Mask-free femtosecond laser photochemical nanoprinting of hierarchical 3D ZnO toward FET and UV photodetection

Geometric control of zinc oxide on chip/wafer with versatile designs promises tremendously rewarding applications. However, high-complexity structures surpass the capabilities of in-plane coating, sputtering, or hydrothermal synthesis. Here, a digital photochemical synthesis leveraging single-step, maskless femtosecond laser direct writing incorporating a vinylphosphonic acid (VPA) chelating agent was used to grow three-dimensionally structured zinc oxide (ZnO). This strategy allowed multiple optoelectronic functions. Several high-freedom 1D/2D/3D ZnO nanowires, patterns, and out-of-plane structures were all-in-one integrated onto chips. The freestanding ZnO field-effect transistors delivered a saturation field-effect mobility of 4.6 cm² V⁻¹ s⁻¹ , and less than 2% performance degradation after 30 days of ambient storage. The as-fabricated self-powered ultraviolet photodetectors achieved a photoresponsivity of mA W⁻¹ level under 365 nm irradiation, with rise/fall times of 33 s/21 s, a UV/dark ratio exceeding 2.4 × 10⁵, and reliably detected weak UV light as low as 0.12 μW cm⁻². After repeated on-off illumination cycles, the device retained over 98% of its initial photocurrent. The 3D laser-synthesized ZnO channels exhibited high carrier mobility and UV light sensitivity at the microscale, demonstrating great prospects for miniaturized electronics or IoT sensors.