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Fault Coverage Analysis of RAM Test Algorithms Marc Riedel McGill University, Montreal, Canada Janusz Rajski Mentor Graphics, Wilsonville, Oregon.

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Presentation on theme: "Fault Coverage Analysis of RAM Test Algorithms Marc Riedel McGill University, Montreal, Canada Janusz Rajski Mentor Graphics, Wilsonville, Oregon."— Presentation transcript:

1 Fault Coverage Analysis of RAM Test Algorithms Marc Riedel McGill University, Montreal, Canada Janusz Rajski Mentor Graphics, Wilsonville, Oregon

2 RAMFLT Outline n Motivation n Fault Models n Methodology and Complexity n Fault Simulation Results n Conclusions

3 RAMFLT Motivation Coverage Measures Needed Functional Memory Testing n A multitude of fault models and test schemes proposed. n Quality of fault coverage difficult to assess. n To validate new test schemes for: l Embedded memories and BIST designs. l Specialized memory architectures (e.g., multiport, FIFO). n To evaluate and rank existing test algorithms: l Deterministic/regular tests. l Pseudo-random/irregular tests.

4 RAMFLT Functional Cell Array Model Bit-addressable 2-D array of binary storage elements: Operations: read, write-0, write-1.

5 RAMFLT Functional Fault Behavior Sensitized read write Unsensitized Detected 0 / 1 1 / 0 n n Sensitized/desensitized by write operations. n n Detected by read operations.

6 RAMFLT Cell Array Fault Models stuck-at, transition, stuck-open, data-retention Coupling Bridging Neighborhood Pattern Sensitive Single Cell idempotent, inversion, state, dynamic (2-cell and 3-cell versions) AND-type, OR-type (2-cell and 3-cell versions) active, passive, static (type I and type II neighborhoods)

7 RAMFLT Fault models are specified as inputs, not hard-coded. Fault Model Specification sensitization desensitization Format Example sensitized fault mem. pattern write op. 1 0

8 RAMFLT Ex.: 2-cell OR-type Bridging Fault sensitization desensitization write-1, a Operation write-1, b write-0, b write-0, a write-0, b write-1, b write-1, a a ab read to either cell returns OR(a,b) b

9 RAMFLT Coverage Analysis case: write Determine which faults are sensitized or desensitized. case: read Classify all sensitized faults as covered. write-1,. read, write-0, write-1, read,.. Simulation performed for arbitrary test sequences.

10 RAMFLT Sensitization & Desensitization active NPSF y y y y Example A write operation can sensitize/desensitize several faults. 3 x p p p p transition in nbh. pattern p, p, p, p sensitizes fault faults in cells y, y, y, y sensitized by write operation

11 RAMFLT Delayed State Transitions Sensitization/desensitization occur after a time delay t D. Used to model retention faults, e.g., "sleeping-sickness" failures in DRAMS: t D

12 RAMFLT Multiple Faults Error masking Multiple sensitizations CFid( y and z CFid( x and y xyz 1 0 xyz CFid( y and z CFid( x and z 1 00 xyz 0 1 1

13 RAMFLT Multiple Faults (cont.) Example n Sensitized faults change the memory pattern. n This affects the sequence of sensitization/desensitization of other faults A B 1 C A B 1 C A B 1 C A B 1 0 C no faults sensitized fault A sensitized faults A and B sensitized fault B sensitized the pattern surrounding cell C is all 1s a sleeping-sickness fault is sensitized

14 RAMFLT Complexity with respect to the test sequence length t with respect to the neighborhood size k with respect to the memory size n & number of coupled cells k NPSFs k-cell coupling faults NPSFs: cells in physical proximity. Coupling faults: cells located anywhere in memory array.

15 RAMFLT Examples of Test Algorithms GALPAT March X March C-

16 RAMFLT 256-bit memory (16 rows x 16 columns) Static Passive Type II NPSF Fault ClassFC (%) Active Static Passive Type I NPSF Active Simulation Results for March X ABF SCF local 3-cell Fault ClassFC (%) CFid ABF SCF global 2-cell CFid 100

17 RAMFLT 256-bit memory (16 rows x 16 columns) Static Passive Type II NPSF Fault ClassFC (%) Active Static Passive Type I NPSF Active ABF SCF local 3-cell Fault ClassFC (%) CFid ABF SCF global 2-cell 100 CFid 100 Simulation Results for March C-

18 RAMFLT Simulation Results for GALPAT 256-bit memory (16 rows x 16 columns) ABF SCF local 3-cell Fault ClassFC (%) CFid ABF SCF global 2-cell CFid Static Passive Type II NPSF Fault ClassFC (%) Active Static Passive Type I NPSF Active

19 RAMFLT Trace of Simulation for ANPSF Test (local)

20 RAMFLT Conclusions n General RAM fault simulation methodology. n Library of over 25 functional fault models. n Coverage statistics for over 40 test algorithms. n Evaluation of arithmetic BIST schemes for memories. Application:


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