Characterization and Modeling of Sparkless Discharge to a Touch Screen Display

Although corona discharge to a touchscreen display is not associated with the spark, it could cause soft and hard failures due to electromagnetic coupling to sensitive electronics beneath the glass. Experimental data were obtained to characterize these sparkless discharges and an equivalent circuit model was constructed to predict the resulting coupling to touchscreen electronics. Measurements and simulation indicate that a thinner glass and a higher touchscreen indium-tin-oxide (ITO) sense trace impedance both lead to higher ESD risk by delivering higher energy into the sensing IC. A CST co-simulation model is proposed and is shown to model the displacement current accurately. Charge movement and dissipation on the glass surface is represented using a disk with conductivity proportional to the reciprocal of radial distance. Dust figure measurements were used to study the effects of the glass type, glass thickness and voltage level on the corona discharge and the current coupled to the touchscreen patch on the display. These results can be used to drive full wave co-simulation models which try to anticipate the impact of sparkless discharges on the touchscreen electronics.

I. Introduction

Corona discharge leads to potential risk for soft and hard failures when discharging to the display surface of a mobile device. Although the glass provides insulation from direct sparking to the internal electronics, problems may occur due to electromagnetic coupling [1–3]. Capacitive coupling to the sensing pixel, for example, can cause burnout of the ITO (Indium tin oxide) trace which feeds the sense circuitry.