Synthesis of an effective interlayer between a functional oxide film and Si₃N₄ substrate

Abstract

Laminated CuO/Al₂CuO₄/CuO layers were developed to serve as an interlayer between the conducting oxide CaCu₃Ru₄O₁₂ + 30 vol.% CuO and nitride substrate Si₃N₄. Screen-printing was used to fabricate these films. The Al₂CuO₄ layer impeded the chemical reaction between CaCu₃Ru₄O₁₂ and Si₃N₄ and hence suppressed the decomposition of CaCu₃Ru₄O₁₂. The CuO interlayers improved the adhesion between the Si₃N₄ substrate, Al₂CuO₄ layer, and CaCu₃Ru₄O₁₂ + 30 vol.% CuO film. The main difference between the CaCu₃Ru₄O₁₂ + 30 vol.% CuO film on the Si₃N₄ and Al₂O₃ substrates having the same interlayers was the presence of a small amount of RuO₂ (formed from decomposition of CaCu₃Ru₄O₁₂) and cracks in the film on the Si₃N₄ substrate. The difference in the coefficients of thermal expansion between the Si₃N₄ substrate, interlayers, and film caused cracks to appear when the temperature of the film decreased after sintering. The resistivities of the films on the Si₃N₄ and Al₂O₃ substrates were 7 and 3 mΩ·cm at 100 °C, respectively. The film on the Si₃N₄ substrate exhibited higher resistivity than the film on the Al₂O₃ substrate from room temperature to 600 °C. This is because the cracks on the film on the Si₃N₄ substrate scattered the charge carriers. A decrease in crack width with increasing temperature was also observed, which in turn decreased the resistivity of the film with temperature. The conducting properties of the film developed in this work are adequate for practical applications. However, the interlayer can be further improved to obtain films with better performance. The major achievement of the present study is the development of an interlayer that suppresses the chemical reactions between the functional oxide and nitride substrate during high-temperature sintering.