Dust Figure Guided Modeling of Corona Discharge on Touchscreen Surface

Electrostatic discharge to a touchscreen display leads to a corona discharge which creates corona streamers that| propagate along the glass surface. The streamers couple energy to touch sensors underneath the glass which may then cause failure. Modeling the ionized air resistance and the current distribution on the glass surface from corona discharge is challenging. A new methodology is proposed for modeling corona discharge to a touchscreen surface with the help of experimentally measured dust figures. A geometric analysis of the dust figure and how streamer currents couple to the sensor patch matrix is given to explain the modeling method. A SPICE model is proposed to better correlate the ESD gun current with the current coupled to the sensor patches. The ability of the model to predict peak current, charge and rise time is evaluated. Predictions of peak current and charge are within 30% error.

I. Introduction

Electrostatic Discharge (ESD) may cause unintentional disruption of electronic devices. A human handling a portable device can cause an ESD discharge to the touchscreen of the device when touching it with fingertips or metallic items [1]. Because of the high impedance and dielectric breakdown strength of glass, the discharge does not cause a spark but creates an ionized corona which flows across the surface of the screen. As the charge flows across the glass surface, significant energy can be coupled, mainly via displacement current, to the sensors and chips under the screen, which can cause soft and hard failures in the device [2]. Combined with ESD protection models for the IC and system [3], models for the corona discharge to the touchscreen could allow designers to evaluate system-level ESD robustness at the pre- compliance level.