Single crystal growth of KNbO3 and application to surface acoustic wave devices

Potential Advantage of Multiple Alkali Metal Doped KNbO3 Single Crystals

“…It is known to be difficult to grow its bulk single crystals from melt due to KN's incongruent melting and the double solid-state phase transformation properties, such as OPEN ACCESS its cubic structure above 435 °C, tetragonal below it, and then at 225 °C turning orthorhombic [6]. In recent years, however, the KN crystal has been a focus of growing interest for piezoelectric applications due to its large electric-mechanical coupling factor, which exceeds 50%, and zero temperature coefficients near room temperature [7,8]. The most important application is a surface acoustic wave (SAW) filer for television receivers and mobile phones [7,8].…”

“…In recent years, however, the KN crystal has been a focus of growing interest for piezoelectric applications due to its large electric-mechanical coupling factor, which exceeds 50%, and zero temperature coefficients near room temperature [7,8]. The most important application is a surface acoustic wave (SAW) filer for television receivers and mobile phones [7,8]. In the KN crystal for example, 70% kt (electromechanical coupling factor for the thickness-extensional mode) was reported by 49.5° rotated X-cut about the Y-axis [9,10].…”

“…The KN crystal can be grown with high quality and low lattice defects, especially in fiber shape [11]. It is difficult, however, to grow large size and high quality crystals since the melting mode of the KN crystal is incongruent [7]. The most common growth technique for the KN crystal in bulk shape is the top-seeded solution growth (TSSG) method [1][2][3][4][5].…”

MOCVD of KNbO3 Ferroelectric Films and their Characterization

“…[3,4] Unfortunately, optical and acoustic applications of KNbO 3 are strongly restricted by the severe technological difficulties of single-crystal growth from flux, and subsequent conversion into single-domain state.…”

“…The major problem that makes separate evaporation necessary is the difference in melting points of commonly used precursors: potassium 2,2,6,6-tetramethylheptanedionate-3,5 (K(thd) T melt = 185 C) and niobium alkoxides (commonly used Nb(OEt) 5 T melt = 6 C), as well as their tendency to cross-exchange ligands. Nb(thd) 4 , possessing a higher melting point, is also known as an alternative Nb precursor, however it is expensive and susceptible to oxidizing hydrolysis, because of the low valence state of Nb. At the same time, alkoxide heteroligand metal complexes, where one or more ligands form chelate cycles, are more stable to hydrolysis than alkoxides.…”