A Single Bonding Process for Diverse Organic-Inorganic Integration in IoT Devices

Material hybridization between organic and inorganic materials is crucially important for the development of IoT devices. Especially for wearable and flexible IoT electronics, which are commonly integrated by transfer printing process, organic-inorganic bonding is indispensable for the integration of diverse electronic components. Existing hybrid bonding technologies like laser-assisted bonding or friction stirring welding achieve organic-inorganic bonding using high temperatures as high as melting point of polymers; however, these causes severe material deterioration. Thus, hybrid bonding must be achieved at low temperatures. Here we report a novel hybrid bonding method at the solid-state level and under the atmospheric pressure. Inorganic materials like tin were bonded to polyimide via the ethanol-assisted vacuum ultraviolet (E-VUV) irradiation process, where specimen surface were exposed to a vacuum-ultraviolet (VUV)-irradiated ethanol vapor atmosphere before bonding. VUV-induced re-assembly of ethanol vapor molecules was used to develop hydroxyl-carrying alkyl chains through coordinatively-bonded carboxylate onto tin, whereas numerous hydroxyl-carrying alkyls were created on polyimide. Triggering dehydration via these hydroxyls by merely heating to 150 °C for a few minutes produced robust organic-inorganic reticulated complexes at the tin/polyimide interface. Interface observation via transmission electron microscopy (TEM) shows that the bonded tin/polyimide was extremely compact without readily visible voids. A great number of nano-grains of organic-inorganic complexes were observed in the polyimide side but located ca. 35 nm away from the initial interface, indicating that tin interdiffusion into the polyimide side occurred during hybrid bonding and thus enhanced bondability. The hybrid interface is believed robust due to the strong organic-inorganic nano-grains. Finally, the E-VUV process was experimentally proven to possess broad applicability to diverse inorganic materials, such as aluminum, iron, titanium, and silicon. Adhesion mechanism of E-VUV process was proposed in this study. The E-VUV bonding strategy is expected to be utilized in micro-assembly of flexible and wearable/implantable IoT electronics.