Auxiliary Memory Cell Selection for Reference Signal Generation
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Solution Overview
Problem
The existing procedures for programming reference cells in non-volatile semiconductor memories are time-consuming and costly due to the need for precise setting of threshold voltage values, which is sensitive to process variations and requires repeated programming sequences.
Innovation Solution
The method involves using a population of auxiliary cells to achieve a statistical distribution of threshold voltages through programming or erasure, allowing for the selection of an auxiliary cell with a threshold voltage close to the target value, which can serve as a reference cell for operations, thereby reducing the time and cost associated with setting reference cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If precise programming sequences are used to set threshold voltage values of reference cells, then manufacturing precision is improved, but productivity deteriorates due to time-consuming repeated programming
Solution Approach 1:
The patent applies preliminary action by pre-programming a population of auxiliary cells with identical programming parameters before selection. This creates a statistical distribution of threshold voltages in advance, allowing the reference cell to be selected rather than programmed during production, thereby resolving the contradiction between precision and productivity
Solution Approach 2:
The patent uses copying by creating multiple copies (auxiliary cells) with the same programming parameters, then selecting one that naturally falls within the desired threshold voltage range due to statistical distribution. This eliminates the need for iterative programming adjustments on each reference cell, improving productivity while maintaining precision through selection from pre-programmed copies
2Manufacturing precision
If repeated programming sequences are performed to achieve accurate threshold voltage, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The invention performs the programming action preliminarily on all auxiliary cells simultaneously with standard parameters, then selects the appropriate cell based on its naturally occurring threshold voltage. This eliminates the need for repeated programming sequences and associated time losses while maintaining the required accuracy through statistical selection
Solution Approach 2:
The auxiliary cells serve themselves by naturally developing different threshold voltages within the programmed population due to statistical variations. The system selects from these self-generated variations rather than forcing each cell to achieve the target voltage through repeated programming, thereby reducing time loss while maintaining precision
Data Source
AI summary
In a semiconductor memory device, a method for obtaining at least one reference cell adapted to be exploited as a generator of a reference signal, the reference signal depending on a value of an electrical characteristic of the at least one reference cell. The method includes providing a population of auxiliary cells, operating on said population of auxiliary cells for varying a value of the electrical characteristic thereof, in such a way that the varied values are statistically distributed in a range including a value of the electrical characteristic corresponding to the reference signal, and choosing the at least one reference cell, wherein choosing includes choosing at least one auxiliary cell in the population of auxiliary cells having the value of the electrical characteristic close to the value corresponding to the reference signal with a pre-defined tolerance.