Graduation Semester and Year

2008

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Dan Popa

Abstract

Microelectromechanical systems (MEMS) is an enabling technology for miniaturization. MEMS consist of micron sized moving mechanical structures and electronics fabricated on a suitable substrate such as silicon. MEMS has found applications in virtually every aspect of human life, ranging from the automobile to the aerospace, and from the telecommunications to the consumer electronic industries. Technology integration has led to several subsets of MEMS e.g. microoptoelectromechanical systems (MOEMS), radio-frequency MEMS (RF MEMS), etc. Together with these added functionalities, by way of technology integration come additional issues and challenges never before experienced by packaging engineers. MEMS and MOEMS package requirements vary widely with the application, but they generally involve protecting the device from the damaging effects of the environment, such as moisture, dust, vibrations or thermal shock. In this dissertation, we applied Design for Reliability (DfR) principles to MOEMS packaging especially at the process development stage of product actualization. DfR provides a unique approach to MOEMS packaging with reliability as the focal point. Such an approach is desirable for several reasons. First, it reduces the cost and time for product development by departing from the "build-test-rebuild" approach. Secondly, it provides better understanding of the process input-output relationship so the practitioner is better able to make informed design decisions. Lastly, this can lead to enhanced product quality, performance and reliability. The DfR framework for MEMS packaging was demonstrated using demanding MEMS application devices - two MEMS based optical switches and a micropump. The reliability requirement for the optical switches are stringent - namely, a shelf-life of 25 years or more, requiring hermetic sealing through the use of metal seals, and no organic compounds inside the package. Numerical simulation and experiments were used systematically in order to guide the process design for the different packaging processes discussed in this dissertation. These processes include fluxless die-to-carrier attachment, optical fiber-to-carrier attachment, and hermetic lid sealing. Results show that this packaging approach is very helpful in determining adequate process windows using only a small number of reliability experiments, leading to a shorter production development cycle for the MOEMS device. Another MEMS device discussed in this dissertation is the MEMS based micropump for implantable drug delivery. The packaging of this class of MEMS device requires hermetic sealing, biocompatibility and adequate thermal management for implantation in the body. Numerical simulation and experiments were used systematically in order to guide the package design process for the micropump. We show that packaging greatly influences the performance of the micropump, and therefore design optimization of the package is necessary. The reduced order model is accurate enough to capture the heat dissipation trends in the micropump to within 6%, however, it only requires fraction of simulation time compared to a full fledged FEA analysis. The model is then used to modify the package materials and geometry in order to ensure a safe operating temperature for an implanted micropump in the human body. Our approach can be used for the analysis of packaged electrothermal MEMS actuators in general.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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