Semiconductor Memory Cell Compensation for NBTI and PBTI Drift
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Solution Overview
Problem
Semiconductor memory devices suffer from negative bias temperature instability (NBTI) and positive bias temperature instability (PBTI), leading to variations in threshold voltage and performance degradation, which can result in data loss or distortion.
Innovation Solution
A semiconductor memory device and method that include an address manager to identify vulnerable cells and a compensation controller to apply specific voltages to manage and compensate for NBTI and PBTI, adjusting threshold voltages of vulnerable cells through NBTI and PBTI compensation operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If normal turn-off voltage is applied to cell transistors, then device operation is maintained, but threshold voltage decreases due to NBTI in vulnerable cells
Solution Approach 1:
The patent applies preliminary compensation actions by identifying NBTI vulnerable cells in advance through address manager and applying compensation turn-on voltages before the threshold voltage degradation becomes critical. This proactive approach prevents data loss by restoring threshold voltages before they reach failure levels.
Solution Approach 2:
The patent changes the voltage parameter by applying compensation turn-on voltages (higher than normal turn-on voltage) to NBTI vulnerable cells and compensation turn-off voltages (lower than normal turn-off voltage) to PBTI vulnerable cells. This parameter adjustment counteracts the threshold voltage shifts caused by NBTI and PBTI effects.
2Reliability
If normal turn-on voltage is applied to cell transistors, then device operation is maintained, but threshold voltage increases due to PBTI in vulnerable cells
Solution Approach 1:
The patent identifies PBTI vulnerable cells in advance through the address manager and applies compensation turn-off voltages before the threshold voltage increase becomes critical. This preliminary action prevents data distortion by restoring threshold voltages before they reach failure levels.
Solution Approach 2:
The patent changes the voltage parameter by applying compensation turn-off voltages (lower than normal turn-off voltage) to PBTI vulnerable cells. This parameter adjustment counteracts the threshold voltage increases caused by PBTI effects.
3Manufacturing precision
If compensation operations are performed for NBTI and PBTI, then threshold voltage stability is improved, but device complexity increases
Solution Approach 1:
The patent segments the memory device into NBTI vulnerable cells and PBTI vulnerable cells using the address manager. This segmentation allows targeted compensation operations on specific cell groups rather than all cells, reducing the overall control complexity while maintaining effectiveness.
Solution Approach 2:
The compensation controller performs multiple functions: it manages both NBTI compensation (applying turn-on voltages) and PBTI compensation (applying turn-off voltages), and it also performs normal read/write operations. This multi-functionality reduces the need for separate dedicated circuits for each function.
Data Source
AI summary
A method of operating a semiconductor memory device includes: providing NBTI information including row addresses of NBTI vulnerable cells among the plurality of memory cells such that a decrease in a threshold voltage of the cell transistor due to application of the normal turn-off voltage about the NBTI vulnerable cells is greater than a reference decrease value; providing PBTI information including row addresses of PBTI vulnerable cells among the plurality of memory cells such that an increase in the threshold voltage of the cell transistor due to application of the normal turn-on voltage about the PBTI vulnerable cells is greater than a reference increase value; increase the threshold voltage of the NBTI vulnerable cells by performing an NBTI compensation operation based on the NBTI information; and decrease the threshold voltage of the PBTI vulnerable cells by performing a PBTI compensation operation based on the PBTI information.