Fractional Bandwidth up to 24% and Spurious Free SAW Filters on Bulk 15°YX-LiNbO3 Substrates Using Thickness-Modulated IDT Structures

Abstract

To cope with ubiquitous wireless connectivity and the increased and faster data delivery in 5G communication, surface acoustic wave (SAW) filters are progressively requiring wider bandwidths. Conventional bulk 15°YX-LiNbO3 substrates with a large coupling coefficient (K2) are attractive for the low-cost mass production of wideband SAW filters, but these generally suffer from spurious responses, limiting their practical application. In this work, a novel and simple SAW configuration is proposed that uses thickness-modulated interdigital transducer (IDT) structures to overcome the limitations set by spurious responses. Different from the conventional design where the thicknesses of the IDT electrodes in the series and parallel resonators generally kept the same, the proposed configuration adopts IDT electrodes of different thicknesses in the series and shunt resonators to suppress or remove unwanted spurious Rayleigh modes from the filter passband. Two different ultra-wideband SAW filter designs employing thickness-modulated IDTs were designed and fabricated to validate the effective suppression of spurious modes. The SAW filters experimentally featured spurious-free responses in the passband as well as a large 3 dB fractional bandwidth (FBW) in the 18.0% and 24.1% ranges and low insertion losses below 1 dB. This work can significantly broaden the range of applications for SAW devices and can open a pathway to commercialize ultra-wideband SAW filters in 5G communication systems.

Development and Validation of an ANN-Based Approach for Temperature-Dependent Equivalent Circuit Modeling of SAW Resonators

“…Surface acoustic wave (SAW) resonators are devices that utilize the properties of piezoelectric materials to convert mechanical vibrations on a solid surface into electrical signals, and vice versa. Due to their high performance and reliability, these devices are widely used in wireless communication systems for the implementation of filters and oscillators [ 1 , 2 , 3 ]. In recent years, SAW technology has gained significant attention in the scientific community as a highly researched topic, due to its outstanding potential for emerging applications in various fields.…”

“…These early SAW devices were primarily based on quartz crystal substrates and were utilized in radio communication systems and other high-frequency electronic devices. Over the years, SAW technology has undergone a significant evolution, with the development of new materials and fabrication techniques [ 1 , 2 , 6 , 7 , 8 ]. This has led to the creation of SAW devices with improved performance, increased functionality, and expanded application.…”

Partially Etched Piezoelectric Film Filled with SiO2 Structure Applied to A1 Mode Resonators for Transverse Modes Suppression

“…Acoustic resonators are one of the most indispensable components of radio-frequency (RF) front-ends used in mobile communications due to their low cost, small size and design flexibility [ 1 , 2 , 3 , 4 , 5 ]. With the arrival of Fifth Generation (5G) mobile communication, traditional acoustic resonators, mainly surface acoustic wave (SAW) and bulk acoustic wave (BAW) resonators, face higher technical challenges.…”