Qijing Lin

Range Analysis of Thermal Stress and Optimal Design for Tungsten-Rhenium Thin Film Thermocouples Based on Ceramic Substrates

A thermal stress range analysis of tungsten-rhenium thin film thermocouples based on ceramic substrates is presented to analyze the falling off and breakage problems caused by the mismatch of the thermal stresses in thin film thermocouples (TFTCs) and substrate, and nano-indentation experiments are done to measure and calculate the film stress to compare with the simulation results. Optimal design and fabrication of tungsten-rhenium TFTCs based on ceramic substrates is reported. Static high temperature tests are carried out, which show the optimization design can effectively reduce the damage caused by the thermal stress mismatch.

Multiferroic heterostructures of Fe3O4/PMN-PT prepared by atomic layer deposition for enhanced interfacial magnetoelectric couplings

In this work, multiferroic heterostructures have been prepared by in situ growing oxide magnetic films on ferroelectric single crystal substrates using atomic layer deposition (ALD). Strong interfacial mechanical coupling between the magnetic and ferroelectric phases has been created, arising from the formation of chemical bonds at the interface due to the nature of layer-by-layer self-limiting growth mechanism of the ALD technique. An enhanced magnetoelectric (ME) coupling has been achieved, which allows an electric field to robustly switch magnetic anisotropy up to 780 Oe. In addition, electrical impulse non-volatile tuning of magnetism has also been realized through partially coupled ferroelectric/ferroelastic domain switching. The ALD growth of magnetic oxide films onto ferroelectric substrates provides an effective platform for the preparation of multiferroic heterostructures at low temperatures with an improved ME coupling, demonstrating a great potential for applications in 3D spintronics, microele...

Agglomeration and dendritic growth of Cu/Ti/Si thin film

Agglomeration and the transformation from random fractal to dendritic growth have been observed during Cu/Ti/Si thin film annealing. The experimental results show that the annealing temperature, film thickness, and substrate thickness influenced the agglomeration and dendritic growth. Multifractal spectrum is used to characterize the surface morphology quantificationally. The shapes of the multifractal spectra are hook-like to the left. Value of Δα increases with the annealing temperature rising, and Δf increases from 500°C to 700°C but reduces from 700°C to 800°C. The dendritic patterns with symmetrical branches are generated in the surfaces when the thin films were annealed at 800°C.

Modeling and Analysis of a Combined Stress-Vibration Fiber Bragg Grating Sensor

A combined stress-vibration sensor was developed to measure stress and vibration simultaneously based on fiber Bragg grating (FBG) technology. The sensor is composed of two FBGs and a stainless steel plate with a special design. The two FBGs sense vibration and stress and the sensor can realize temperature compensation by itself. The stainless steel plate can significantly increase sensitivity of vibration measurement. Theoretical analysis and Finite Element Method (FEM) were used to analyze the sensor’s working mechanism. As demonstrated with analysis, the obtained sensor has working range of 0–6000 Hz for vibration sensing and 0–100 MPa for stress sensing, respectively. The corresponding sensitivity for vibration is 0.46 pm/g and the resulted stress sensitivity is 5.94 pm/MPa, while the nonlinearity error for vibration and stress measurement is 0.77% and 1.02%, respectively. Compared to general FBGs, the vibration sensitivity of this sensor is 26.2 times higher. Therefore, the developed sensor can be used to concurrently detect vibration and stress. As this sensor has height of 1 mm and weight of 1.15 g, it is beneficial for minimization and integration.

Buckling and Delamination of Ti/Cu/Si Thin Film During Annealing

In this paper, the formation of buckling and delamination of sandwiched stacking of Ti/Cu/Si thin film are investigated. The crystallization structures, the composition of the Cu/Ti thin films, and the surface morphology are measured during annealing. The results show that the solid-phase reaction between Cu and Ti occurs at the interface. Buckling is initiated in the thin film annealed at 600°C. The volume expansion promotes the buckling and further produces microcracks. With increasing volume expansion, there are cavities formed in the middle layer when the annealing temperature is up to 700°C. Finally, thin film is delaminated from the substrate.

Surface characterization of Cu/Ti thin films by fractal analysis

Copper/Titanium (Cu/Ti) metallic thin bilayer films, xCu/10nmTi/Si and xCu/30nmTi/Si (x=10nm, 20nm, 30nm, respectively), were deposited by DC magnetron sputtering technique. An atomic force microscopy (AFM) was used to measure the surface morphology. The height-height correlation function, described by the surface parameter of roughness exponent α, together with the evolutions of the familiar parameters of roughness w and autocorrelation length ξ, was used to describe the surface quantitatively. The fractal dimension Df of the surface was calculated. The values of Df reduce with the Cu film thickness increasing for the samples of Cu/10nmTi/Si and increase for the samples of Cu/30nmTi/Si. The surface will be rougher for the samples of Cu/10nmTi/Si as the Cu film increasing from 10nm to 30nm and become smoother for the samples of Cu/10nmTi/Si.

High Temperature High Sensitivity Multipoint Sensing System Based on Three Cascade Mach–Zehnder Interferometers

A temperature multipoint sensing system based on three cascade Mach–Zehnder interferometers (MZIs) is introduced. The MZIs with different lengths are fabricated based on waist-enlarged fiber bitapers. The fast Fourier transformation is applied to the overlapping transmission spectrum and the corresponding interference spectra can be obtained via the cascaded frequency spectrum based on the inverse Fourier transformation. By analyzing the drift of interference spectra, the temperature response sensitivities of 0.063 nm/°C, 0.071 nm/°C, and 0.059 nm/°C in different furnaces can be detected from room temperature up to 1000 °C, and the temperature response at different regions can be measured through the sensitivity matrix equation. These results demonstrate feasibility of multipoint measurement, which also support that the temperature sensing system provides new solution to the MZI cascade problem.

Measurement study of residual stress on tungsten-rhenium thin film thermocouples by nanoindentation technology

In this paper, Nano-indentation technology is used to test the mechanical property of the tungsten-rhenium thin film, including hardness, elastic modulus and residual stress. The effects of different heat treatment temperature and different substrates on the hardness and elastic modulus of tungsten-rhenium films were studied. We research three substrates which are silicon carbide ceramic, aluminum oxide ceramic and zirconium oxide ceramic. Test results show that the tungsten-rhenium films on aluminum oxide ceramic shows the biggest values of elastic modulus and the smallest on silicon carbide ceramic. However, value of hardness is biggest on zirconium oxide ceramic and smallest on aluminum oxide ceramic. Besides, the heat treatment temperature has high influence on hardness and elastic modulus of tungsten-rhenium film. And under different substrates, the hardness and elastic modulus of film on zirconium oxide ceramic is the most sensitive to heat treatment temperature. By contrast, silicon carbide ceramic is the least.

A protected tungsten-rhenium thin film thermocouples sensor

A tungsten-rhenium thin film thermocouples is designed and fabricated, and the characteristics of thin film thermocouples in different temperatures are investigated via numerical analysis and analog simulation. Protective film was presented to prevent from the oxidation and evaporation of tungsten-rhenium TFTCs at high temperature. The experiment shows TFTCs sensor with protective film have an acceptable linearity up to 1370K with a suitable voltage output and can work for half an hour at 1370K, however the TFTCs without protective films break after high temperature constant at 900K.

A Fabry-Perot interferometer for high temperature measurement based on mode analysis

A fourier analysis applied to the Fabry-Perot interferometer(FPI) transmission spectrum for temperature measurement is proposed and experimentally demonstrated in this paper. In the fast Fourier transform (FFT) spectrum of the FPI transmission spectrum, a higher order model is separated from the transmission spectrum and the spatial frequency spectra of the higher order model is detected. As the temperature change, the shifts of the spatial frequency spectrum will be observed. The sensitivity of the temperature is 0.00012/(nm · °C). The proposed sensor features the advantages of easy fabrication, compact structure and stable chemical property, and it exhibits great potential in high temperature measurement.