Models in Memory Testing - Models in Hardware Testing - page 170

Non-transition coupling fault ( CF nt ): a non-transition write operation performed
on the aggressor cell forces the victim cell in a given state: CF nt .xy; w x / D

f <x a y v ; w x = y v = > g ,wherex; y 2 f 0; 1 g .
Nevertheless, all these FFMs are either subsets of the seven FFMs presented before
or can be expressed as a combination of these basic FFMs.

6.4.4 Dynamic Fault Models

As operations are added to the SOS we enter into the dynamic fault space that re-
sults in a theoretically infinite number of potential FFMs. Equation 6.7 describes a
relation between the number of possible FPs and the number m of operations in SOS
for single-cell dynamic faults ( Al-Ars 2005 ) :

( 2m D 0
10 3 m1

# FP singlecell D (6.7)

m 1

The equation clearly shows an exponential relation between the number of FPs and
the number of operations in SOS . This actually reduces the ability of exploring this
huge space of faults for defining FFMs, due to limited availability of simulation time
and computation power.
In order to cope with this problem, experiments on an extensive set of memory
devices showed that the probability of dynamic fault decreases when m increases
( Al-Ars et al. 2002 ). Based on this assumption, two-operations dynamic faults have
been the most studied in the literature and will be considered in this chapter. As
for static fault models, two-operations dynamic faults can be additionally clustered
according to the number of f-cells . j f j / involved in the fault. We shall focus on:
(i) single-cell two-operations dynamic faults . j f j D 1; m D 2/, and (ii) 2-coupling
two-operations dynamic faults . j f j D 2; m D 2/. This leads to a space of 30 single-
cell FPs, plus 192 2-coupling FPs.
This space is in some way already too huge to be explored. For this reason in
Van de Goor et al. ( 2000 ), a limited set of these FPs has been simulated on realistic
defective memory devices and the following established FFMs have been defined:

1. Dynamic Read Disturb Fault (dRDF) : a write operation immediately followed
by a read operation on the same cell changes the logical value stored in the faulty
memory cell and returns an incorrect output. Four types of dRDFs exist, defined

as dRDF . xy / D ˚ <x; w y r y = y= N y> ,wherex; y 2 f 0; 1 g .
2. Dynamic Deceptive Read Disturb Fault (dDRDF) : a write operation immediately
followed by a read operation on the same cell changes the logical value stored in
the faulty memory cell, but returns the expected output. Four types of dDRDFs

exist, defined as dDRDF . xy / D ˚ <x; w y r y = y=y > ,wherex; y 2 f 0; 1 g .
3. Dynamic Incorrect Read Disturb Fault (dIRF) : a write operation immediately
followed by a read operation on the same cell does not change the logical value