An 11.7-GHz ScAlN FBAR Filter: Case Study on Scaling Limits and Challenges

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Abstract
This paper reports an 11.7-GHz compact 50- $\Omega $ ladder filter based on single-layer Scandium Aluminum Nitride (ScAlN) film bulk acoustic resonators (FBARs) with platinum (Pt) electrodes, and uses it as a quantitative case study of the limits encountered when directly scaling to higher frequencies. The measured filter achieves a 3-dB fractional bandwidth (FBW) of 4.0% and an out-of-band rejection greater than 23.1 dB, with a minimum insertion loss (IL) of 6.8 dB. We analyze the origin of this performance through a quantitative framework: (i) a loss decomposition study, (ii) frequency-shift sensitivity that explains the discrepancy between simulated and measured center frequency, (iii) FBW sensitivity to series–shunt separation and port impedance, and (iv) stress-limited aperture that constrains device size. The results establish a realistic, fabric able baseline for directly scaled single-layer ScAlN FBAR filters and outline materials, electrode, and stress-management directions toward lower-loss mmWave acoustic filters.[2025-0162]
Funding Information
  • the Defense Advanced Research Projects Agency (DARPA) COmpact Front-end Filters at the ElEment-level

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