Semiconductor Memory Erased Page Search Controller
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Solution Overview
Problem
Semiconductor memory devices face performance degradation due to read disturb, which occurs when repetitive read operations alter the threshold voltage distribution of memory cells, leading to reduced device performance and reliability.
Innovation Solution
A semiconductor memory device and controller system that employs a search read operation, where a read voltage is applied to multiple word lines including the selected page, and a pass voltage is applied to remaining word lines, reducing the impact of read disturb by minimizing the application of high pass voltage to unselected memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a read voltage is applied to a selected word line during a read operation, then data can be read from the memory device, but threshold voltage distribution of memory cells deteriorates due to read disturb
Solution Approach 1:
The patent segments the read operation into two distinct modes: normal read operations that apply read voltage to a single selected word line, and search read operations that apply read voltage to multiple unselected word lines simultaneously. This segmentation allows the system to use different voltage application strategies depending on the operational context, thereby reducing read disturb effects while maintaining data read capability.
Solution Approach 2:
The patent inverts the conventional approach by applying read voltage to unselected word lines (including multiple word lines) during search read operations, rather than only to the selected word line. This inversion enables the detection of initially erased pages by observing which word lines do not require high pass voltage, thus identifying the boundary between programmed and erased pages without causing significant read disturb to the selected page.
2Ease of operation
If pass voltage is applied to unselected word lines during read operations, then memory cells can be accessed, but performance degradation occurs due to read disturb
Solution Approach 1:
The patent dynamically adjusts the voltage application strategy based on the operational mode. During search read operations, the system applies read voltage to multiple unselected word lines and uses adaptive pass voltage levels, whereas during normal read operations, it uses the conventional approach of applying read voltage to only the selected word line. This dynamic adaptation optimizes performance by minimizing unnecessary high voltage applications that cause read disturb.
Solution Approach 2:
The patent changes the voltage parameters (read voltage and pass voltage levels) based on the operational context. During search read operations, different pass voltage levels are applied to different groups of word lines to efficiently identify initially erased pages while minimizing read disturb. The system monitors read results and adjusts subsequent voltage applications accordingly, thereby maintaining device performance while ensuring proper memory cell accessibility.
3Productivity
If repetitive read operations are performed on the same memory block, then data can be accessed multiple times, but threshold voltage distribution changes leading to performance degradation
Solution Approach 1:
The patent implements periodic search read operations to identify initially erased pages at intervals during normal operation. By periodically performing search read operations, the system can detect changes in the threshold voltage distribution caused by read disturb and identify affected memory regions. This periodic monitoring allows for timely intervention and adjustment of read strategies, thereby maintaining threshold voltage distribution stability while enabling frequent data access.
Data Source
AI summary
A controller controls an operation of a semiconductor memory device. The controller includes an erased page search controller, a command generator, and a data receiver. The erased page search controller determines a search mode of the semiconductor memory device, selects a page to search for, among a plurality of pages, based on the search mode, and generates a search control signal corresponding to a selected page. The command generator generates a search read command for the selected page based on the search control signal. The data receiver receives, from the semiconductor memory device, search read data corresponding to the search read command. The search read command is a command for controlling the semiconductor memory device to perform a read operation by applying a read voltage to multiple word lines including a word line corresponding to the selected page.