Investigation of new‐mode‐type SAWs by procedures combined with finite‐element and analytical method, and their applications for devices used in mobile communications

Abstract

SUMMARYSimulations using a combination of the finite-element method and the analytical method as well as experiments are used to study new-mode-type SAWs. First, in 171°YZc-LiNbO 3 , it is found that there exists a longitudinal leaky SAW with a high acoustic velocity and a high Q in a grating structure with an Al film thickness of 0.084 wavelength. The acoustic velocity is 6100 to 6500 m/s and the Q values are more than 4000 (computed) at both the resonance and antiresonance points. These excellent properties are suitable for high-frequency SAW devices. Next, in 15°YX-LiNbO 3 , it is found that there exists a grating mode SAW of a transverse wave type in a grating structure with an Al film thickness of 0.125 wavelength. In this case, k 2 has an extremely large value of 28.5% and hence the mode is suitable for a SAW resonator for use in a voltage-controlled oscillator. By means of this SAW, SAW-VCOs at 400 and 170 MHz for mobile communication are fabricated. At 400 MHz, the frequency variable width is 54 MHz (3.2%/V) and the phase noise is less than 115 dBc/Hz at 25 kHz; the corresponding values at 170 MHz are 24 MHz (3.4%/V) and < 12 dBc/Hz at 25 kHz. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(4): 4958, 2001

Fabrication method for grating‐mode‐type SAW resonator used in voltage‐controlled oscillator: optimum shape for electrode fingers and investigation of accurate process techniques

“…12 shows a chip photograph of a 170-MHz SAW resonator used in the VCO for industrial wireless terminals. Figure 14 shows characteristics of the 170-MHz VCO using the present SAW resonator [13]. Each SAW resonator is sealed in an SMD package with 3.8 mm square (in the right-hand photo) and is extremely small in size as a resonator in this frequency range.…”

“…3, the Al-electrode thickness dependence of each resonant mode of the SAW resonator is plotted [13]. 3, the Al-electrode thickness dependence of each resonant mode of the SAW resonator is plotted [13].…”

“…Therefore, SAW filters for cellular phones, SAW diplexers [13], and timing extraction high-Q filters for optical communication [4] have already been developed. Therefore, SAW filters for cellular phones, SAW diplexers [13], and timing extraction high-Q filters for optical communication [4] have already been developed.…”

Love‐wave‐type/Rayleigh‐wave‐type SAW resonators with thick Al‐grating structure

“…A Love-wave-type SAW propagating on a 15°-rotated Y-cut X-propagation LiNbO 3 substrate exhibits extremely strong piezoelectric characteristic and the Love-wave SAW in a device with Au electrodes is reported to provide a wide variable-oscillation range [3]. A 150-MHz VCO using a Love-wave SAW propagating on a grating formed with thick Al films has been reported to provide both wide variable range of oscillation frequency and high C/N [6], and a Love-wave SAW filter in a device with Cu electrodes has been reported to have an extremely wide bandwidth [7].…”

“…In this paper, the propagation characteristics of the Love-wave SAW and Rayleigh-wave SAW are studied by simulation and experiments. Studies of the suppression of spurious responses caused by degenerate Rayleigh-wave SAW, test fabrication of a SAW resonator for a VCO with spurious responses eliminated, and trial fabrication of a wideband SAW-VCO are reported in this paper [9]. Figure 1 shows the impedance characteristics of a SAW resonator with spurious responses.…”