Extraction of electromechanical coupling coefficient of piezoelectric thinfilms deposited on substrates

A method to extract the electromechanical couplig coefficient k(t)(2) of th e thickness extensional mode of a piezoelectric thin film deposited on a su bstrate is presented, in which a two-layer structure is as a composite reso nator. Based on the method proposed by Wang et al. (IEEE Trans. UFFC 46 (19 99) 1327), we present two alternative approximate equations of k(t)(2), the n k(t)(2) can be calculated directly from the effective electromechanical c oupling factor k(eff)(2). of two special modes of the composite resonator. The new method is unnecessary to know the thickness of the piezoelectric fi lm, which is very difficult to accuracy measure for a high frequency compos ite resonator or transducer. The accuracy and validity of this method are c hecked by numerical simulation on two typical samples. The results of numer ical simulation show that the proposed approximate method is available for a real piezoelectric thin film, if the mechanical loss in the film is less than 5% and the mechanical loss in the substrate is less than 0.8%. (C) 200 1 Elsevier Science B.V. All rights reserved.