Open Defects in Nanometer Technologies Models, Test and Diagnosis - Models in Hardware Testing - page 8

Fig. 1.6 ( a ) Sum of all the gate leakage currents .I FN / at the floating input of a defective inverter,
( b ) prediction of the steady state voltage ( Arumı et al. 2008b )

I 1 represents the total gate leakage currents flowing from the V DD rail to the floating
node. I 2 is equivalent to the total gate leakage currents flowing from the floating
node to the GND rail and I 3 stands for the total gate leakage currents flowing be-
tween the floating node and the output node of the inverter.
With the knowledge of the gate leakage currents influencing the downstream
gate, the steady state voltage of the floating line can be predicted. Assuming a float-
ing line driving an inverter for a 90 nm technology, Fig. 1.6 a illustrates the total gate
current .I FN / at the input floating node related to the input and output voltages of
the downstream gate (inverter). The pairs (V FN , V OUT ) where the resulting current
is zero are shown in Fig. 1.6 a as a level curve. Thus, as the transfer characteristic
of the downstream gate is not modified, the steady state is determined by the inter-
section point between the (V FN , V OUT ) pairs resulting in I FN D 0 and the transfer
characteristic of the gate, as shown in Fig. 1.6 b . In this case, a logic low (high) level
is generated at the input (output) of the defective inverter.

1.2.1.2 Resistive Open Defects in Interconnect Lines

When open defects cause a finite increment of line resistance, they are called resis-
tive (or weak ) opens. A resistive open weakens the affected signal, which has delay
consequences on the transient behavior of the defective circuit ( Moore et al. 2000 ) .
Two real weak open defects are exemplified in Fig. 1.7 .
The electrical behavior of resistive opens relies on the value of the unknown
resistance. Experimental measurements were carried out by Rodrıguez-Montanes
et al. ( 2002 ) on a set of test structures of a 0:18 m technology in order to determine
the open resistance values. Results showed that a high percentage of open defects
were of full nature, with resistances higher than 1 G, as illustrated in Figs. 1.8 and
1.9 . Nevertheless, a non-negligible amount belonged to the class of weak or resistive
opens, with resistances lower than 10 M.