Non-volatile Memory Soft Program Verify Voltage Adjustment
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Solution Overview
Problem
As flash memory geometries scale down, gm degradation due to increasing program and erase cycling leads to longer erase times, particularly in data storage applications that require a high number of cycles, necessitating a tighter threshold voltage (Vt) distribution during soft programming.
Innovation Solution
Implementing a dynamically adjustable soft program verify voltage level based on the number of cycles, allowing for a lower verify voltage in blocks with fewer cycles to reduce erase times and a higher verify voltage in blocks with many cycles to maintain a tight Vt distribution and mitigate column leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If soft programming is applied to tighten the Vt distribution of erased cells, then the Vt distribution becomes tighter, but erase times increase
Solution Approach 1:
The patent applies dynamics by making the soft program verify voltage level adjustable rather than fixed. The verify voltage is dynamically selected from multiple levels based on the number of program/erase cycles the memory block is expected to undergo. This allows the system to adapt the Vt distribution tightness requirement to the specific application scenario, resolving the contradiction between achieving tight Vt distribution and maintaining fast erase times.
Solution Approach 2:
The patent changes the parameter of verify voltage level from a single fixed value to multiple selectable levels. By providing different verify voltage levels (e.g., first level for high-cycle blocks, second level for low-cycle blocks), the system can adjust the soft programming intensity to match the application requirements, thereby optimizing the balance between Vt distribution quality and erase speed.
2Reliability
If a higher soft program verify voltage level is used to ensure tight Vt distribution, then column leakage is reduced, but erase times increase
Solution Approach 1:
The patent applies local quality by differentiating the soft programming requirements for different memory blocks based on their expected usage patterns. Blocks expected to undergo many cycles receive higher verify voltage levels for tighter Vt distribution and better leakage mitigation, while blocks with fewer cycles use lower verify voltage levels for faster erasure. This localized approach optimizes reliability only where needed without unnecessarily increasing erase times for all blocks.
Solution Approach 2:
The patent changes the verify voltage parameter based on the number of expected program/erase cycles. By selecting from multiple verify voltage levels according to the cycle count, the system adjusts the degree of Vt distribution tightening to match the actual reliability requirements, avoiding excessive erase times for blocks that don't need tight distributions.
3Area of moving object
If geometry scaling continues, then memory density increases, but gm degradation becomes more significant
Solution Approach 1:
The patent addresses gm degradation from geometry scaling by implementing a dynamic verify voltage selection mechanism. As geometries scale and gm degradation becomes more significant, the system can dynamically adjust the verify voltage level based on the number of cycles, allowing for tighter Vt distributions when needed to compensate for the degraded gm characteristics in scaled technologies.
Data Source
AI summary
An erase operation in a non-volatile memory includes selecting a block on which to perform an erase operation, erasing the selected block, receiving test data corresponding to the selected block, determining a soft program verify voltage level based on the test data, and soft programming the erased selected block using the soft program verify voltage level. A non-volatile memory includes a plurality of blocks, a test block which stores test data corresponding to each of the plurality of blocks, and a flash control coupled to the plurality of blocks and the test block, the flash control determining a soft program verify voltage level for a particular block of the plurality of blocks based on the test data for the particular block when the particular block is being soft programmed.