Dr. Wei Han Profile

Dr. Wei Han

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Proceedings Article | 19 January 2007 Paper

Hybrid approach to MEMS reliability assessment

James Zunino, Donald Skelton, Wei Han, Ryszard Pryputniewicz

Proceedings Volume 6463, 646304 (2007) https://doi.org/10.1117/12.700697

KEYWORDS: Microelectromechanical systems, Reliability, Switches, Sensors, Packaging, Optoelectronics, Microscopes, CCD cameras, Fringe analysis, Nanolithography

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Recent advances in MEMS technology have led to development of a multitude of new devices. However applications of these devices are hampered by challenges posed by limited understanding of their reliability particularly the impacts of long-term storage. Current trend in micro/nanosystems is to produce ever smaller, lighter, and more capable devices in greater quantities and at a lower cost than ever before. In addition, the finished products have to operate at very low power and in very adverse conditions while assuring durable and reliable performance. Some of the new devices are being developed to function at high operational speeds, others to make accurate measurements of operating conditions in specific processes. Regardless of their application, the devices have to be reliable while in use. MEMS reliability, however, is application specific and, usually, has to be developed on a case by case basis. This paper presents a hybrid approach/methodology particularly suitable to quantitative studies of various aspects in MEMS reliability assessment. The presentation is illustrated with selected examples representing an initial study of reliability of specific MEMS. By quantitatively characterizing performance of MEMS, under different operating conditions, we can make specific suggestions for their improvements. Then, using the hybrid approach/methodology, we can verify the effect of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS sensors, which will ensure that these sensors are operated at maximum performance, are durable, and are reliable.

Proceedings Article | 29 September 2004 Paper

Investigations of laser percussion drilling of small holes on thin sheet metals

Wei Han, Ryszard Pryputniewicz

Proceedings Volume 5525, (2004) https://doi.org/10.1117/12.560253

KEYWORDS: Laser drilling, Pulsed laser operation, Metals, Laser processing, Liquids, Plasma, Laser energy, Nd:YAG lasers, Absorption, Reflectivity

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Laser drilling is increasingly being used in fabrication of small components for electronics, aerospace, biomedical, and MEMS applications because it provides rapid, precise, clean, flexible, and efficient process. For laser percussion drilling, the workpiece is subjected to a series of laser pulses at the same spot at a specified laser parameter setting. Large temperature gradient is introduced, which results in a minimal heat affected zone (HAZ) and low heat distortion. In laser percussion drilling of small holes, profile of the HAZ and the geometry of the holes strongly depend on settings of the laser parameters such as peak power, pulse length, pulse repetition rate, focal condition, number of pulses, etc. In addition, the processing results are strongly influenced by geometrical and material properties of the workpiece. This paper presents a study of laser process for percussion drilling of micrometer size holes on thin sheet metals using a pulsed Nd:YAG laser. Experimental investigations are performed to characterize the geometry of the hole and surface topography in their vicinity. Analytical and computational modeling of the temperature distribution is also performed and used to determine profiles of the HAZs. The effects of different combinations of laser parameters and workpiece properties on the hole geometry are summarized and a procedure for laser percussion drilling of small holes on sheet metals is outlined.

Proceedings Article | 2 August 2004 Paper

Nondestructive evaluations of thermal deformations for laser microwelding process

Wei Han, Ryszard Pryputniewicz

Proceedings Volume 5532, (2004) https://doi.org/10.1117/12.560273

KEYWORDS: Laser processing, Fringe analysis, Nondestructive evaluation, Holography, Laser development, Laser applications, Optoelectronics, Image processing, Laser welding, Laser energy

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Laser microwelding process produces large temperature gradients during the complicated phase transformations of workpiece materials, which results in a high stress level and undesired thermomechanical deformations. Characterization of these deformations becomes important as they might significantly affect performance, functionality, and reliability of the microwelded components. We have developed an optoelectronic holography (OEH) methodology for nondestructive evaluation of thermomechanical deformations caused by laser microwelding processes. OEH methodology provides a unique experimental approach for quantitative measurements of displacements and deformations with sub-micrometer accuracy in full field of view. In this paper, the OEH methodology is described including illumination of a workpiece, formation and acquisition of images, and processing of these images to determine parameters characterizing laser microwelds. Representative results of the OEH measurements of the deformations caused by laser microwelding of metal sheets are presented as a function of different laser welding parameters. In addition, analytical and computational models are also developed to simulate temperature, thermal stress, and thermal deformation fields in laser microwelding process. The investigations indicate that the OEH methodology is a viable tool for characterization of thermomechanical deformations caused by laser microwelding processes, and can help optimizing laser microwelding processes for high precision material-joining applications.

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