Jin-Liang Chen

Dynamic Surface Profilometry and Resonant-Mode Detection for Microstructure Characterization Using Nonconventional Stroboscopic Interferometry

In this paper, an innovative method of automatic resonant-mode detection employing nonconventional stroboscopic interferometry is developed for nanoscale dynamic characterization of microstructures. Considering that a tested microstructure having an individual vibrating excitation source cannot be analyzed directly by the traditional stroboscopic method, an optical microscopy based on new stroboscopic interferometry was established to achieve resonant-mode detection and full-field vibratory out-of-plane surface profilometry of microstructures. To verify the effectiveness of the developed methodology, a crossbridge microbeam was measured to analyze the resonant vibratory modes and full-field dynamic-mode characterization. The experimental results confirm that the dynamic behavior of the microstructures can be accurately characterized with satisfactory mode-detection accuracy and surface profilometry.

Large-scale 3-D profilometer

3-D profilometry, it is necessary to locate the in-focus region of the image and to reconstruct the best 3D profile. A series of images are collected on-the-fly. The contrast and the intensity indices of each region of each image are calculated in the scanning procedure. The proposed method will reconstruct 3D shape from moving platform. The proposed method is applied on some preliminary experiments and it shows that the large-scale 3-D profile reconstruction can be realized.

Innovative automatic resonant mode identification for nano-scale dynamic full-field characterization of MEMS using interferometric fringe analysis

A dynamic 3D nano-scale surface profilometer was successfully developed for novel automatic resonant frequency identification using stroboscopic interferometric principle. With rapid increase in the application of micro electromechanical systems (MEMS) to industries, the needs of accurate dynamic characterization have become a major challenge in design and fabrication. In view of such, an interferometric microscopy was developed using LED stroboscopic interferometry to achieve dynamic full-field profilometry and characterization of MEMS with a measurement bandwidth exceeding 1 MHz. Most importantly, a novel detection algorithm was also developed employing interferogram fringe density measure for automatic resonant frequency identification. Natural resonant modes of a series of microstructures can be accurately detected, giving values consistent with theoretical ones. To verify the effectiveness of the developed methodology, an AFM cantilever microbeam and a cross-bridge microbeam were measured to analyze their full-field resonant vibratory shapes. Our experimental results confirmed that the resonant vibration of the tested beams can be fully characterized while achieving an accuracy in vertical measurement of 3–5 nm with a vertical measurement range of tens of micrometers.

Dynamic Nano-scale Surface Profilometry Using Stroboscopic Interferometry

Dynamic 3-D nano-scale surface profilometry using stroboscopic interferometry was successfully developed. An optical microscopy based on stroboscopic interferometry was developed to achieve full-field vibratory out-of-plane surface profilometry and system characterization. To increase the measurement bandwidth of the developed system, an innovative image processing algorithm based on deconvolution principle was developed to improve the signal to noise ratio of the detected interferometric data. The method provides an excellent way to increase the measurement bandwidth without adding any significant hardware in a stroboscopic interferometric framework. Meanwhile, an innovative detection algorithm based on image contrast measure was developed for automatic identification of accurate resonant modes. To verify the effectiveness of the developed methodology, a cross microbeam was measured to analyze the full-field resonant vibratory modes and dynamic characteristics. The experimental results confirm that the dynamic behavior of the tested microcantilever beams can be accurately characterized and 5 nm of vertical measurement accuracy as well as tens micrometers of vertical measurement range can be achieved. The measured results were satisfactorily consistent with the theoretical simulation outcomes from ANSYS.

Portable Measurement System for Static and Dynamic Characterization of MEMS Component

MEMS performance can be determined from the static and dynamic characteristic. These two parameters can be measured by various measuring systems. In this chapter, a portable measurement system which is able to measure static and dynamic characteristic of MEMS in 2-D and 3-D aspects is presented. Nanoscale static microstructure profiles are measured by means of white-light interferometry with nanometer scale accuracy. Key for dynamic characteristic measurement is the employment of stroboscopic lighting which is synchronized with the excitation signal of the measured sample. The system is capable of measuring multimode resonant frequencies and also mode reconstruction for both in-plane and out-of-plane vibration. The main advantage of the system is its versatility and portability for testing different vibration modes with improved reliability and repeatability. Achievable repeatability of the resonant frequency measurement can reach 0.012 kHz for in-plane vibration, while the repeatability of the out-of-plane resonant frequency is 0.216 kHz for a controlled environment and 0.354 for an environment with disturbance from air conditioner.

Auto-scanning white-light interferometer

This study proposes the auto-focusing procedure and the scan-range determining algorithm for white-light scanning interferometry. During white-light scanning interferometry, the interference fringe must be located and to the best-focus interferogram identified. The vertical-scan range must also be determined prior to the scanning procedure. A series of images, either in-focus or out-of-focus, are collected in a proposed interference-fringe searching step. The contrast and the sharpness indices of each image are calculated and applied in the auto-focusing scheme, and the vertical-scan range is determined accordingly. Some preliminary experiments are performed to demonstrate that the best-focus interferogram can be located precisely and the vertical-scan range can be determined.

A Multifunctional Scanning White-Light Interferometer (SWLI): Construction of 2-D and 3-D Measurements

It is necessary and important to find the focal plane in order to locate where the interference fringe is, and to determine the vertical-scan range prior to the scanning operation for an SWLI. A novel scheme is proposed in this paper for simultaneously carrying out the auto-focusing and the real-time 2-D measurement. Conventionally in a SWLI, it always happens that the interference fringe appears across the focal plane, and therefore the in-focus image is blurred by the interference fringe, which makes it difficult to carry out the auto-focusing and the 2- D measurement with the in-focus image. A multi-function SWLI has been developed such that the 2-D and 3-D measurements can be done simultaneously. Although the 3-D profile reconstruction is basic to an SWLI, the real-time 2-D measurement is not trivial. The proposed scheme is based on clarifying the out-of-focus images where interference fringes do not exist. The proposed scheme is applied on some preliminary experiments and it shows that the real-time 2-D measurement can be realized, and moreover, the accuracy of the 3-D profile reconstruction can also be improved.

Dynamic out-of-plane profilometry for nano-scale full field characterization of MEMS with automatic detection of vibratory modes and MHz-scale measurement bandwidth

A dynamic 3-D nano-scale surface profilometer using stroboscopic white light interferometry with novel image deconvolution and automatic identification of structure resonant modes was successfully developed. As micro electromechanical systems (MEMS) increase rapidly towards industrial application, the needs of accurate dynamic characterization are extremely important to optimal design and fabrication. To meet the demands, an optical microscopy based on stroboscopic interferometry was developed to achieve full-field vibratory out-of-plane surface profilometry and system characterization. A novel deconvolution strategy with correction of the light response function was established to remove the potential image blurs caused by the unavoidable vibration of the tested parts. With this technical advance, the bandwidth of dynamic measurement can be significantly increased up to 10 MHz without sacrificing measurement accuracy. Meanwhile, an innovative detection algorithm based on image contrast measure was developed for automatic identification of accurate resonant modes. The detection method provides the simplest and most economic way to detect accurate resonant peaks without adding any significant hardware in a stroboscopic interferometric framework. To verify the effectiveness of the developed methodology, AFM cantilever beams were measured to analyze the full-field resonant vibratory modes and dynamic characteristics. The experimental results confirm that the resonant vibration behavior of the tested microcantilever beams can be accurately characterized and 5 nm of vertical measurement accuracy as well as tens micrometers of vertical measurement range can be achieved. The measured results were satisfactorily consistent with the theoretical simulation outcomes from ANSYS.