Non-Volatile Memory Read Throughput via Word Line Voltage Propagation
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Solution Overview
Problem
The existing read operations in non-volatile semiconductor memory devices, such as NAND flash memory, face inefficiencies due to the delay caused by the propagation time of voltages along word lines, which affects throughput as all storage elements on a word line must reach a stable voltage level before sensing can begin, leading to longer read times and reduced performance.
Innovation Solution
The method involves applying a control gate voltage to a selected word line and sensing subsets of storage elements based on the propagation time, allowing earlier sensing of elements closer to the voltage source while ignoring or discarding data from elements that have not reached the stable voltage level, thereby optimizing read operations by dividing storage elements into subsets and synchronizing sensing with the voltage propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage is applied to the control gate and all storage elements must reach stable voltage before sensing, then sensing accuracy is ensured, but read operation time increases and throughput decreases
Solution Approach 1:
The patent segments the storage elements on the word line into multiple groups based on their distance from the voltage source. Elements closer to the source (which reach stable voltage faster) are sensed in an first subset, while elements farther away (which take longer to stabilize) are sensed in a second subset. This segmentation allows the sensing operation to proceed in stages rather than waiting for all elements to stabilize simultaneously, thereby reducing overall read time while maintaining sensing accuracy for each group.
2Measurement precision
If voltage propagation time is waited for before sensing, then data accuracy is improved, but throughput is reduced
Solution Approach 1:
The patent applies preliminary action by pre-establishing the voltage on the control gate and allowing it to propagate through the word line before initiating sensing operations. By dividing elements into subsets based on their expected voltage stabilization time, the system performs sensing actions at optimally timed moments rather than uniformly waiting for maximum propagation time. This enables earlier data availability from closer elements while maintaining accuracy requirements, thus improving throughput without sacrificing data accuracy.
3Reliability
If all storage elements are sensed after voltage stabilization, then read completeness is ensured, but read time increases
Solution Approach 1:
The patent segments the sensing operation into multiple phases corresponding to different subsets of storage elements. The first subset of elements (closer to the voltage source) is sensed earlier once they reach stable voltage, while the second subset (farther elements) is sensed later after their voltage stabilization. This segmented approach ensures that all elements are ultimately sensed (maintaining read completeness) while avoiding the delay of waiting for the slowest elements before starting any sensing operations, thereby reducing overall read time.
Data Source
AI summary
Read throughput is increased in a non-volatile memory device by sensing storage elements which are of interest as soon as a word line voltage has propagated to them, but before the word line voltage has propagated to other storage elements which are not of interest. The delay which would be incurred by waiting for the voltage to propagate along the entire word line is avoided. The sensing can occur during programming, as a verify operation, or after programming, as where user data is read. Further, the storage elements may be sensed concurrently, e.g., via sense amplifiers. Data from the storage elements of interest is processed and data from the other storage elements is discarded. A time for sensing the storage elements of interest can be set by identifying which storage elements are being verified or include data which is requested by a read command.