Physics / mechanism
Piezoelectricity is the linear electromechanical coupling in non-centrosymmetric crystals: applied mechanical stress generates a surface charge (direct effect); applied voltage induces strain (converse effect). Coupling coefficient k² and electromechanical coupling factor kt are the headline figures—PZT ceramics reach kt ~0.5–0.7, AlN ~0.25, LiNbO₃ ~0.5. Resonant frequency is geometry-controlled (MHz–GHz range for thin films). Key material parameters: piezoelectric coefficient d₃₃ (PZT ~200–600 pC/N; AlN ~5 pC/N), Curie temperature, dielectric loss tanδ. CMOS-compatible deposition of AlN and ScAlN (Sc doping pushes d₃₃ to ~15–20 pC/N) is driving integration into bulk acoustic resonators (BAR/FBAR) and MEMS sensors at foundry scale.
Competitive landscape
ScAlN and KNN are the main challengers to PZT (lead-free regulatory pressure) and baseline AlN. PMN-PT single crystals offer d₃₃ >2000 pC/N but are fragile and expensive—defence/medical niches only. Competing transduction mechanisms: capacitive MEMS (no material deposition, lower coupling), magnetostrictive (high force, slow, niche), optomechanical (ultra-low noise, pre-commercial). In RF filtering, piezoelectric BAW competes with SAW (lower frequency ceiling) and LC/dielectric resonators (bulkier). Foundry landscape: GlobalFoundries, TSMC, X-FAB, and SiTime all run AlN or ScAlN BAW processes.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.