Memory Cell Programming with Pre-Verify Inhibition Control
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Solution Overview
Problem
Existing memory devices face challenges in maintaining narrow threshold voltage distributions of memory cells due to over-programming caused by increasing program pulse magnitude, leading to wider distributions and potential verification errors.
Innovation Solution
A memory device and method that performs a verify operation before applying a fixed program pulse, determining and applying a program inhibition voltage to memory cells based on the verify operation results, thereby maintaining a narrow threshold voltage distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the magnitude of the program pulse is increased to improve threshold voltage distribution, then the threshold voltage can reach the target level faster, but over-programming occurs which results in wider threshold voltage distributions
Solution Approach 1:
A verify operation is performed before applying the program pulse to determine which memory cells need programming. This preliminary verification prevents over-programming by identifying only the memory cells that require threshold voltage adjustment, allowing the program pulse to be applied selectively and accurately.
Solution Approach 2:
The verify operation provides feedback information about the current threshold voltage state of memory cells. Based on this feedback, the control logic determines whether to apply the program pulse and to which specific memory cells, enabling precise control of the threshold voltage distribution without over-programming.
2Productivity
If the number of program loops is increased to achieve target threshold voltage, then more memory cells can be programmed, but the threshold voltage distribution becomes wider due to cumulative programming effects
Solution Approach 1:
Before each program pulse is applied, a verify operation is performed to identify memory cells that have not yet reached the target threshold voltage. This preliminary verification ensures that program pulses are applied only to memory cells that need them, preventing cumulative over-programming effects even across multiple program loops.
Solution Approach 2:
The program operation is divided into multiple program loops, each targeting specific memory cells identified by the verify operation. This segmentation allows the system to handle large numbers of memory cells efficiently while maintaining narrow threshold voltage distributions by treating each cell's programming needs individually based on verification results.
3Speed
If program pulses are applied without verification to improve operation speed, then the programming process is faster, but verification errors occur leading to wider threshold voltage distributions
Solution Approach 1:
A verify operation is performed before applying the program pulse to determine which memory cells require programming. This preliminary verification step, while adding a small time overhead, prevents verification errors by ensuring that program pulses are applied only to memory cells that need them, thereby maintaining both speed and accuracy.
Solution Approach 2:
The verify operation provides real-time feedback on the threshold voltage state of memory cells. This feedback mechanism enables the control logic to make accurate decisions about which memory cells require programming, eliminating verification errors and maintaining narrow threshold voltage distributions while preserving efficient programming speed through targeted pulse application.
Data Source
AI summary
A memory device includes a memory cell array, a peripheral circuit, and control logic. The memory cell array includes a plurality of memory cells coupled to a selected word line. The peripheral circuit performs program operations including a plurality of program loops including a program pulse apply operation that applies fixed program pulses having a constant voltage level and a verify operation. The control logic controls the peripheral circuit to perform a first verify operation included in an N-th program loop among the plurality of program loops before performing a first program pulse apply operation included in the N-th program loop and to apply a program inhibition voltage to memory cells determined, among the plurality of memory cells, based on a result of the first verify operation and target threshold voltages of the plurality of memory cells when the first program pulse apply operation is performed.