Chuen-Lin Tien

Internal stress and optical properties of Nb2O5 thin films deposited by ion-beam sputtering.

The influence on the internal stress and optical properties of Nb2O5 thin films with ion-beam energy was investigated. Nb2O5 thin films were deposited on unheated glass substrates by means of ion-beam sputtering with different ion-beam voltage, Vb. The refractive index, extinction coefficient, and surface roughness were found to depend on the ion-beam energy. The stresses in thin films were measured by the phase-shifting interferometry technique. The film stress was also found to be related to Vb, and a high compressive stress of -0.467 GPa was measured at Vb = 850 V. The Nb2O5-SiO2 multilayer coatings had smaller average compressive stress as compared with single-layer Nb2O5 film.

An apparatus for the measurement of internal stress and thermal expansion coefficient of metal oxide films

A measuring apparatus based on a phase shifting interferometry technique to determine the mechanical properties of metal oxide films was presented. Thin films were prepared by ion-beam sputter deposition at low substrate temperature. Quantitative determination of the mechanical properties such as the internal stress, biaxial elastic modulus, and thermal expansion coefficient of metal oxide films were investigated. A phase shifting Twyman–Green interferometer with the phase reduction algorithm was setup to measure the temperature-dependent stress in thin films. Two types of circular glass plates, with known Young’s moduli, Poisson’s ratios, and thermal expansion coefficients, were used as coating substrate. The temperature-dependent stress behavior of the metal oxide films was obtained by heating samples in the range from room temperature to 70 °C. The stresses of thin films deposited on two different substrates were plotted against the stress measurement temperature, showing a linear dependence. Four oxid...

Simultaneous determination of the thermal expansion coefficient and the elastic modulus of Ta2O5 thin film using phase shifting interferometry

Abstract This paper reports on the application of a phase shifting interferometry technique for the concurrent measurement of the thermal expansion coefficient αf and the elastic modulus Ef /1 - Vf of Ta2O5 thin film. The Ta2O5 films were prepared by ion beam sputter deposition. The stresses in the thin films were measured with the phase shifting interferometry technique using two types of circular discs with known thermal expansion coefficients, Youngs moduli and Poissons ratios. The temperature-dependent stress behaviour of Ta2O5 films was obtained by heating samples in the range from room temperature to 70°C. The internal stresses of Ta2O5 thin films deposited on the BK-7 and Pyrex glass substrates were plotted against the stress measurement temperature, showing a linear dependence. From the slopes of the two lines in the stress versus temperature plot, the thermal expansion coefficient and the elastic modulus of Ta2O5 thin film are then calculated.

The measurement of thin film stress using phase shifting interferometry

Abstract A new technique for determining the stress of thin films is described. This technique combines digital phase shifting interferometry with image-processing software. A circular disc polished on one side is used as the coated substrate during film deposition. The average stress in thin films can be derived by comparing the deflection of the substrate before and after film deposition. The deflection of the substrate by the deposited film is obtained by the phase map. Using the Zernike polynomial fitting algorithm, a three-dimensional contour map is generated from the polynomial coefficients to visualize the deformation of the thin film and to examine the tensile or compressive stress after film deposition. Four oxide films prepared by ionbeam sputter deposition are investigated for their film stresses. The experimental results show that the stress values are concordant with measurements using other methods.

Magnetic Sensor Based on Side-Polished Fiber Bragg Grating Coated With Iron Film

This paper presents a novel fiber-optic magnetic sensor based on a side-polished fiber Bragg grating coated with thin iron film. The Bragg wavelength shift of 0.08 nm was measured at the distance of 0.38 mm between fiber sensor and Nd-Fe-B magnet with remanent flux density of 1.115 T. We demonstrate the ability to measure magnetic fields using such a device

High-sensitivity simultaneous pressure and temperature sensor using a superstructure fiber grating

In this paper, we show that both pressure and temperature can be measured simultaneously by using a high-sensitivity fiber sensor. This sensor has a superstructure fiber grating (SFG) encapsulated in a polymer-half-filled metal cylinder, which has two openings on opposite sides of the wall of the polymer, to sense the pressure. The sensed pressure is transferred into axial extended-strain. The variation of pressures and temperatures will cause the variation of the center-wavelength and reflection of the SFG simultaneously due to the optical response of the SFG composed by the fiber Bragg grating (FBG) as well as long-period grating (LPG). Thus, the sensor can be used for measuring pressure and temperature simultaneously. It has a pressure sensitivity of 3 times 10-2 MPa-1, better than that using only a bare FBG. Temperature sensitivities in both 0.02 nm per degC and 0.16 dBm per degC have experimentally been obtained. This fiber sensor can be applied for boiler as well as for the underwater depth measurement

Unraveling the Enhanced Electrical Conductivity of PEDOT:PSS Thin Films for ITO-Free Organic Photovoltaics

We present the structure and the optical and mechanical properties of highly conductive PEDOT:PSS (1:2.5 wt%, PH1000) thin films fabricated with and without an immersion treatment process using a solution containing 67% ethylene glycol and 33% hexafluoro-isopropyl alcohol, by volume. The enhanced electrical conductivity of the PEDOT:PSS thin films originated from the formation of a conducting PEDOT network in combination with an increased electron concentration due to the conformational changes in the PEDOT chains. The modified PEDOT:PSS thin film was used as a transparent anode electrode for P3HT:PCBM blended film-based photovoltaics, resulting in a power conversion efficiency of 3.28% under 1-sun illumination.

INTERFERENCE COATINGS BASED ON SYNTHESIZED SILICON NITRIDE

Silicon nitrides are synthesized by ion-assisted deposition with only one coating material and a nitrogen-ion-beam source. All the SiN(x) films are amorphous and mechanically strong. A wide range of refractive indices from 3.43 to 1.72 at a wavelength of 1550 nm is obtained. Near-IR antireflection coating and a bandpass filter based on the multilayers of SiN(x) and Si are demonstrated.

Thermal expansion coefficient and thermomechanical properties of SiN x thin films prepared by plasma-enhanced chemical vapor deposition

We present a new method based on fast Fourier transform (FFT) for evaluating the thermal expansion coefficient and thermomechanical properties of thin films. The silicon nitride thin films deposited on Corning glass and Si wafers were prepared by plasma-enhanced chemical vapor deposition in this study. The anisotropic residual stress and thermomechanical properties of silicon nitride thin films were studied. Residual stresses in thin films were measured by a modified Michelson interferometer associated with the FFT method under different heating temperatures. We found that the average residual-stress value increases when the temperature increases from room temperature to 100°C. Increased substrate temperature causes the residual stress in SiN(x) film deposited on Si wafers to be more compressive, but the residual stress in SiN(x) film on Corning glass becomes more tensile. The residual-stress versus substrate-temperature relation is a linear correlation after heating. A double substrate technique is used to determine the thermal expansion coefficients of the thin films. The experimental results show that the thermal expansion coefficient of the silicon nitride thin films is 3.27×10(-6)°C(-1). The biaxial modulus is 1125 GPa for SiN(x) film.

Measuring residual stress of anisotropic thin film by fast Fourier transform

A new method for the measurement of anisotropic stress in thin films based on 2-D fast Fourier transform (FFT) is presented. A modified Twyman-Green interferometer was used for surface topography measurement. A fringe normalization technique was also used to improve the phase extraction technique efficiently. The measurement of anisotropic stress in obliquely deposited MgF(2) thin film was demonstrated.