Efforts in this quarter were concentrated on developing vacuum processing procedures to produce thinner (less than 4 (micro)m-thick), defect-free films over larger areas (greater than 100 cm(sup 2)). We continued to test three different types of rigid supporting substrates, thermally oxidized silicon (10 cm diameter), polished borosilicate glass (10 cm diameter), and soda-lime glass (greater than 100 cm(sup 2) areas), each representing a different cost, surface roughness, and chemistry. Mechanical integrity, defect density, and release characteristics of the films, though similar for the oxidized silicon and borosilicate glass, were distinctly different for the inexpensive soda-lime (float) glass; i.e., more sensitive to surface impurities. In general, films less than 4 (micro)m-thick were shown to be very sensitive to surface condition of the supporting substrate, particularly in the case of the soda-lime glass, to the point where surface strain overrode and dominated the intrinsic bulk stresses that are produced during the growth process. Therefore, in the near term (over the next quarter), large area films greater than 100 cm(sup 2) will be produced at a minimum thickness of 5(micro)m while further development will be conducted in subsequent quarters to reduce membrane thickness in large area films.
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