Fraunhofer Institute for Electron Beam
In the project, novel high-frequency filters and electro-optical converters are being developed together with the project partners from Carnegie Mellon University (CMU). These are based on piezoelectric and ferroelectric aluminum scandium nitride layers that are deposited at Fraunhofer FEP.
The basis for the targeted devices is the development of an industrially suitable, stable and reproducible deposition technology for piezoelectric AlScN layers with good thickness and composition homogeneity over 150 and 200 mm wafer diameters at high deposition rates of 3 nm/sec. An effective piezoelectric coefficient d33,f of 12 pm/V was measured on AlScN films deposited by reactive magnetron sputtering of sputtering target from an AlSc alloy with 35% Sc content. Ferroelectric polarization was possible at electric field strengths of ±3.8 MV/cm.
In the field of mobile communication, increasingly large data volumes require the transition to ever higher transmission frequencies. This requires new concepts for components such as frequency filters. One example is the so-called Overmoded Bulk Acoustic Resonator developed in the project. The design of these resonators for frequencies of 50 GHz was carried out at the partner CMU, the layer deposition of the piezoelectrically active layer and the acoustic resonator at FEP. Processing into a device and characterization was again carried out at CMU1.
A kt² value of 5.5% and a Q value of 108 were measured. With these parameters, the application in future components is already foreseeable.
Photonic components are currently mainly based on lithium niobate due to its advantageous electro-optical properties. However, this material is not compatible with other semiconductor manufacturing processes. The aim is to produce equivalent components based on AlScN, which is CMOS-compatible and thus enables the integration of photonic components into microelectronic circuits. A first step in this direction was the production and characterization of AlScN waveguides. It was shown that the optical losses are low (five times lower than the state of the art ), so that optical components based on AlScN waveguides can be realized. Furthermore, a first functional electro-optical modulator based on AlScN has already been demonstrated.
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1 J. Baek, S. Barth, T. Schreiber, H. Bartzsch, G. Piazza: 52 GHz 35% Scandium Doped Aluminum Nitride Overmoded Bulk Acoustic Resonator, 2024 Ultrasonics, Ferroelectrics, and Frequency Control Joint Symposium
2 B. Friedman, S. Barth, T. Schreiber, H. Bartzsch, J. Bain, G. Piazza: Measured optical losses of Sc doped AlN waveguides, Vol. 32, No. 4 / 12 Feb 2024 / Optics Express 5252