Miniaturized high-frequency transparent ultrasound transducers utilizing ambiently tuned ITO electrode

Indium tin oxide (ITO) electrodes are commonly used in transparent ultrasound transducers (TUTs) owing to their superb durability and electro-optical properties. However, the conventional high-temperature ITO deposition process damages the polymer layer and deteriorates the performance of the high-permittivity piezoelectric layer. Here, we propose pressure-tuned radio-frequency (RF) magnetron deposition of ITO electrodes at room temperature. By adjusting the pressure, we improved the crystallinity and controlled crystal orientation. The optimal ITO electrode deposited at 3 mTorr possesses a ratio of (222) orientation to (400) orientation of 1:1 and, at a thickness of ~250 nm, exhibits a sheet resistance of 27.5 Ω/sq with an average transparency of 80.7% (400–1100 nm). The microstructure and sheet resistance (29.9 Ω/ sq) of ITO were maintained when deposited on a high-permittivity piezoelectric layer, lead magnesium niobate–lead titanate (PMN–PT). Compared to a conventional room‑temperature ITO electrode in our process (10 mTorr, ~250‑nm thickness, approximately 100 Ω/sq), our optimized ITO electrode demonstrates significantly improved performance for PMN–PT‑based TUT. Through simulations, we showed that our proposed ITO provides a twofold enhancement in phase velocity and voltage within the ITO transmission line compared to conventional ITO electrodes. Additionally, actual transducer tests confirmed a 4.7 dB improvement in loop sensitivity and a 117.9% increase in bandwidth. Our TUTs enable multimodal imaging, enabling high-quality ultrasound imaging with the potential to make a significant impact in medical diagnostics and the biomedical field.