Twin-Cell Memory TDDB Detection Circuit
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Solution Overview
Problem
Time-dependent dielectric breakdown (TDDB) shorts in non-volatile memory arrays, particularly in one-time programmable memory (OTPM) systems, lead to wordline to bitline shorts, causing other cells to be crippled during programming and reading, and existing methods do not effectively detect these failures before they result in data loss and operational stress.
Innovation Solution
A circuit and method that includes a twin-cell memory configuration with a current sense amplifier and an offset current source to detect TDDB failures by skewing the sense amplifier to a known logic state and reading its output with wordlines turned off, allowing for the identification of TDDB failures and subsequent masking of affected cells to prevent further stress during programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high wordline voltage and high source line voltage are applied for programming operations, then programming speed and threshold voltage shift are improved, but time dependent dielectric breakdown (TDDB) shorts occur more frequently
Solution Approach 1:
The patent applies preliminary action by performing a bitline leakage test before completing the programming operation. The test detects TDDB shorts during the programming process, allowing the system to identify and mask defective cells before they cause further issues. This preliminary detection prevents the harmful effects of TDDB shorts while maintaining the high voltage programming benefits.
2Reliability
If bitline leakage test is performed during each write-verify cycle, then TDDB failures are detected earlier, but programming time and operational cycles increase
Solution Approach 1:
The patent merges the bitline leakage test with the existing write-verify cycle by performing the leakage test during the same operational sequence. The test shares circuit resources and timing with the programming operation, allowing TDDB detection without requiring separate dedicated test cycles. This integration minimizes additional time overhead while maintaining reliable defect detection.
3Reliability
If TDDB shorts are detected and cells are masked, then further stress on affected cells is prevented, but device complexity increases due to additional detection circuitry
Solution Approach 1:
The patent applies self-service by using the existing bitline and sense amplifier circuitry to perform the TDDB leakage test. The same hardware components used for normal programming operations are repurposed for defect detection, eliminating the need for separate dedicated test circuitry. This approach prevents TDDB-related failures while avoiding significant increases in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively detects TDDB failures and prevents further stress on affected cells, ensuring optimal programming conditions for other cells by masking cells with TDDB shorts, thereby maintaining the integrity and longevity of the OTPM array.
Implementation Method 1
a current sense amplifier which is connected to the twin-cell memory and is configured to sense a current differential and latch a differential voltage based on the current differential
Data Source
AI summary
The present disclosure relates to a structure which includes a twin-cell memory which is configured to program a plurality of write operations, a current sense amplifier which is connected to the twin-cell memory and is configured to sense a current differential and latch a differential voltage based on the current differential, and at least one current source which is connected to the current sense amplifier and is configured to add an offset current to the current sense amplifier to create the differential voltage.