Optimization of LiNbO3 based surface acoustic wave (SAW) device substrates by magnesium and titanium doping

Abstract

Lithium niobate (LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">₃</inf>, or LN) is a versatile material widely used in the development of acoustic devices. This study examines the effects of titanium (Ti⁴⁺) and magnesium (Mg<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>⁺) doping on the Curie temperature (Tc) and inverse quality factor (Q⁻¹) of LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">₃</inf>. Using a modelling approach based on ferroelectric phase transition theory, we investigated how varying impurity concentrations influence Tc and Q⁻¹. Our simulations show that at low doping levels, Mg<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>⁺ increases both Tc and Q⁻¹ up to a critical threshold of approximately 3.4%, beyond which Q⁻¹ begins to decrease. Conversely, Ti⁴⁺ doping causes a gradual decrease in Tc and Q⁻¹ as the concentration increases, resulting in an improvement in the quality factor (Q). These results highlight the importance of choosing the type of dopant according to thermal conditions: Ti⁴⁺-doped LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">₃</inf> is more suitable for moderate temperatures, while Mg<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>⁺-doped LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">₃</inf> is preferable for high-temperature environments, particularly when used as a substrate in surface acoustic wave (SAW) resonators.