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Glass materials have a random, liquid-like (non-crystalline) molecular structure. They are heated to a temperature sufficient to produce a completely fused melt. Raw materials for glass include cullet (crushed, recycled glass), sand, soda ash, limestone, and additives. At ordinary temperatures, glass materials are relatively strong, inert, biologically inactive, and corrosion resistant. They also provide excellent thermal and electrical insulation, and are characterized by high dielectric strength. During the fabrication of glass materials, the properties of glass can be modified as necessary by additives or heat treatment. Glass materials include embedded glass, tempered glass, borosilicate glass, and soda lime glass. Embedded glass refers to glass materials that are embedded with wire for resistance heating or reinforcement. Tempered glass provides increased strength and can shatter into small pieces when broken. Borosilicate glass offers superior durability, chemical resistance, and heat resistance. These properties make borosilicate glass suitable for use in chemical processes, in the pharmaceutical industry, in high-powered lamps, and in cookware and other heat-resistant products. Soda lime glass is used in everyday products such as bottles, jars, drinking glasses, and window glass.

Lead glass, electronic glass, opal glass, and fused silica glass are types of glass materials. Lead glass (also called lead-alkali glass) has a high percentage of lead oxide (at least 20%) to increase its index of refraction. Lead glass is relatively soft, a better electrical insulator than soda-lime or borosilicate glass, and used for optical applications such as prisms and lenses. Electronic glass is used in fabricating electronic components such as X-ray tubes, display devices, and chip components. Opal glass is used to diffuse light uniformly. Fused silica glass has excellent resistance to thermal shock, withstands high operating temperatures (1,200° C for short periods), and is used in optical waveguides and crucibles for growing crystals.

Several organizations maintain standards for glass materials. ASTM International (formerly called the American Society for Testing and Materials (ASTM) Technical Committee C14 on Glass and Glass Products maintains several standards, including ASTM E708-79(1999) Standard Specification for Waste Glass as a Raw Material for the Manufacture of Glass Containers. The International Organization for Standardization (ISO) supports Technical Committees on glass materials, including TC 48 on quality of glassware and TC 160 on glass in building.

Engineers and researchers designing and building new microelectromechanical systems (MEMS) can benefit from a new test method developed at the National Institute of Standards and Technology (NIST) to measure a key mechanical property of such systems: elasticity. The new method determines the “Young’s modulus” of thin films not only for MEMS devices but also for semiconductor devices in integrated circuits.

Since 1727, scientists and engineers have used Young’s modulus as a measure of the stiffness of a given material. Defined as the ratio of stress (such as the force per unit area pushing on both ends of a beam) to strain (the amount the beam is deflected), Young’s modulus allows the behavior of a material under load to be calculated. Young’s modulus predicts the length a wire will stretch under tension or the amount of compression that will buckle a thin film. A standard method to determine this important parameter — a necessity to ensure that measurements of Young’s modulus made at different locations are comparable — has eluded those who design, manufacture and test MEMS devices, particularly in the semiconductor industry.

A team at NIST recently led the effort to develop SEMI Standard MS4-1107, “Test Method for Young’s Modulus Measurements of Thin, Reflecting Films Based on the Frequency of Beams in Resonance.” The new standard applies to thin films (such as those found in MEMS materials) that can be imaged using an optical vibrometer or comparable instrument for non-contact measurements of surface motion. In particular, measurements are obtained from resonating beams — comprised of the thin film layer — that oscillate out-of-plane. The frequency at which the maximum amplitude (or velocity) of vibration is achieved is a resonance frequency, which is used to calculate the Young’s modulus of the thin film layer. The group also developed a special Web-based “MEMS calculator”  (http:// www.eeel.nist.gov/812/test-structures/MEMSCalculator.htm) that can be used to determine specific thin film properties from data taken with an optical interferometer.

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