Hui Min Xie

Fabrication of high-frequency moire gratings for microscopic deformation measurement using focused ion beam milling

In this paper, the fabrication technique of high-frequency moire gratings with a focused ion beam (FIB) is studied thoroughly and comprehensively. The concept is proposed for the first time that the frequency and the size of the grating must be designed to meet the requirements of measurement accuracy and the view field at the same time. Some skills are summarized to get high quality gratings. To check its ability for high temperature use, a grating with a frequency of 2000 lines mm−1 is fabricated on the amorphous SiC micro-beam. SEM moire are recorded at room temperature and after high temperature of 350 °C and 550 °C respectively. The fringes are distinct at all stages except for a contrast degradation after high temperature, which demonstrates that SEM moire combined with the grating fabricated by FIB milling is a promising tool to measure microscopic deformation of micro-device at room temperature and high temperature.

The digital geometric phase technique applied to the deformation evaluation of MEMS devices

Quantitative evaluation of the structure deformation of microfabricated electromechanical systems is of importance for the design and functional control of microsystems. In this investigation, a novel digital geometric phase technique was developed to meet the deformation evaluation requirement of microelectromechanical systems (MEMS). The technique is performed on the basis of regular artificial lattices, instead of a natural atom lattice. The regular artificial lattices with a pitch ranging from micrometer to nanometer will be directly fabricated on the measured surface of MEMS devices by using a focused ion beam (FIB). Phase information can be obtained from the Bragg filtered images after fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) of the scanning electronic microscope (SEM) images. Then the in-plane displacement field and the local strain field related to the phase information will be evaluated. The obtained results show that the technique can be well applied to deformation measurement with nanometer sensitivity and stiction force estimation of a MEMS device.

The artificial periodic lattice phase analysis method applied to deformation evaluation of TiNi shape memory alloy in micro scale

The basic principle of the artificial periodic lattice phase analysis method on the basis of an artificial periodic lattice was thoroughly introduced in this investigation. The improved technique is intended to expand from nanoscale to micro- and macroscopic realms on the test field of experimental mechanics in combination with a submicron grid, which is produced by a focused ion beam (FIB). Phase information can be obtained from the filtered images after fast Fourier transform (FFT) and inverse FFT. Thus, the in-plane displacement fields as well as the local strain distributions related to the phase information will be evaluated. The application scope of the technique was obtained by the simulation experiment. The displacement fields as well as strain distributions of porous TiNi shape memory alloy were calculated by the technique after compressive loading in micro scale. The specimen grid was directly fabricated on the tested flat surface by employing a FIB. The evolution rule of shear zones in micro area near porous has been discovered. The obtained results indicate that the technique not only could be well applied to measuring full field deformation, but also, more significantly, is available to present mechanical properties in micro scale.

Investigation on the Deformation of TiNi Shape Memory Alloy with a Crack Using Moiré Interferometry

Martensitic phase transformation can greatly affect the mechanical behaviors and the stress-strain response of shape memory alloys (SMAs). In this study, the effect of martensitic phase transformation on the deformation of a single-crystal TiNi SMA specimen with a triangle crack was investigated experimentally by means of moiré interferometry method. A typical displacement field and the corresponding strain field in areas both around and far from the tip of the crack were measured in a certain time during the loading process in which the tensile load is coupled with the stress-induced martensitic phase transformation. Some characteristics of the deformation and the martensitic phase transformation of the specimen are revealed. These results may provide a reliable support for revealing the fracture mechanism of single crystal TiNi SMAs, and may enable further development in putting forward the failure criterion of SMAs.

An Experimental Study on Creep Deformation of PBX with Laser Moiré Interferometry Method

In this paper, the creep deformation of PBX was measured using the moiré interferometry. The experimental results show a different creep process compared with pure high polymer and this phenomenon is preliminary analyzed from damage mechanics.

Residual Thermo-Creep Deformation of Copper Interconnects by Phase-Shifting SEM Moiré Method

The thermo-creep deformation of interconnects related to the residual stress, directly affects their performance and lifetime. In this paper, we proposed an optical method to measure the residual thermo-creep deformation of copper interconnects. This method takes advantages of grating fabrication and the phase-shifting scanning electron microscope (SEM) moiré method. The residual thermo-creep deformation can be acquired through deformation transformation. A one-way grating with frequency of 5000 lines/mm is fabricated on the surface of the copper line in a focused ion-beam (FIB) system. The principal direction of the grating is along the axis of the copper line. The sample is heated in a high temperature furnace under 90 °C for 70 min. The SEM moiré patterns before and after heating are recorded by a field emission SEM in low vacuum. Through the random phase-shifting algorithm, the residual thermo-creep deformation of the copper interconnect line is found to be 500 με. The cause of the tensile strain is analyzed. This work offers an effective technique for measuring the creep deformation of the film lines.

A New Moiré Grating Fabrication Technique Using Hot Embossing Lithography

Moiré grating is a basic optical component, and can be used in various moiré methods. The conventional grating fabrication technology is based on photolithography and holographic interferometry, however, it requires complex optical components and is very difficult to put into practice. In this study, nanoimprint lithography (NIL), or rather, hot embossing lithography (HEL), is proposed for producing high frequency grating. Compared with silicon mold, holographic moiré grating mold costs less and is not easy to break, thus is chosen to be the mold in HEL. Using this mold and the hot embossing system, the grating structure can be transferred to the polymer after HEL process. Through a number of experiments, the process parameters were optimized and gratings were successfully fabricated. The multi-scale morphology of the fabricated gratings was then characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and moiré interferometry. The microscale images observed by AFM and SEM show the regulate dots with equal spacing and the macroscale moiré patterns illuminate the excellent qualities of fabricated grating in a large area. The successful experimental results demonstrate the feasibility of the grating fabricated by HEL for the moiré measurement.

Digital Image Correlation Study on Micro-Crystal of Poly-Crystal Aluminum Specimen under Tensile Load through SEM

In this study, the digital image correlation method(with Newton-Raphson iteration method) is used to measure the in-plane deformation of poly-crystal aluminum. When the specimen is exerted a tensile load, the strain distribution of the specimen surface will be inhomogeneous. The micro-deformation of the poly-crystal aluminum is studied under a SEM(scanning electron microscope), a series of images of the micro crystal are captured during the loading process. By using digital image correlation to analyze the images, the displacement and strain of a micro-crystal are obtained, which provide important data for further analysis of the inhomogeneous properties of the poly-crystal aluminum.

The Technique for Fabricating Submicron Moiré Grating Using FIB Milling

In this study, focused gallium ion (Ga+) beam is utilised to fabricate micro/submicron spacing gratings on specimen surface. The grating types include: parallel, cross, and hybrid (grating with double-frequency). Several hybrid gratings with double frequency were produced in combination mode or superposition mode, which have a good potential to measure deformation within different range. Techniques for producing different type of gratings are discussed in detail. As an application, a 5000 lines/mm grating was fabricated on an amorphous SIC MEMS cantilever and was successfully used to measure its virtual strain with aid of digital moiré. The experimental results verify the feasibility of fabricating high frequency grating on metal or non-metal surface using the FIB milling and the resultant grating can be used to measure micro-deformation.

A Study of Creep Properties of Polymer Bonded Explosives

Creep properties of polymer bonded explosives (PBXs), a particulate composite, was studied by using the method of moiré interferometry in this paper. The specimens fabricated by different heat pressing technology were used. Extensive creep deformation of PBXs material was indirectly measured by the aid of compressive circular disk test. The obtained results shown that creep properties are greatly influenced by pressing pressures and temperature of heat pressing technology. The results indicated that the higher the temperature and the pressing pressure are in the heat pressing technology to some degree, the better the PBXs material creep resistance is. The creep fracture surfaces of PBXs were also observed using Scanning Electronic Microscopy (SEM). It was shown that most of the fracture crack was initiated and propagated along the explosives crystal surface during creep.