Piezoelectric Microacoustic Metamaterial Filters

Area of Science:

• Acoustic metamaterials
• Microacoustics
• Radio frequency (RF) devices

Background:

• Traditional microacoustic filters rely on coupled acoustic resonances, requiring precise, high-resolution trimming for frequency tuning.
• Existing methods often involve complex fabrication steps like mass-loading or fine control of layer thickness, especially for GHz filters.

Purpose of the Study:

• To introduce and characterize the first microacoustic metamaterial filters (MMFs) that utilize acoustic metamaterial structures for bandpass generation.
• To demonstrate an alternative to resonator-based filters, simplifying fabrication and tuning processes.

Main Methods:

• Designed and fabricated MMFs using a 400-nm scandium-doped aluminum nitride (AlScN) film with 30% doping.
• Employed a chain of three acoustic metamaterial (AM) structures: an AM transmission line (AMTL) and two AM reflectors (AMRs).
• Validated performance using finite-element modeling (FEM) simulations and experimental measurements of fabricated devices.

Main Results:

• The fabricated MMFs operate in the RF range, exhibiting filter responses with a center frequency in the ultrahigh-frequency range.
• Achieved a fractional bandwidth (FBW) of approximately 2.54% with a loss of around 4.9 dB.
• Observed an in-band group delay of 70 ± 25 ns and a temperature coefficient of frequency (TCF) of approximately 22.2 ppm/° C.

Conclusions:

• Microacoustic metamaterial filters (MMFs) offer a viable alternative to conventional microacoustic filters by leveraging AM structures.
• MMFs eliminate the need for high-resolution trimming and mass-loading steps, simplifying fabrication.
• These filters demonstrate promising performance for RF applications, with bandwidth determined by AM structure geometry and material properties.