Growth of Li2B4O7 films on LiNbO3 and LiTaO3 substrates

Lithium niobate (LiNbO
₃
: LN) and lithium tantalate (LiTaO
₃
: LT) are widely used for bulk and surface acoustic wave devices because of their excellent piezoelectricity and high mechanical Q-factors. However, the frequency temperature coefficients (TCF) of these crystals are relatively large. On the contrary, lithium tetraborate (Li
₂
B
₄
O
₇
: LBO) has high piezoelectricity and a positive TCF. We investigated a method of growing LBO single crystal films on LN and-/or LT substrates in order to achieve piezoelectric substrates with high electromechanical coupling and low TCF.