Microelectromechanical Systems Materials Testing and Quality Assurance System, 18-9170

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Principal Investigators
Stephen J. Hudak Jr.
Daniel P. Nicolella
Scott R. Runnels

Inclusive Dates: 11/03/99 - Current

Background - For microelectromechanical systems (MEMS) to develop into a thriving nano-technology over the next 10 to 15 years, several technological problems must be solved. Although advances in design, manufacturing, and packaging need to continue, these technologies are, in many ways, ahead of other required technologies since they are based on adaptations of the preexisting microelectronics technology. One such fundamental barrier is the development of novel methods for accurate and cost-effective measurement of material properties needed in MEMS design. Simply stated, both solids and fluids take on perplexing new properties at the microscopic scale. As the size scale is reduced, surface effects begin to dominate the material response; consequently, bulk properties measured on larger specimens are no longer valid. Properties may also deviate from bulk values as the characteristic size of the device approaches the size scale of material microstructural features, for example, the grain size in polycrystalline materials such as silicon. Finally, the properties of MEMS are known to be very sensitive to defects. These defects can arise from airborne impurities or from the manufacturing process itself. Therefore, novel methods of measuring basic properties on the micro scale, as well as characterizing the influence of inherent material defects on the structural integrity of MEMS devices, are needed before this technology can be reliably implemented. The challenge is to be able to measure these properties at the microscopic scale in a cost-effective manner.

Approach - The goals and systematic approach to this research are as follows: 1) to develop methods for measuring material properties on the microscopic level using an atomic force microscope and a microindentor device; 2) to verify computational tools used to design MEMS by comparing computational predictions with microscopic measurements of strain and displacement using steroimaging measurements in a scanning electron microscope; 3) to use the above information to develop a laboratory on a chip for cost-effective material property measurements; 4) to verify the utility of the laboratory on a chip by comparing results with independent measurements using the techniques in 1) above; and 5) to define the applicability of these measurements to durability assessment and quality assurance of MEMS.

Accomplishments - In the first year of this two-year project, polysilicon microbeams were fabricated by SwRI's industrial partner IntelliSense, and initial elastic modulus measurements have been made with SwRI's atomic force microscope (AFM). These measurements identified the need to improve the accuracy of the measurements by accounting for, or eliminating, the torsional response of the AFM probe, as well as by better calibrating the AFM probe, using single-crystal silicon calibration standards of known modulus. With respect to the laboratory on a chip, a conceptual design for a novel and cost-effective method of making elastic modulus measurements has been developed, and patent applications are in progress.

Materials Research and Structural Mechanics Program
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