The optical, structural, and electrical characteristics of aluminum oxide thin films deposited by pulsed ultrasonic sprayed pyrolysis are reported. The films are deposited on crystalline silicon at temperatures from 400to550°C using a chemical solution of aluminum acetylacetonate, as source of aluminum, and N, N-dimethylformamide, as solvent. A H2O–NH4OH mist is supplied simultaneously during deposition to improve the films’ properties. The results showed that the properties of the as deposited films depended strongly on the number of pulses used and on the substrate temperature. The thickness of the films is under 300Å and the best films’ properties showed an index of refraction close to 1.6 and a root mean square surface roughness of about 7.5Å in average. Infrared spectroscopy shows that SiO2 is observed at the interface with silicon of the Al2O3 films and seemed to play, as expected, a dramatic role in the electrical characteristics of the interface. Films with a dielectric constant higher than 8 and an interface trap density at midgap in the 1010eV−1cm−2 range are obtained. Films deposited with three pulses and at 550°C are able to stand an electric field up to 4MV∕cm.
Y 2 O 3 films were deposited on c-Si substrates at temperatures in the 400–550°C range, with no further thermal treatment given to these samples, using the spray pyrolysis technique. The spraying solution was yttrium acetilacetonate disolved N,N-dimethylformamide. In addition, a solution of H2O–NH4OH was sprayed in parallel during the deposition process to improve the optical, structural, and electrical properties of the deposited films. The growth of a SiO2 layer between the yttrium oxide and the Si substrate during this deposition process resulted in interface state density values as low as 1010eV−1cm−2. An effective refractive index value of 1.86, and deposition rates close to 1Å∕s were obtained. The Y2O3 films were polycrystalline with a crystalline cubic phase highly textured with the (400) direction normal to the Si surface. An effective dielectric constant up to 13, as well as a dielectric strength of the order of 0.2MV∕cm was obtained for ∼1000Å thick as-deposited films incorporated in a metal-oxide-semiconductor structure.
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