AlxGa1-xN nanomembranes enabled by two-step nanoporous-assisted controlled spalling for flexible piezoelectric sensors

Here, we demonstrated the fabrication of GaN, AlGaN, and AlN nanomembranes through a two-step nanoporous (NP)-assisted controlled spalling technique and utilized these nanomembranes to create flexible piezoelectric sensors. In this process, the first NP served as a seeding layer for overgrowing the planarized Al x Ga 1-x N layers, while the second NP acted as a separation layer. We conveniently peeled off the overgrown thin film nanomembranes at the interface of the second NP using a Ni stressor and thermal release tape. The crystal quality of the nanomembranes was confirmed through various characterizations, including electron microscopy, X-ray diffraction, and Raman spectroscopy. The inherent flexibility of the nanomembranes provided an opportunity to fabricate highly responsive piezoelectric sensors. The resulting flexible GaN and AlN membrane-based sensors exhibited exceptional sensitivity to pressure and bending-induced strain. Moreover, these devices easily detected human motion and airflow. The NP-assisted controlled spalling process is a controllable and scalable mechanical lift-off technique that opens up numerous possibilities for the development of innovative device applications. • Thin GaN buffer layer was adopted to grow additional GaN, AlGaN, AlN thin-film on nanoporous structure. • Al x Ga 1-x N nanomembranes were demonstrated through two-step nanoporous-assisted controlled spalling. • Flexible piezoelectric sensors were fabricated based on the nanomembranes. • The piezoelectric sensors were tested by using bending, finger tapping, finger bending, and air flow.