High temperature stable GHz-range low-loss wide band transducersand filter using SiO2/LiNbO3, LiTaO3

摘要

GHz-range low-loss transducers and filters are required forncommunication systems, especially mobile telephone communicationnsystems. Many types of low insertion-loss transducers and filtersnutilizing the high electromechanical coupling coefficientn(K2) materials such as LiNbO3 andnLiTaO3 have been developed. Unfortunately, these materialsnhave large temperature coefficients of the frequency (TCF). In thisnpaper, SAW substrates with high coupling coefficients and lownpropagation attenuations and small temperature coefficient of frequencynin the GHz-range are theoretically and experimentally investigated. Thenexperimental results show very low propagation loss of 0.02 dB/Λn0 and larger K2 than those of the substrates ofnLiNbO3 and LiTaO3 at the TCF of below -5nppm/°C at 1~2 GHz-range. The low-loss filter results using internalnreflection types of IDT show the insertion loss of about 2.9 dB at 1 GHznand 4.9 dB at 2 GHz under the TCF's of 0 and +20 ppm/°C. Thesenmaterials are applicable for devices at GHz-range becausenSiO2 thickness is very thin such as below 1 Μm and thencenter frequency shift of the filter versus SiO2 thickness isnvery small