Adaptive Source Bias for Improved Resistive-Open Defect Coverage during SRAM Testing
Abstract
SRAM testing is becoming more and more challenging due to issues caused by continuous device scaling. Fabricated SRAMs are submitted to random and systematic process variability, which strongly affect the cell's behavior and also the ability of test algorithms to detect faults. Traditionally, bias conditions have been used to improve the behavior of the SRAM under process variations by applying body bias to compensate for the effect of variability. Based on the same principle, bias conditions also affect the cell's behavior when resistive-opens are present, hence affecting test's defect coverage capability. Both body- and source-bias conditions are analyzed in this paper to find the way to improve defect detect ability in the SRAM cell. Source-biasing has been proven to be the more effective of the two, leading to more than 3X improvement of the defect detected value. Also, by adapting the source-bias conditions to process parameter values, over- and under-testing of the SRAM can be avoided.
Keywords
SRAM chips
fault diagnosis
integrated circuit testing
SRAM testing
adaptive source bias
continuous device scaling
fault detection
process variability
resistive-open defect coverage
test algorithms
Circuit faults
MOSFET
SRAM cells
Testing
Threshold voltage
6T SRAM Cell
Adaptive Test
Resistive-open Defects
Source-Biasing