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Abstract
Aqueous chemical solution deposition (CSD) of lead-free ferroelectric K0.5Na0.5NbO3 (KNN) thin films has a great potential for cost-effective and environmentally friendly components in microelectronics. Phase purity of KNN is, however, a persistent challenge due to the volatility of alkali metal oxides, usually countered by using excess alkali metals in the precursor solutions. Here, we report on the development of two different aqueous precursor solutions for CSD of KNN films, and we demonstrate that the decomposition process during thermal processing of the films is of detrimental importance for promoting nucleation of KNN and suppressing the formation of secondary phases. Based on thermal analysis, X-ray diffraction and IR spectroscopy of films as well as powders prepared from the solutions, it was revealed that the decomposition temperature can be controlled by chemistry resulting in phase pure KNN films. A columnar microstructure with out-of-plane texturing was observed in the phase pure KNN films, demonstrating that the microstructure is directly coupled to the thermal processing of the films.
Highlights
Piezoelectric K0.5 Na0.5 NbO3 -based (KNN) ceramics have been extensively studied the last decade to replace the state-of-the-art piezoelectric materials based on PbZrx Ti1−x O3 (PZT) [1,2,3].In addition to the environmental advantage of being lead-free, KNN-based ceramics benefit from having relatively high piezoelectric coefficients [4] and high Curie temperatures [1]
A persistent challenge in chemical solution deposition (CSD) synthesis of KNN thin films is the formation of alkali metal deficient secondary phases, most notably K4 Nb6 O17
KNN thin films were successfully prepared by spin coating using both precursor solutions
Summary
Piezoelectric K0.5 Na0.5 NbO3 -based (KNN) ceramics have been extensively studied the last decade to replace the state-of-the-art piezoelectric materials based on PbZrx Ti1−x O3 (PZT) [1,2,3].In addition to the environmental advantage of being lead-free, KNN-based ceramics benefit from having relatively high piezoelectric coefficients [4] and high Curie temperatures [1]. Fabrication of KNN thin films for incorporation in electronic devices has been investigated [7,8,9]. Preparation of thin films of KNN has successfully been performed by physical vapor deposition (PVD) [10,11] and chemical vapor deposition (CVD) [12,13]. Fabrication of KNN thin films by chemical solution deposition (CSD) has been targeted, and 2-methoxyethanol based solutions with cation ethoxides and acetates are by far the most used, giving KNN thin films with varying degree of texture [7,14,15,16,17,18,19,20,21,22,23,24,25]. A persistent challenge in CSD synthesis of KNN thin films is the formation of alkali metal deficient secondary phases, most notably K4 Nb6 O17. Measures to avoid formation of such parasitic phases are usually
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