Abstract
In this study, a 3.5-GHz solidly mounted resonator (SMR) was developed by doping scandium in aluminum nitride to form AlScN as the piezoelectric thin film. Molybdenum (Mo) of 449 nm thickness and silicon dioxide (SiO2) of 371 nm thickness were used as the high and low acoustic impedance films, respectively, which were alternately stacked on a silicon substrate to form a Bragg reflector. Then, an alloy target with atomic ratio of 15% Sc was adopted to deposit the piezoelectric AlScN thin film on the Bragg reflector, using a radio frequency magnetron sputtering system. The characteristics of the c-axis orientation of the AlScN thin films were optimized by adjusting sputtering parameters as sputtering power of 250 W, sputtering pressure of 20 mTorr, nitrogen gas ratio of 20%, and substrate temperature of 300 °C. Finally, a metal top electrode was coated to form a resonator. The X-ray diffraction (XRD) analysis showed that the diffraction peak angles of the AlScN film shifted towards lower angles in each crystal phase, compared to those of AlN film. The energy dispersive X-ray spectrometer (EDX) analysis showed that the percentage of scandium atom in the film is about 4.5%, regardless of the sputtering conditions. The fabricated resonator exhibited a resonance frequency of 3.46 GHz, which was a small deviation from the preset resonance frequency of 3.5 GHz. The insertion loss of −10.92 dB and the electromechanical coupling coefficient of 2.24% were obtained. As compared to the AlN-based device, the AlScN-based resonator exhibited an improved electromechanical coupling coefficient by about two times.
Highlights
With continuous technological advancement, the rapid development of RF microelectromechanical devices is urgently required for manufacturing wireless communication equipment
An alloy target with atomic ratio of of 15% Sc was adopted in this study
The X-ray diffraction (XRD) diffraction peak angles of angles of the AlScN films are shifted towards lower angles in each crystal phase, compared the AlScN films are shifted towards lower angles in each crystal phase, compared to those to those of Aluminum nitride (AlN) films
Summary
The rapid development of RF microelectromechanical devices is urgently required for manufacturing wireless communication equipment. The miniaturization and multi-functionality of the equipment have completely changed the way people communicate. Mobile communication devices used in vehicles and aviation, global positioning system (GPS) and military satellites are all applications of wireless communication. With the advent of fifth-generation mobile communication technology (5G), the frequency spectrum, quality and characteristics of filters are becoming more and more important in 5G or higher frequency bands. There are many types of filters; among them, the acoustic wave filter is of the most concern. The acoustic wave filters can be divided into surface acoustic wave (SAW)
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