Testing Static and Dynamic Faults in Random Access Memories

1
Testing Static and Dynamic Faults in Random
Access Memories

• Lab for Reliable Computing
• Dept. Electrical Engineering
• National Tsing Hua University

2
Reference

• March SSA Test for All Static Simple RAM Faults
• Said Hamdioui, Ad J. van de Goor, Mike Rodgers
  (MTDT02)
• Testing Static and Dynamic Faults in Random
  Access Memories
• Said Hamdioui, Zaid Al-Ars, Ad J. van de Goor
  (VTS02)

3
Outline

• Introduction
• Memory faults classification
• Fault primitives
• March algorithm
• March SS and experiment result
• March RAW and experiment result
• Conclusion

4
Introduction

• Memory testing will become a major cost factor in
  the production of modern VLSIs.
• In order to keep test cost and time limits,
  precise fault modeling and efficient test design
  is essential
• The quality of used tests, in terms of their
  fault coverage and test length, is strongly
  dependent on the used fault models.

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Static versus Dynamic Faults

• OThe number of different operation performed
  sequentially in S.
• Static faults Olt1
• Ex transition fault, need a write to sensitize
  
• Dynamic faults Ogt1
• Ex dRDF00, need w0r0 to sensitize the fault

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Simple versus Linked Faults

• Simple faults
• The faults which cannot be influenced by another
  fault.
• Masking cant occur.
• Linked faults
• The faults that do influence the behavior to each
  other.
• Masking can occur.

C1 C2
C1 C3? C2 C3?
C3(fault frree)
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Classification

• We will focus on static and dynamic simple faults
• Target on one-cell and two-cell fault

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Fault Primitives(1/2)

• Two basic ingredients of any fault models
• (a)A list of performed memory operations
• (b)A list of corresponding deviations in the
  observed behavior from the expected one
• Fault Primitive(FP) -- ltS/F/Rgt
• S Sensitizing operation sequence
• F Fault behavior
• R The logic level of read operation

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Fault Primitives(2/2)

• Single cell ltS/F/Rgt
• S 0 1 0w0, 1w1 0w1, 1w0 r0 r1
• F 0 1 ??
• R 0 1--
• Two cell ltSaSv/F/Rgt
• Sa(Sv) are the sensitizing sequences performed on
  the aggressor(victim) cell
• If Sa is an operation, then Sv should be a state,
  and vice versa

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Static Single-Cell FFMs

• State fault (SF)
• lt 1/0/--gt , lt0/1/--gt
• Transition fault (TF)
• lt0w1/0/--gt , lt1w0/1/--gt
• Write disturb fault (WDF)
• lt0w0/ ?/--gt , lt1w1/ ?/-- gt
• Read destructive fault (RDF)
• ltr0/ ?/1gt , ltr1/ ?/0 gt
• Deceptive read destructive fault (DRDF)
• ltr0/ ?/0gt , ltr1/ ?/1 gt
• Incorrect read fault (IRF)
• ltr0/0/1gt , ltr1/1/0gt

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Static Two-Cell FFMs(1/2)

• State coupling fault (CFst)
• Disturb coupling fault (CFds)
• Transition coupling fault (CFtr)

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Static Two-Cell FFMs(2/2)

• Write destructive coupling fault (CFwd)
• Read destructive coupling fault (CFrd)
• Deceptive read destructive coupling fault (CFdrd)
• Incorrect read coupling fault (CFir)

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• SF can be caused by a short between the node of
  the cell and Vcc and Vss
• TF can be caused by a broken pass transistor
  connection to the bit line (partial open)
• WDF can be caused by a broken bit line

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March SS for Single-Cell FFMs

• SFs,RDFs ltr0/ ?/1gt ,IRFs ltr0/0/1gt by read
• TFs lt0w1/0/--gt by M1,5(M3,5)/M2,1(M4,1)
• WDFs lt0w0/ ?/--gt by read after a non-transition
  write
• DRDFs ltr0/ ?/0gt by two successive read

March SS
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March SS for Two-Cell FFMs

• CFwds lt00w0/?/--gt detected by non-transition
  write and thereafter a read
• CFdrds lt00r0/?/0gt, CFrds lt00w0/?/1gt, CFirs
  lt0r0/0/1gt read operation has to be performed
  to each of two cell
• CFtrs lt00w1/0/--gt transition write and
  thereafter a read can detect

March SS
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FC for March SS
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FC for Different March Tests
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Dynamic Single-Cell FFMs

• 18 possible sensitizing operation xWyWz, RxRx,
  RxWy, xWyRy, where x,y,z0,1
• Only sxWyRy will be considered cause dynamic
  faults
• List of dynamic single-cell FFMs

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Dynamic Two-Cell FFMs

• Four types of S can be distinguished
• Saa ,Svv ,Sav ,Sva
• Only Saa and Svv will be considered and Sxwyry
  will be used
• Faults caused by Saa dCFds
• Faults caused by Svv dCFrd, dCFdrd, dCFir

20
List of Two-Cell Dynamic FFMs
21
Dynamic Faults

• Fault analysis based on defect injection and
  SPICE simulation
• 10?ltRoplt10M ?

22
Analysis Result

23
FC for Different March Test
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Test for Dynamic Single-Cell FFMs
March RAW1 13n
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Test for Dynamic Two-Cell FFMs

• The test coverage is not limited to two-operation
  dynamic faults, but also detect some dynamic
  faults when Ogt2.

March RAW 26n
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March RAW FC
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Conclusion

• A classification of memory faults has been made,
  and the complete set of simple static faults has
  been presented.
• An analytical approach for establishing fault
  models for dynamic faults has been presented.
• The set of fault models has been introduced and
  the new memory tests have been derived to target
  such specific faults.