Effects of annealing on the structure and electrical conductivity of CVD alumina films

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Abstract
Alumina films, 160 nm thick, were deposited on (100) -oriented silicon single-crystal substrates by pyrohydrolysis of aluminum chloride. Such films are candidate gate materials for an improved pH ion-sensitive field-effect transistor (pH-ISFET) for industrial and medical pH measurements. The current-voltage (I–V) characteristics of films annealed for 30 min at temperatures of 850, 1000, and 1175 °C were determined, Annealing at 850 °C produced the optimum I–V behavior for the aluminum oxide pH-sensitive films as evidenced by minimum leakage current and maximum breakdown voltage. The structures of the annealed films were examined using transmission electron microscopy. The anneals at 1000 and 1175 °C caused partial and complete transformation, respectively, of the as-deposited α-alumina to the α-alumina phase. Associated with a-alumina formation was the creation of voids along the grain boundaries and in the grain interiors that provided paths of increased electrical conduction through the alumina films and degraded their dielectric behavior.

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