Bing-Feng Ju

A novel technique for mechanical characterization of thin elastomeric membrane

This paper reports a new method to characterize the mechanical properties, such as the elasticity, of a thin elastomeric film. A sensitive microscope visualization instrument is developed for measuring the deformation of a circular membrane of thickness less than 200 µm, under a constant load. The elastic deformation of the thin membrane was measured laterally. A theoretical model is constructed to quantitatively correlate the elasticity to the deformation profile of the membrane. The good agreement between the experimental and theoretical results facilitates the determination of the elastic modulus of a thin elastomeric membrane.

A novel technique for characterizing elastic properties of thin biological membrane

Abstract We present a new technique to characterize the elastic properties of a thin biological membrane. An effective instrument that embodies video enhanced microscope was developed primarily to provide the capability of simultaneously measuring both the applied force and the resultant displacement of the biological membrane under a central point force. A theoretical linear elastic solution was applied to quantitatively interpret the measured central deflection of the membrane under a central point load. The Young’s modulus of raw and boiled Leghorn egg inner tissue can be easily determined once the applied point load and the central deflection, together with the essential dimensions are known. The viscoelasticity property of natural tissue was manifest in the experiment. The experimental results have verified that the novel technique is applicable to determine the Young’s modulus and other viscoelatic properties of thin biological tissue.

Characterizing viscoelastic properties of thin elastomeric membrane

We present a new method to characterize the viscoelastic properties of a thin polymeric film. A sensitive microscope visualization instrument was used for measuring the time-dependent deformation, i.e. creep, of the circular thin membrane under a constant load. The elastic deformation of the thin membrane was measured laterally. The elastic modulus as a function of time can be explicitly determined by our recently developed equations. A viscoelastic theory, Zener model, was applied to interpret the measured time-dependent deformation of the membrane under various temperatures, and the creep parameters can therefore be quantitatively estimated. The results show the elastic constants and viscosity coefficient of the membrane materials decrease with the increasing temperatures.

Microscopic four-point atomic force microscope probe technique for local electrical conductivity measurement

A micro-four-point probe technique for local electrical conductivity measurement is presented. An atomic force microscope (AFM) probe was fabricated into four parallel electrodes isolated from each other. Electrodes separated by a distance as small as 1.0μm were used to perform the current and electrical potential measurements. This technique is a combination of the principles of the four-point probe method and standard AFM. The equipment is capable of simultaneously measuring both surface topography and local electrical conductivity. Experiments show the microprobe to be mechanically flexible and robust. The repeatable conductivity measurement on the submicron surface of thin aluminum and indium tin oxide films demonstrates the capability of the equipment and its possible extension to characterize microdevices and samples.

Rapid measurement of a high step microstructure with 90° steep sidewall

A prototype STM system with high aspect ratio measurement capability is developed to fulfill accurate profile measurement of a high step microstructure with 90° steep sidewall. Distinguished from the traditional STM, the new system consists of a long range piezoelectric (PZT) actuator with full stroke of 60 μm as Z-direction servo scanner, a specially customized high aspect ratio STM probe with effective tip length of 300 μm, and an X-Y motorized driven stage for planar scanning. A tilt stage is used to adjust the probe-sample relative angle to compensate the evitable non-parallel effects. Based on the new STM system, sample-tilt-scanning methodology is proposed for eliminating the scanning blind region between the probe and the microstructure. A high step microstructure with height of 23 μm, 90° steep sidewall and width of 50μm has been successfully measured. The slope angle of the sidewall has been achieved to be 85° and the step height at the rising edge and the trench depth at the falling edge are both measured to be 22.96 μm. The whole measuring process only spent less than 10 min. It provides an effective and nondestructive solution for the measurement of high step or deep trench microstructures. In addition, this work also opens the way for further study on sidewall roughness and the tip-sample interaction at the edge of the sidewall, which are highly valuable for fabrication and quality control of high step microstructures.

A high-sensitivity biaxial resonant accelerometer with two-stage microleverage mechanisms

This paper presents a design and experimental evaluation of a micro-electro-mechanical system biaxial resonant accelerometer with two-stage microleverage mechanisms. The device incorporates two pairs of double-ended tuning fork resonators coupled to a single proof mass. The two-stage microleverage mechanisms possess a higher amplification factor than single-stage microleverage mechanisms, so that the proposed accelerometer has a high level of sensitivity. In addition, a low level of cross-axis sensitivity is realized because of the decoupling beams. The accelerometer is theoretically analyzed and then simulated in the system level by the finite element method. The device is fabricated in a silicon-on-insulator wafer. The experimental results demonstrate that the average differential sensitivity of the resonant accelerometer is 275 Hz g?1 at a resonant frequency of 290?kHz under a polarization voltage of 5?V. The measured cross-axis sensitivity is lower than 3.4%.

A measurement method of cutting tool position for relay fabrication of microstructured surface

By using the secondary function of a force sensor integrated fast tool servo (FTS) for surface profile measurement, the three-dimensional tip position of a micro-cutting tool in the FTS with respect to the fabricated microstructures was measured without using any additional instrument for realizing the concept of relay fabrication of microstructured surface. It was verified from the experiments for testing the basic performances of tool tip position measurement that the delay of the force feedback control loop of the FTS was a big factor influencing the position measurement accuracy. A bidirectional scanning strategy was then employed to reduce the position measurement error due to the delay of the feedback control loop. Tool tip position measurement experiments by using micro-tools with a nose radius of 100 µm for relay fabrications with sub-micrometer accuracies, including stitching fabrication of a micro-groove line array and filling fabrication of a microlens lattice pattern, were carried out to demonstrate the feasibility of the tool position measurement method.

Indentation of a square elastomeric thin film by a flat-ended cylindrical punch in the presence of long-range intersurface forces

This paper reports an experimental study of the elastic deformation of a 200μm thick microfabricated square membrane with sides ranging from 8.5mmto15mm as indented by a fine cylindrical, flat-ended punch with diameter 500μm in the presence of long-range intersurface forces. An apparatus was constructed to allow simultaneously measurements of the indenter displacement and the applied force. A number of interesting phenomena such as the “jump-into-contact” and the “pull-off” between the membrane and the moving cylinder were observed. A simple theoretical analysis using linear elasticity was adopted to fit the load-displacement curve (compliance) and thus estimated the Young’s modulus of the membrane. The measured parameters are consistent with data reported in literature.

Angular measurement of acoustic reflection coefficients by the inversion of V(z, t) data with high frequency time-resolved acoustic microscopy

For inspection of mechanical properties and integrity of critical components such as integrated circuits or composite materials by acoustic methodology, it is imperative to evaluate their acoustic reflection coefficients, which are in close correlation with the elastic properties, thickness, density, and attenuation and interface adhesion of these layered structures. An experimental method based on angular spectrum to evaluate the acoustic coefficient as a function of the incident angle, θ, and frequency, ω, is presented with high frequency time-resolved acoustic microscopy. In order to achieve a high spatial resolution for evaluation of thin plates with thicknesses about one or two wavelengths, a point focusing transducer with a nominal center frequency of 25 MHz is adopted. By measuring the V(z, t) data in pulse mode, the reflection coefficient, R(θ, ω), can be reconstructed from its two-dimensional spectrum. It brings simplicity to experimental setup and measurement procedure since only single translation of the transducer in the vertical direction is competent for incident angle and frequency acquisition. It overcomes the disadvantages of the conventional methods requiring the spectroscopy for frequency scanning and/or ultrasonic goniometer for angular scanning. Two substrates of aluminum and Plexiglas and four stainless plates with various thicknesses of 100 μm, 150 μm, 200 μm, and 250 μm were applied. The acoustic reflection coefficients are consistent with the corresponding theoretical calculations. It opened the way of non-destructive methodology to evaluate the elastic and geometrical properties of very thin multi-layers structures simultaneously.

Fabrication of a microscopic four-point probe and its application to local conductivity measurement

A microscopic four-point probe for local conductivity measurement is presented. The silicon nitride based atomic force microscope (AFM) probe with a V-shaped two-dimensional sliced structure tip is patterned by using a conventional photolithography method. The probe is then etched to four parallel electrodes isolated from each other, for the purpose of performing current input and electrical potential drop measurement. The newly developed four-point AFM probe not only inherits the function of generating AFM surface topography but also has the capability of characterizing the local conductivity simultaneously. The nano-resolution position control mechanism of AFM allows the probe to scan across micrometer sized areas and create a high spatial resolution map of the in-plane conductivities. Experiments have shown this four-point AFM probe to be mechanically flexible and robust. The repeatable conductivity measurements on the surface of aluminum and indium tin oxide (ITO) thin films indicate the technique, which is based on this four-point AFM probe, has potential application for characterizing devices and materials in microscale.