Flash Memory Programming Method Using Dual Verify Voltages
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Solution Overview
Problem
Current semiconductor memory devices, particularly flash memory devices, face challenges in efficiently programming multi-level cells to store multiple bits, requiring precise threshold-voltage control which is not adequately addressed by existing technologies.
Innovation Solution
A programming method for flash memory devices that involves a first programming operation followed by a second programming operation using a verifying voltage higher than the first, allowing for the storage of two-bit data without verifying the highest threshold-voltage distribution, and a nonvolatile memory device configuration that includes a memory cell array, reading/programming circuit, data buffer, and controller to manage these operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-level cell technology is implemented to increase storage capacity, then information storage capacity is improved, but threshold-voltage control precision requirements increase
Solution Approach 1:
The programming process is divided into multiple stages with different verifying voltages. The first programming operation uses a first verifying voltage to program memory cells to a first threshold-voltage distribution, then a second programming operation uses a second verifying voltage to program memory cells to a second threshold-voltage distribution. This segmentation allows precise control of threshold voltages for different data states in MLC technology.
Solution Approach 2:
The patent changes the verifying voltage parameter between programming operations. The second verifying voltage is higher than the first verifying voltage, enabling differentiation between multiple threshold-voltage distributions. This parameter change approach allows the same memory cell to be programmed to different threshold-voltage levels corresponding to different data values.
2Manufacturing precision
If additional data buffer is added to store original data for second programming operation, then programming precision is improved, but device complexity increases
Solution Approach 1:
The data buffer performs multiple functions: it stores data to be programmed during the first programming operation, stores original data retrieved from memory cells, and provides data for the second programming operation. This multi-functionality eliminates the need for separate storage structures, reducing device complexity while maintaining programming precision.
Solution Approach 2:
The patent combines the functions of storing program data and storing original data into a single data buffer structure. By merging these storage functions, the patent avoids adding additional buffer memory, thereby reducing device complexity while still enabling the second programming operation with reference to original data.
3Manufacturing precision
If second programming operation is performed with higher verifying voltage, then threshold-voltage distribution precision is improved, but programming time increases
Solution Approach 1:
The first programming operation is performed as a preliminary step to program memory cells to a first threshold-voltage distribution. This preliminary programming establishes a baseline state, allowing the second programming operation with higher verifying voltage to focus on achieving the precise second threshold-voltage distribution without starting from scratch, thus reducing total programming time.
Solution Approach 2:
The patent implements continuous programming operations where the data buffer maintains data availability between operations. The original data retrieved after the first programming operation is immediately available for the second programming operation, ensuring continuous useful action without idle time, thereby minimizing the time penalty of the multi-stage programming process.
Data Source
AI summary
Disclosed is a nonvolatile memory device and programming method of a nonvolatile memory device. The programming method of the nonvolatile memory device includes conducting a first programming operation for a memory cell, retrieving original data from the memory cell after the first programming operation, and conducting a second programming operation with reference to the original data and a second verifying voltage higher than a first verifying voltage of the first programming operation.