Novel Soft Lithography Technologies for Wearable Light Emitting Diodes and Biosensors

Abstract

Soft electronic devices, in particular healthcare-related ones, have been intensively studied over the past decade due to their unique advantages in biomedical applications over the conventional rigid electronics, including conformal contacts on human skin and high deformability that minimizes unwanted inflammatory responses. To achieve the soft nature in high performance electronics and to apply this technology to wearable biomedical electronics/optoelectronics, several strategies have been employed, such as the designed assembly of high quality nanomaterials, combination of unconventional manufacturing processes with existing microprocessing technologies, new design of individual devices with deformable structures, and disease-specific system-level integration of diverse soft electronics. Here, we describe 3 types of noble soft lithography technologies for the wearable electronic/optoelectronic devices. First, alignment of red-green-blue micro pixels with high resolutions up to 2,460 pixels per inch was developed by intaglio transfer printing. This technique is readily scalable and adaptable for low voltage-driven pixelated white LEDs and ultrathin, wearable electronic tattoos, showing the best electroluminescence performance (14,000 cd m-2 at 7 V) among the wearable light-emitting diodes reported up to date. Second, a thermally controlled transfer printing method that is specially designed for the multiple aligned transfer of patterned graphene is developed. Through this approach, accurate and high-yield transfer printing of patterned graphene onto diverse substances is achieved, allowing a transparent, stretchable, and wearable all-graphene electronic/optoelectronic system to be fabricated. Third, biomimetic miniaturized suction cups are designed for the patient-friendly, dry adhesives of smart medical skin. Both strong van der Waals force and induced negative pressure by the ultrasoft mSCs facilitate tight skin coupling without discomfort or irritations, improve sensitivities of the embedded stretchable electronics for continuous vital sign monitoring, and enable multiple drug reloading without loss of the adhesion.