Low cost, flexible and biodegradable touch sensor fabricated by solvent-free processing of graphite on cellulose paper

There is a strong demand for flexible user interface technology with a desired size and shape to make real world objects touch-interactive. In this regard, plastic based touch sensors have been widely used on account of their adaptability. However, their fabrication involves eco-unfriendly procedures like lithography or other cleanroom processes which contribute greenhouse gases (GHG) and hence raises the need for exploring alternative green fabrication methods. In this work, we report the fabrication of an inexpensive, flexible, biocompatible, low power and environmentally benign interdigitated capacitive (IDC) touch sensor based on cleanroom-free and solvent-free processing of graphite on paper (GOP). The performance of touchpad with four touch sensor keys was evaluated by integrating it with Arduino UNO development board and it functioned similar to the conventional touchpads which are fabricated by utilizing complex procedures and expensive equipments on plastic substrates. The influence of the number and the overlap length of electrode digits on touch sensor performance was investigated and optimized based on variation in capacitance with the interaction of finger with the touch sensor for better performance and enhanced user experience. The pressure due to strength of the touch and strain induced due to bending and folding of the touch sensor resulted in insignificant variation in capacitance and no change in functionality. This suggests that the flexible and robust GOP based touchpad can be used in diverse applications such as user interface for medical diagnostics, health, environment and security monitoring devices where low cost, eco-friendly, flexible, durable and stable touch control is required. This approach of developing highly advanced, efficient yet biodegradable paper electronics which doesn't involve the use of any toxic, flammable or corrosive gases nor chemicals paves the way for next generation green and sustainable eco-friendly electronics. (C) 2016 Elsevier B.V. All rights reserved.