sensors Review Review of Capacitive Touchscreen Technologies: Overview, Research Trends, and Machine Learning Approaches Hyoungsik Nam * , Ki-Hyuk Seol, Junhee Lee, Hyeonseong Cho and Sang Won Jung Department of Information Display, Kyung Hee University, Seoul 02447, Korea;
[email protected] (K.-H.S.);
[email protected] (J.L.);
[email protected] (H.C.);
[email protected] (S.W.J.) * Correspondence:
[email protected]; Tel.: +82-2-961-0925 Abstract: Touchscreens have been studied and developed for a long time to provide user-friendly and intuitive interfaces on displays. This paper describes the touchscreen technologies in four categories of resistive, capacitive, acoustic wave, and optical methods. Then, it addresses the main studies of SNR improvement and stylus support on the capacitive touchscreens that have been widely adopted in most consumer electronics such as smartphones, tablet PCs, and notebook PCs. In addition, the machine learning approaches for capacitive touchscreens are explained in four applications of user identification/authentication, gesture detection, accuracy improvement, and input discrimination. Keywords: touchscreen; capacitive; display; SNR; stylus; machine learning 1. Introduction Human beings collect a lot of information through their eyes, and many displays Citation: Nam, H.; Seol, K.-H.; Lee, around us play a key role to transfer this visual information. Displays have evolved dramat- J.; Cho, H.; Jung, S.W. Review of ically from cathode-ray tube (CRT) [1–4] via plasma display panel (PDP) [5–10] and liquid Capacitive Touchscreen Technologies: crystal display (LCD) [11–15] to cutting-edge organic light-emitting diode (OLED) [16–22] Overview, Research Trends, and and micro-LED technologies [23–28].