Memory fault models and testing

Abhilash Kaushal, Freescale
EDN (June 29, 2015)

A different set of fault models and testing techniques is required for memory blocks vs. logic. MBIST algorithms that are used to detect faults inside memory are based upon these fault models. This article discusses different types of memory fault models.

Memory fault models – Single cell faults

Stuck at (SAFs): Stuck at faults in memory is the one in which the logic value of a cell (or line in the sense amplifier or driver) is always 0 or 1.

Left: Write operation state diagram of a good memory cell; Right: State diagram for s-a-0 and s-a-1 memory cell

Transition Faults (TFs): In transition faults a cell fails to make a (0 to 1) transition or a (1 to 0) transition when it is written; up transition fault is denoted as <0w1/0/- > and a down transition fault is denoted as < 1w0/1/- >

State diagram for transition faults

Write destructive faults (WDFs): A non transition write operation in a memory cell causes the cell to flip. There are two types of Write destructive faults:

1) Memory cell in state 0, write 0 on it. Cell becomes 1. Denoted as <0w0/1/->

2) Memory cell in state 1, write 1 on it. Cell becomes 0.Denoted as <1w1/0/->

State diagram for write destructive faults

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