6E-5 High Performance and Miniature Surface Acoustic Wave Devices with Excellent Temperature Stability Using High Density Metal Electrodes

Abstract

Currently, miniature surface acoustic wave (SAW) devices (filters and duplexers) with a good temperature stability are strongly required. In order to realize its requirement, various SAW substrates combining a high density metal electrode and a substrate were researched. Combination of SAW substrates using high density metal electrodes offers excellent properties such as large electrode reflection coefficient, large mechanical coupling factor, low velocity, and good temperature stability. This paper reviews following application of their structures for the realization of miniature SAW devices with low insertion loss and good temperature stability from various aspects: Intermediate frequency (IF) filters in mobile phones using an shear horizontal (SH) wave propagating on the high density metal electrode on ST-90 • X quartz substrate, SAW duplexers for personal communication service system in the United States (US-PCS) and wide band code division multiple access system (W-CDMA) using LSAW on a flattened SiO 2 film on high density metal electrodes on LiTaO 3 or LiNbO 3 substrates, and radio frequency (RF) filters using SH type of elastic boundary wave (EBW) propagating on SiO 2 film on high density metal electrode on LiNbO 3 . I. INTRODUCTIONSurface acoustic wave (SAW) devices such as filters at the intermediate frequency (IF) and radio frequency (RF) circuits and duplexers have been playing important role as key devices in a mobile phone system and so on [1]. The mobile phone is strongly required to be small-sized and then SAW devices are also required to be smaller-sized. To realize them, SAW substrates combining a high density metal electrode and a piezoelectric substrate have been investigated. The author has succeeded in exciting various SAWs having large electromechanical coupling factor, large reflection coefficient, and excellent temperature stability, by combining high density metal electrode such as tantalum (Ta), copper (Cu), and gold (Au) and the various substrates [2][3][4][5][6][7][8][9][10][11][12].By applying their features, following various miniature SAW devices such as IF filters, duplexers, and RF filters with good temperature stability and good frequency characteristics were developed.(1) Various IF resoantor filters using shear horizontal (SH) type of leaky SAW (LSAW) generated by Ta electrodes on the ST-cut 90 • X propagation (direction per-

Piezoelectric materials and their applications in radio frequency domain and telecommunications

“…This can be achieved by combining different layers of materials with different properties; this technique enables to reduce the temperature coefficient of frequency down to 5 ppm or less. [19][20][21][22] Nevertheless, SAW filters represent an important part of the market because they are easy to make; moreover, many companies in the world produce them.…”

FEM analysis of wavelength effects in piezoelectric substrate

“…On the other hand, the input energy from the transmitter group in two port SAW device will propagate across the delay line between the two transducers, and detected at the receiver electrodes. SAW devices are widely used in mobile phone technology [1], wireless communication [2], telecommunication [3] and recently, an extensive work focus on biosensor [4], microfluidic [5], microtransport [6] and actuation [7] applications. In this work, we developed a focusing SAW device adopting annular interdigital electrodes to generate high intensity acoustic fields.…”

Theoretical analysis of SAW propagation characteristics in (100) oriented AlN/diamond structure

“…In addition to a high phase velocity and large K 2 , designing low-loss and miniature SAW devices such as single phase unidirectional transducers (SPUDTs), RF filters and duplexers requires a large reflectivity in the interdigital transducers (IDTs) [8][9][10][11][12][13][14][15]. For example, Kadota et al suggested a reflection coefficient of 0.15 for designing wideband code division multiple access (WCDMA) duplexers [11].…”