LAYERS 9 – Polarization Control for Next Generation Wireless RF Filters
The next generation of wireless communication is expected to push operating frequencies and bandwidths well beyond current standards. In this context, the RF frontend module plays a critical role, with acoustic RF filters representing one of the most challenging elements to scale for higher frequencies. Traditional piezoelectric layer designs reach their limits as resonance frequencies increase, making new approaches to frequency scaling essential.
Periodically poled piezoelectric AlScN layers, also known as P3F structures, offer a promising solution. By alternating the polarization direction within the piezoelectric film, higher order acoustic modes can be excited without reducing the overall film thickness. This enables resonators to operate at significantly higher frequencies, reaching up to the 17 to 18 GHz range, while maintaining quality factors and coupling coefficients required for high performance RF filters.
Evatec has now demonstrated precise polarization control of AlN and AlScN thin films on its CLUSTERLINE® 200 platform. This achievement is particularly significant because the polarization switching is performed in situ during deposition without breaking vacuum and without transferring wafers between tools. Compared to integration based approaches, this reduces process complexity and lowers overall manufacturing costs.
The polarization state of the deposited films was verified using two complementary methods. KOH wet etching was used to confirm polarity dependent etch behavior of AlN layers, while piezoelectric force microscopy enabled direct visualization of piezoelectric domains and their orientation. In addition to single piezoelectric layers, double layer stacks with alternating polarization were successfully grown, with device testing currently in progress.
With many years of experience in AlN and AlScN based piezoelectric thin films, Evatec continues to expand its process capabilities to support future wireless technologies. Polarization controlled AlScN layers represent an important building block for scalable high frequency RF filters required in next generation wireless communication systems.
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