The analysis of non-homogeneity of SAW velocity in langasite

Abstract

The research results of the influence of different technology parameters of crystal growth and device manufacturing process on SAW velocity variation on langasite (LGS) wafers O 3" are presented. The wafers were made from crystals grown by the Czochralski method along <00.1> and <01.1> directions. The paper also gives a technology process description of langasite crystal growth along <01.1> direction and of making O 3" wafers. SAW velocity measurements were performed utilizing specially developed test structures. The test structures were also used to estimate the device sensitivity due to electrode thickness and electrode width variations of the manufacturing process.. Advantages of LGS wafers for possible SAW device applications are discussed. Due to good temperature stability and a moderately high electromechanical coupling coefficient, langasite is known as a promising material for SAW devices. The filters on LGS have exhibited better electrical parameters than their analogues on quartz and lithium tantalate. In order to demonstrate a practical filter application on LGS, a SAW filter at the center frequency of 114.99 MHz was designed and realized. The chip fits into a 3.8/spl times/3.8 mm/sup 2/ SMD package. Measured performance is in excellent agreement with the predicted response and the chip size was dramatically reduced compared to the state-of-the-art for this kind of filter.