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Modulation of Temperature Coefficient of Frequency of Surface Acoustic Wave Devices by Phase Velocity Dispersion | IEEE Journals & Magazine | IEEE Xplore

Modulation of Temperature Coefficient of Frequency of Surface Acoustic Wave Devices by Phase Velocity Dispersion


Abstract:

The temperature coefficient of phase velocity (TCV) and thermal expansion coefficients (CTE) were usually treated as two major terms of temperature coefficient of frequen...Show More

Abstract:

The temperature coefficient of phase velocity (TCV) and thermal expansion coefficients (CTE) were usually treated as two major terms of temperature coefficient of frequency (TCF). In this work, owing to the dispersion of phase velocity ( {V}_{p} ), a coupling mechanism of TCV and CTE in surface acoustic wave (SAW) resonators based on directly bonded LiTaO3/SiC heterosubstrate was investigated. {V}_{p} of the shear horizontal SAW (SH-SAW) in LiTaO3/SiC exhibited strong dispersion characteristics with the variation in LiTaO3 film thickness ( {h}_{\textit {LT}} ) to interdigital transducer pitch ( \lambda ) ratios ( {h}_{\textit {LT}}/\lambda ). Then, when {h}_{\textit {LT}}/\lambda changed due to thermal expansion, {V}_{p} would change synchronously, indicating a variation in TCV resulted from CTE. Considering this coupling effect, a revised term ( {\text {TCF}}_{\text {d}} ) containing the first deviation of {V}_{p} to {h}_{\textit {LT}}/\lambda as a measure of dispersion was derived and introduced into the conventional TCF formula. Moreover, the negative TCF could be compensated by the coupling term if {\text {TCF}}_{d} is positive. In experiments, the SH-SAW resonators with small {h}_{\textit {LT}}/\lambda (0.085–0.18) exhibited well-compensated TCF values at anti-resonance frequency ( {\text {TCF}}_{a} ). Particularly, the one with {h}_{\textit {LT}}/\lambda of 0.11 exhibited a {\text {TCF}}_{a} of −4.1 ppm/K and an extremely high Q of 8050. The filter with a center frequency of 2.76 GHz showed the TCF values of −8.0 and −15.6 ppm/K at the left and right edges of passbands, respectively. This work extended a more thorough view of mechanism of TCF in heterosubstrate-based SAW resonators and demonstrated the potential to realize near-zero drift SAW devices on heterogeneous substrates with strong dispersive phase velocities.
Published in: IEEE Transactions on Electron Devices ( Volume: 71, Issue: 10, October 2024)
Page(s): 6261 - 6267
Date of Publication: 27 August 2024

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I. Introduction

The ever-increasing demand for the sophisticated signal processing functions on-chip has driven the developments of the radio frequency (RF) acoustic devices [1], [2], [3], [4], [5]. Particularly, the RF front-end architectures for the latest mobile terminal devices must support an increasing number of frequency bands in 5G era, due to the compact spectrums and the narrower frequency band gaps, as schematically shown in Fig. 1. Therefore, RF acoustic filters with low insertion loss, steep skirts, and enhanced temperature stability are highly desirable. To address these requirements, surface acoustic wave (SAW) resonators with ultrahigh quality factor (Q) and stable temperature characteristics are strongly required.

Schematic of a typical RF front-end module, and the diagram of the frequency bands that the mobile terminal devices need to support in 5G era.

References

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