characterization, modeling, and design of esd protection circuits

108 Chapter 4. Simulation: Calibration and Results
A few changes in the simulation structures were made before the final phase of calibration
began to more accurately model the non-salicided test structures used for snapback and
thermal characterization. Since the lumped source/drain resistance introduced during the
calibration of the drain characteristics was unreasonably large, it was removed from the
simulation model. This simplifies the simulation-structure specification and is justified
because the new, salicide-blocked test structures are at least 2.5 times wider than the
previous structures, which implies much more contact area and thus less contact
resistance, and because the package leads are ultrasonically bonded to the contact pads,
introducing minimal series resistance. Since the new structures make use of a salicide
mask, the simulated source and drain contacts are placed at the same distance from the
gate as in the actual structures, in contrast to the minimal contact spacing used for the fully
salicided structures in the previous subsection. This contact-to-gate spacing varies from
3µm to 8µm on the drain and source sides in the test structures and simulations. The
I device / mA
600
400
200
+
V in
-
50Ω
50Ω
Idevice Vdevice 0
0 3 6 Vsb 9 12 15
V device / volts
1/R sb
Fig. 4.41 I-V points from the transmission-line pulse sweep of a standard
50 ⁄ 0.75µm test structure (equivalent circuit shown inset). The trigger
voltage (Vt1 ), snapback voltage (Vsb ), snapback resistance (Rsb ), and
second-breakdown point (Vt2 , It2 ) can be extracted from the curve.
V t1
V t2 , I t2