High speed thermal characterization of ESD protection devices

Electrostatic discharge (ESD) protection devices are critical in preventing static charge from damaging integrated circuit (IC) chips. Due to the high speed nature of the ESD event, however, thermal characteristics have been hard to capture or characterize. We investigated the use of the transient thermoreflectance imaging method to characterize the temperature distribution in a time series of thermal maps with 100 ns resolution. We reviewed the high speed transient thermoreflectance method and then demonstrated practical examples of thermal characterization for an ESD diode, a snapback Grounded-Gate n-type Field Effect Transistor (GGNFET), and a silicon-controlled rectifier (SCR). Unique transient thermal characteristics were identified in microsecond time scale. The initial current flow pattern can be identified before heat is diffused in the whole device. In the GGNFET device, current concentration at the corners of the anode and cathode are identified. In the SCR device, inhomogeneous heating in two fingers was observed with a 300 ns time scale, which is an indication of an unstable current flow in the device.