Models in Memory Testing - Models in Hardware Testing - page 171

stored in the faulty memory cell, but returns an incorrect output. Four types of

dIRFs exist, defined as IRF . xy / D ˚ <x; w y r y =y= N y> ,wherex; y 2 f 0; 1 g .
4. Dynamic Disturb Coupling Fault ( dCFds ): a write operation followed im-
mediately by a read operation performed on the aggressor cell causes the
victim cell to flip. Eight types of dCFdss exist, defined as dCFds . xyz /

D

˚ <x a y v ; w z r z = y v = > ,wherex; y; z 2 f 0; 1 g .
5. Dynamic Read Disturb Coupling Fault ( dCFrd ): a write operation immediately
followed by a read operation on the victim cell when the aggressor cell is in
a given state changes the logical value stored in the victim, and returns an in-
correct output. Eight types of dynamic dCFrds exist, defined as dCFrd . xyz /

D

˚ <x a y v ; w z r z = z = z > ,wherex; y; z 2 f 0; 1 g .
6. Dynamic Deceptive Read Disturb Coupling Fault ( dCFdr ): a write operation
immediately followed by a read operation on the victim cell when the ag-
gressor cell is in a given state changes the logical value stored in the victim
cell, but returns the expected output. Eight types of dCFdrs exist, defined as

dCFdr . xyz / D ˚ <x a y v ; w z r z = z = z > ,wherex; y; z 2 f 0; 1 g .
7. Dynamic Incorrect Read Disturb Coupling Fault ( dCFir ): a write operation im-
mediately followed by a read operation on the victim cell when the aggressor
cell is in a given state does not affect the logical value stored in the victim
but returns an incorrect output. Eight types of dCFirs, defined as dCFir . xyz /

D

˚ <x a y v ; w z r z = z = z > ,wherex; y; z 2 f 0; 1 g .
It is clear that the set of FFMs defined here addresses a very restricted number of FPs
with respect to the complete fault space. This makes dealing with dynamic faults a
very complex task that can be solved only moving from higher abstraction levels to
lower ones where the knowledge of the physical memory layout and structure, and
of the set of realistic defects can be used to restrict the fault space (see Section 6.6 )

6.4.5 n-Coupling Fault Models

In-coupling faults represent fault models where n different memory cells are in-
volved in the fault mechanism (f -cells D n). They are usually referred to as
pattern sensitive faults . In general the content of a cell i (or the ability of i to change
its state) is influenced by the contents of all other memory cells, or by the opera-
tions performed on them. A pattern sensitive fault is the most general definition of
n-coupling fault in which n is equal to the size of the memory.
In a more realistic situation, the so called neighborhood pattern sensitive faults
(NPSFs) are usually considered, in which a reduced set of cells spatially located in
adjacent positions are responsible for the fault mechanism. The neighborhood is the
total number of cells in this set. Traditionally the victim cell is called in this context
base cell , while the aggressor cells are called the deleted neighborhood .
In the PSF the neighborhood can be anywhere in the memory while in the NPSF
the neighborhood must be in a single position surrounding the base cell. These type