reduces that of IRZnO. An increase in IRO2 decreases the volume fraction of IRZnO (00...

Tribology Properties of IGZO Films by the Sliding Contacts of Reciprocating Motion

In the present study, sliding tribo tests with reciprocating motion were carried out to simulate the thumb-driven wear arising in indium gallium zinc oxide (IGZO) specimens prepared at five inclination angles during film deposition. Frictional and normal forces, Fx and Fy, and vibrations were used to analyze energy dissipation (ΔW) and composite mean force fluctuation intensities (IFSS). Friction coefficient is lowered by decreasing the mean surface roughness (Ra); its increase can raise ΔW. The friction coefficients of samples prepared with a nonzero inclination angle were lower than that of the IGZO_0° specimen.

Effects of Sputtering Power on Optical and Electrical Properties of Al-Doped ZnO Thin Film on Flexible Substrates

AZO thin films were deposited using a magnetron sputtering system with an AZO target (with 3wt% Al2O3) on polyethylene terephthalate (PET) substrates with pre-strain. The effect of sputtering power on the optical and electrical properties of AZO films was investigated. For samples deposited on pre-strained PET substrates, X-ray diffraction was used to determine the c-axis orientation of AZO films deposited at 60, 80, and 100 W. Results show that resistivity decreased with increasing sputtering power, which might result from the better crystalline structure and fewer grain boundaries obtained at high power. The transmittance increased when the power was increased from 60 to 100 W. The absorption edge thus decreased for AZO film deposited at 100 W.