Stepped-Tube Backside Cavity Piezoelectric Ultrasound Transducer Based on Sc_0.2AI_0.8N Thin Films

Area of Science:

• Acoustics
• Microelectromechanical Systems (MEMS)
• Materials Science

Background:

• Conventional piezoelectric micromachined ultrasonic transducers (PMUTs) face limitations in acoustic field angle adjustment due to transducer size constraints.
• Existing methods often require bulky external components like PCBs or horns, hindering miniaturization.

Purpose of the Study:

• To introduce a novel stepped-tube backside cavity PMUT design.
• To optimize acoustic impedance matching and directional characteristics of PMUTs.
• To provide a CMOS-compatible fabrication process for PMUTs.

Main Methods:

• Theoretical simulation and analysis of the stepped-tube backside cavity.
• Fabrication of the proposed PMUT on an eight-inch wafer using CMOS-compatible processes.
• Acoustic comparison experiments to evaluate performance metrics.

Main Results:

• The stepped-tube PMUT demonstrated a 17% increase in average output sound pressure.
• Half-power beam width (θ_-3db) was significantly reduced from 55° to 30° (a 45% decrease).
• Side lobe level signal decreased from 147 mV to 66 mV, indicating improved directivity.

Conclusions:

• The stepped-tube backside cavity design effectively optimizes PMUT acoustic impedance and directional control.
• The CMOS-compatible fabrication ensures stable, cost-effective, and batch production.
• This novel PMUT offers a reliable solution for ranging applications.