Open Defects in Nanometer Technologies Models, Test and Diagnosis - Models in Hardware Testing - page 17

et al. ( 1999 ) carried out simulations with a 0:25 m technology to find the critical
resistance. Results showed that, for interconnect opens, most critical resistances
were about a few M.
Another issue to be addressed is that the resistive line acts as a low pass filter.
Assuming that R o >> R ON , the time constant depends mainly on the open resistance
.R o / and location (parasitic capacitances located after the open). If the time constant
due to the defect is lower than the signal period, the defective node reaches its fi-
nal state before the next clock period is generated. However, if the time constant is
higher than the signal period, the defective node has not reached the final state yet
when the next transition has already been initiated. Hence, for every clock cycle,
the defective node does not start from the expected logic 0 or 1 value but from some
intermediate state. This effect is the so-called history (or memory) effect ( Renovell
et al. 2006 ; Arumı et al. 2008a ) . In Fig. 1.17 , the evolution of the defective line
.V def / driven by an inverter is shown. An input sequence where 70% of values are
logic 1s is considered. When starting from 0 V, the value of V def increases until it
evolves close to the region of 70% of V DD . Therefore, for the next cycle, the initial
voltage is at an intermediate value instead of the expected 0 or V DD . Experimental
results revealed the impact of this phenomenon. The experiment consisted of ap-
plying a rising transition at the defective node and measuring the propagation delay
between the input and the output of the inverters for different initialization states
and resistances (see Fig. 1.18 ) . This initialization involved sequences of 0s and 1s
being applied to the defective node from 0% to 100% of 1s prior to triggering the
transition. The results are listed in Table 1.3 , where 'd' denotes the defect detection
and ' ' denotes a test escape. The results show that the detectability interval of open
resistances decreases as the initial state is closer to the final state (logic 1 for a rising
transition).

1

0.8

0.6

input
V_def

0.4

0.2

Fig. 1.17 Dynamic behavior
of the defective line ( Arumı
et al. 2008a )

0

0 2 4 6 8 10

Ti m e (µ s)

Fig. 1.18 Experiment
performed to show the
history effect

R o