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Emerging Nitride and Fluorite Ferroelectrics for Configurable cm- and mm-Wave Microwave Acoustic Components
Ferroelectric materials have been widely investigated for creation of configurable microwave components such as resonators, filters, and delay lines. The electrical tailorability of inherent polarization in ferroelectrics enables tuning various electrical, mechanical, and electromechanical properties such as dielectric constant, acoustic wave velocity, and piezoelectric coupling. This facilitates the creation of electrical and electroacoustic components with intrinsically configurable operation such as frequency tunability or switchability. Ultra-high-frequency acoustic resonators and filters with intrinsic tunability and switchability are successfully demonstrated using conventional perovskite ferroelectrics/paraelectrics such as lead-zirconium-titanate (PZT) and barium-strontium-titanate (BST). Perovskite ferroelectrics, however, suffer from substantial limitations that hinder frequency scaling of microwave acoustic components to cm- and mm-wave regimes and prevent their massive integration with CMOS circuits. These include their large dielectric and acoustic losses at higher frequencies, challenging thickness scalability to sub-micrometer, small coercive field, and incompatible growth process with front- and back-end-of-line CMOS manufacturing. The recent discovery of ferroelectricity in CMOS-compatible nitride and fluorite films has augured new classes of configurable microwave acoustic components with extreme frequency scalability as well as potential for monolithic integration with CMOS. This talk introduces these ferroelectric materials, with a focus on scandium-aluminum-nitride (ScAlN) and hafnium-zirconium-oxide (HZO), and presents an overview of their enabling properties for creation of integrated acoustic resonators over cm- and mm-wave frequencies. Further, novel configurable acoustic resonator and filter technologies enabled by integration of ScAlN and HZO on semiconductor platforms will be presented, including periodically-poled ScAlN Lamb and bulk-acoustic-wave resonators, and HZO-on-Si ferroelectric-gate fin resonators and filters.