Columbia University

Technology Ventures

Diagnosis of NBTI degradation in SRAM register files at operating temperatures

Technology #cu15138

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Mingoo Seok
Managed By
Greg Maskel
Patent Protection
US Patent 9,424,952

A major source of degradation in static random-access memory (SRAM) register files is negative-bias temperature instability (NBTI) degradation of their PMOS devices. Measurement and repair of this aging degradation is useful in ensuring long-term quality and reliability of performance in SRAM register files. This technology is a sensor which detects the threshold voltage across a range of temperatures and voltages to test NBTI degradation in SRAM register files during in-field operation. By measuring the threshold voltage over time, NBTI degradation can reliably be determined under operating conditions, and recovery vectors for PMOS performance can be determined based on the sensor readings. This ability to perform both in situ and in-field sensing of NBTI degradation to SRAM register files can be a critical component for dynamic reliability management.

In-field NBTI degradation sensing can track reliability of SRAM register files as well as generate recovery vectors for preserving performance

Measurement and repair of NBTI degradation is important to ensure the long-term stability of the SRAM register files, but current in situ methods cannot be used under variable temperatures during device operation. This technology allows for testing of threshold voltages of the device’s transistors under such conditions, particularly temperatures and operating voltages where existing techniques have significant error in determining degradation. Additionally, these values can be used to correct voltage differences between cells. The ability to sense NBTI degradation during device operation has the potential to improve the efficiency of quality checks in PMOS systems and allow for correction of SRAM register files in a timely manner.

A prototype of the technology has been tested on a fabricated 32 × 32b 6T-SRAM register file in the 65 nm standard. The prototype was able to detect degradation at a much lower error rate across a 60-degree Celsius temperature range and a 0.6-0.9 voltage variation than conventional techniques.

Lead Inventor:

Mingoo Seok, Ph.D.


  • Regular sensing of threshold voltage to determine the presence of NBTI degradation of SRAM devices
  • Differentiating the threshold voltage difference between two PMOSs
  • Creating recovery vectors for degraded devices
  • In-situ, in-field quality testing while the SRAM device is being used


  • Reliably NBTI degradation in-situ and in-field
  • Can generate recovery vectors to fix a strength skew between to bitcells
  • Works across a range of temperatures and voltages
  • Can be implemented by reconfiguring 6T SRAM bitcells

Patent Information:

Patent Pending: (US 20160358672)

Tech Ventures Reference: IR CU15138

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