SIEMENS Configurable BISR Chain for Fast Repair Data Loading

Motivation

• Today’s designs may have tens of thousands of memories with repair redundancy
• It takes a long time to load the repair data serially during system power-up
• Can we take advantage of the fact that very few of the memories actually need repair to significantly speed up the process?

Outline

• The general memory repair system
• Prior work
• Configurable BISR chain repair system
• Experimental results
• Conclusions

The general memory repair system

• Dedicated repair register for each memory
• Repair enable indicates that memory needs repair
• Most repair registers contain only contain 0s and allow compression of repair information in fuse box

Prior work (repair sharing)

• Use same repair solution for several memories
• Good results obtained for memories using row repair and memories behind a shared bus
• Limited application for distributed memories using column repair
• Potential yield loss

Prior work (memory bypass)

• Each repair register can be bypassed
• Configuration chain loaded first to select repair registers to include in chain
• Pipeline flop needed to avoid long asynchronous paths
• Speedup limited to about 5X

Configurable BISR chain repair system

• Extend Devanathan’s idea to bypass several repair registers at a time
• Bypassing longer segments reduces the overhead associated to the configuration chain

Segment selection circuit (SSC)

• Structure similar to Segment Insertion Bit (SIB) of IEEE 1687
  • Selects/bypasses associated chain segment
• SSC has additional circuitry to identify segments that need repair
  • 1-detection logic

Active scan path with bypassed segment

• Left segment included in scan path because at least one memory needs repair
• Right segment bypassed because none of the memories need repair
  • Segment input forced to 0

Active scan path (configuration chain selected)

• Active scan path (configuration chain selected)

Repair data programming sequence

Power-up sequence

Partitioning algorithm considerations

• Number of segments depends on a few factors
• Most important one is defect density
  • High defect density requires shorter segments to reduce probability of having to include a segment
• Segments of pre-existing IP blocks must be included as is
  • Not always possible to implement optimal segment size

Calculation of optimal segment size

• The BISR Chain Shifting time T = Nrepair X L/Nseg + 2 X Nseg
  • L: the total length of the repair registers
  • Nseg: number of segments
  • Nrepair : number of segments requiring repair
• To minimize T
  • ( Nrepair X L / Nseg + 2 X Nseg )′ = 0
• : = /2
• = /g

Repair data loading speedup factor (single repair)

Repair data loading speedup factor (two repairs)

Repair data loading cycles

(assumed vs actual number of repairs)

Conclusions

• A configurable BISR chain repair system is proposed to speed up repair data loading during chip power-up
• Experimental results show that number of clock cycles can be reduced by one to two orders of magnitude compared to previous methods

Documents / Resources

SIEMENS Configurable BISR Chain for Fast Repair Data Loading [pdf] User Guide Configurable BISR Chain for Fast Repair Data Loading, Configurable BISR Chain, BISR Chain for Fast Repair Data Loading, BISR Chain, Chain

References

• User Manual