Semiconductor Memory Word Line Floating State Control
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Solution Overview
Problem
Nonvolatile semiconductor memory devices experience slow write and read speeds, but they maintain data even without a power supply, and there is a phenomenon where the channel of a memory block is boosted to a negative potential during discharge operations, affecting performance.
Innovation Solution
A semiconductor memory device with a pass circuit that connects local word lines to global word lines during operations and controls them to be in a floating state before discharging, preventing the channel from being boosted to a negative potential by using a voltage providing circuit to generate and apply operation voltages and then discharge the global word lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pass circuit is activated to connect local word lines to global word lines during operation, then the operation voltage can be properly applied to memory cells, but the channel may be boosted to a negative potential during discharge which affects performance
Solution Approach 1:
The patent segments the word line control into two independent levels: global word lines (GWL) and local word lines (LWL), each controlled separately by the pass circuit. This segmentation allows independent voltage management - the GWL can be discharged while the LWL remains floating, preventing the channel boost to negative potential that would occur if both were discharged simultaneously. The pass circuit acts as a segmentation barrier that isolates the discharge path.
Solution Approach 2:
The patent applies preliminary action by controlling the pass circuit to disconnect the local word lines from global word lines before discharging the global word lines. This preliminary disconnection prevents the discharge voltage from propagating to the local word lines and channel, thereby avoiding the negative potential boost. The pass circuit is activated during operation to connect the lines, then deactivated before discharge to isolate them.
2Speed
If the global word lines are discharged immediately after operation, then the voltage can be reset quickly, but the channel may be boosted to a negative potential which degrades performance
Solution Approach 1:
The pass circuit serves as an intermediary element between the global word lines and local word lines. During discharge, the pass circuit is deactivated to act as a barrier, preventing the discharge voltage from directly affecting the local word lines and channel. This intermediary control allows the global word lines to be discharged quickly while protecting the channel from negative potential boost, thus resolving the contradiction between speed and reliability.
Data Source
AI summary
The semiconductor memory device includes a memory block including a plurality of memory strings, a pass circuit connected between local word lines of the memory block and global word lines and configured to connect the local word lines to the global word lines in response to a block selection signal, and a voltage providing circuit configured to generate an operation voltage during a program or read operation, apply the operation voltage to the global word lines, and discharge the global word lines when the program operation or the read operation is completed, and the pass circuit is configured to control the local word lines to be in a floating state after the program operation or the read operation is completed and before discharging the global word lines.