| Abstract [eng] |
Flexible electronics technology is already being utilized in industrial and medical devices by worldwide users. This new generation of electronics assists in monitoring the vital signs of premature babies and athlete's hydration. Another application of this technology is in robotics, where flexible sensors enable robots to mimic the touch of living organisms. However, whether intended for humans or robots, these devices present a significant chemical and engineering challenge. This is due to electronic components typically being delicate and rigid. One of the earliest milestones in flexible electronics was achieved by the team led by at the University of Tokyo. They reported the development of flexible electronics, covering an area of 65 cm$^2$, which could be used as robot skin. This material was composed of polyimide plastic layers. While this engineering breakthrough is fascinating, certain applications require higher carrier mobilities and physical properties that do not degrade under harsh environmental conditions. Consequently, inorganic optoelectronics emerges as a superior alternative. Using inorganics for flexible electronics presents numerous challenges associated with significant mechanical mismatch between bulk inorganic semiconductors and flexible substrates. One solution is to produce thin layers, as thinner films are more flexible, given that the critical bending radius is smaller for thin films than for bulk materials. Various fabrication strategies for thin inorganic films include epitaxial lift-off techniques using a chemically etched sacrificial layer, optically induced separation between the epilayer and substrate, brute-force mechanical spalling using a metal stressor layer, and two-dimensional (2D) material-assisted layer transfer with a metal stressor. These thin layers afterward can be transferred onto flexible substrates. In this study, the 2D material-assisted lift-off of thin gallium nitride (GaN) layers was studied. The 2D material acted as an interlayer between the substrate and the growing GaN, restricting strong bonding formation and facilitating subsequent layer exfoliation. Moreover, high crystal quality material can be grown with remote and pin-hole-assisted regimes, where the substrate underneath the 2D material modulates the growing structures. Previous research has demonstrated the benefit of this technique for vertically stacked full-color micro-LEDs. Additionally, this approach holds promise for applications in robotics, as GaN and its alloys exhibit strongly pronounced piezoelectric properties, which are advantageous for creating long-lasting robotic skins for precise stress measurements. Thus, the objective of this study was to exfoliate GaN layers from graphene, which would serve as a platform for the formation of flexible membranes composed of group III nitrides. |
