Peter Hefti

Miniaturization as a key factor to the development and application of advanced metrology systems

Recent technological advances of miniaturization engineering are enabling the realization of components and systems with unprecedented capabilities. Such capabilities, which are significantly beneficial to scientific and engineering applications, are impacting the development and the application of optical metrology systems for investigations under complex boundary, loading, and operating conditions. In this paper, and overview of metrology systems that we are developing is presented. Systems are being developed and applied to high-speed and high-resolution measurements of shape and deformations under actual operating conditions for such applications as sustainability, health, medical diagnosis, security, and urban infrastructure. Systems take advantage of recent developments in light sources and modulators, detectors, microelectromechanical (MEMS) sensors and actuators, kinematic positioners, rapid prototyping fabrication technologies, as well as software engineering.

Hybrid Methodology for Development of MEMS

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 their integration and packaging. 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 packaged to facilitate their use. MEMS packaging, however, is application specific and, usually, has to be developed on a case by case basis. To facilitate advances of MEMS, educational programs have been introduced addressing all aspects in their development. This paper presents a hybrid methodology addressing various aspects in a development of MEMS including, but not limited to, design, analysis, fabrication, characterization, packaging, and testing. The presentation is illustrated with selected examples from development of specific MEMS.

A Metal Interposer for Isolating MEMS Devices from Package Stresses

Many classes of MEMS devices, such as those with resonant structures, capacitive readouts, and diaphragm elements, are sensitive to stresses that are exerted by their surrounding package structure. Such stresses can arise as a result of changes in temperature, ambient pressure, or relative humidity. We have demonstrated a dramatic reduction in scale factor bias over temperature for a tuning fork gyroscope by mounting it on an interposer structure within a conventional chip carrier, Fig. 1. Optimization of a MEMS sensor package for high performance subject to various constraints cannot be accomplished by analysis alone Hanson et al. [1]. There are too many unknown parameters, e.g., material properties, process conditions, and components/package interface conditions, to make this feasible. Extensive performance evaluation of packaged sensors is also prohibitively expensive and time consuming. However, recent advances in optoelectronic laser interferometric microscope (OELIM) methodology Furlong and Pryputniewicz [2] offer a considerable promise for effective optimization of the design of advanced MEMS components and MEMS packages. Using OELIM, sub-micron deformations of MEMS structures are readily measured with nanometer accuracy and very high spatial resolution over a range of environmental and functional conditions. This greatly facilitates characterization of dynamic and thermomechanical behavior of MEMS components, packages for MEMS, and other complex material structures. In this paper, the OELIM methodology, which allows noninvasive, remote, full-field-of-view measurements of deformations in near real-time, is presented and its viability for development of MEMS is discussed. Using OELIM methodology, sub-micron displacements of sensors can be readily observed and recorded over a range of operating conditions, Fig. 2.

Development of nondestructive testing/evaluation methodology for MEMS

Development of MEMS constitutes one of the most challenging tasks in todays micromechanics. In addition to design, analysis, and fabrication capabilities, this task also requires advanced test methodologies for determination of functional characteristics of MEMS to enable refinement and optimization of their designs as well as for demonstration of their reliability. Until recently, this characterization was hindered by lack of a readily available methodology. However, using recent advances in photonics, electronics, and computer technology, it was possible to develop a NonDestructive Testing (NDT) methodology suitable for evaluation of MEMS. In this paper, an optoelectronic methodology for NDT of MEMS is described and its application is illustrated with representative examples; this description represents work in progress and the results are preliminary. This methodology provides quantitative full-field-of-view measurements in near real-time with high spatial resolution and nanometer accuracy. By quantitatively characterizing performance of MEMS, under different vibration, thermal, and other operating conditions, specific suggestions for their improvements can be made. Then, using the methodology, we can verify the effects of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS, which will ensure that they are operated at optimum performance, are durable, and are reliable.

Optoelectronic Methodology for Development of MEMS

Development of microelectromechanical systems (MEMS) constitutes one of the most challenging tasks in today’s micromechanics. In addition to design, analysis, and fabrication capabilities, this task also requires advanced test methodologies for determination of functional characteristics of MEMS to enable refinement and optimization of their designs. Until recently, this characterization was hindered by lack of a readily available methodology. However, building on recent advances in photonics, electronics, and computer technology, we have developed an optoelectronic methodology particularly suitable for development of MEMS. In this paper, we describe the optoelectronic methodology and illustrate its use with representative examples. By quantitatively characterizing performance of MEMS, under different vibration, thermal, and other operating conditions, we can make specific suggestions for their improvements. Then, using the optoelectronic method, we can verify the effects of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS, which will ensure that they are operated at optimum performance, are reliable, and are durable.Copyright

Measurement and Modeling of MEMS

Advances in MEMS, also called microsystems, require the use of computational modeling and simulation with physical measurements, i.e., measurements and modeling (M&M) approach is needed. We believe that successful combination of computer aided design (CAD) and multiphysics/multiscale simulation tools with the state-of-the-art (SOTA) measurement methodology will contribute to reduction of high prototyping costs, minimization of long product development cycles as well as time-to-market pressures while developing MEMS for various applications. In our approach we combine a unique, fully integrated, software environment for multiscale, multiphysics, high fidelity analyses of MEMS with the SOTA optoelectronic laser interferometric microscope (OELIM) methodology. The OELIM methodology allows remote, noninvasive, full-field-of-view measurements of deformations with very high spatial resolution, nanometer accuracy, and in near real-time. In this paper, both, the software environment and the OELIM methodology are described and their applications are illustrated with representative results demonstrating viability of the M&M approach to the development of MEMS. These preliminary results demonstrate capability of the M&M approach to quantitatively determine effects that static and dynamic loads have on the performance of MEMS.Copyright

Modal Response of Polymers With SMA Ribbon Reinforcements

Shape Memory Alloy (SMA) based composites are unique because their static and dynamic characteristics can be controlled. Active modal modification and active strain energy tuning are two common techniques used to control the dynamics of SMA based composite materials. Using Active Modal Modification Technique (AMMT), the stiffness of the SMA composite can be modified by changing the temperature of the SMA. The stiffness change is a result of a reversible phase transformation, which is tempeature activated. The Active Strain Energy Tuning Method (ASETM) takes advantage of the SMA’s ability to impart forces to the structure thereby changing the stored strain energy within the composite. The result is a change in the modal characteristics of the composite material. This paper will present the results of the application of an AMMT used to modify the dynamic characteristics of an SMA composite. A rectangular example of quasi-isotropic SMA composite was used in this study. As a result of a temperature change, the stiffness of the composite changed. This change is stiffness altered the dynamic responses such as the resonant frequency of the composite. Time Average Opto-Electronic Holography (TAOEH) [6] was used to monitor the dynamic behavior of the structure. Analytical modeling was used along with the experimental results to obtain the temperature history of the composite as a result of the activation of the SMA.Copyright