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
u
_CO
. 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
u
_CO
, i.e.,
VH
<;
u
_CO
. Here, we present a method on how to determine
VH
and the
I
-
V
branch below
u
_CO
, 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.