Measuring Holding Voltage Related to Homogeneous Current Flow in Wide ESD Protection Structures Using Multilevel TLP

Due to the negative-differential-resistance-related instability, the current-density distribution in sufficiently wide devices exhibiting S-shaped I-V characteristics becomes inherently inhomogeneous along the device width. High-current-density on-state (i.e., a current filament) and low-current-density off-state regions are spontaneously formed, leading to the formation of a vertical branch in the I-V curve at a so-called coexistence voltage uCO. In electrostatic discharge (ESD) protection devices (PDs), this vertical I- branch usually determines the lowest voltage point that can be accessed by a conventional transmission line pulser (TLP). However, the real holding point of device VH, which is related to an I-V part with a homogeneous current distribution, lies below uCO, i.e., VH <; uCO. Here, we present a method on how to determine VH and the I-V branch below uCO, which is “hidden” when using a conventional TLP analysis. We use a multilevel TLP system and demonstrate it on a 90-nm technology silicon-controlled rectifier ESD PD. Measurement considerations, which take into account the finite speed of the on-state spreading effect and the self-heating effect, are discussed. Implications relevant for latch-up prevention and for the comparison of experiments with 2-D and 3-D technology computer-aided design simulations are also given.