Flash Memory Quick Charge Loss Reduction via Negative Bias Pulse
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Solution Overview
Problem
Flash memory devices experience quick charge loss after programming, leading to immediate threshold voltage shifts and reduced data retention, which enlarges the threshold voltage distribution, affecting the number of programmable states in multi-level cell devices and increasing the risk of reading errors.
Innovation Solution
Applying a negative bias pulse to the selected word line prior to the program verify pulse forces trapped electrons from the tunnel oxide back into the channel region, ensuring that only the charge on the floating gate affects the threshold voltage measurement during verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If programming pulses are applied to increase the floating gate charge level, then the cell threshold voltage increases to the desired programmed level, but quick charge loss causes the threshold voltage to shift lower after programming
Solution Approach 1:
A preliminary action is performed by applying a negative bias pulse to the control gate before the verify operation. This negative bias forces trapped electrons in the tunnel oxide back into the channel region, eliminating the quick charge loss effect before verification occurs, thereby ensuring accurate threshold voltage measurement and improving data retention reliability
Solution Approach 2:
The parameter change involves modifying the control gate voltage by applying a negative bias pulse. This changes the electrical state of the tunnel oxide and floating gate system, forcing trapped electrons to move from the tunnel oxide into the channel region, thereby stabilizing the threshold voltage and preventing quick charge loss
2Reliability
If the threshold voltage distribution is enlarged to accommodate quick charge loss, then all possible threshold voltages can be accommodated, but the number of programmable states in multi-level cell devices is reduced
Solution Approach 1:
By applying the negative bias pulse as a preliminary action before verification, the quick charge loss is eliminated in advance. This prevents the need to enlarge the threshold voltage distribution, thereby maintaining tight voltage distributions that support more programmable states in multi-level cell devices without compromising reliability
3Reliability
If a negative bias pulse is applied to force trapped electrons back into the channel region, then quick charge loss is reduced and threshold voltage is maintained, but an additional programming step is required
Solution Approach 1:
The negative bias pulse application is merged with the existing verify operation sequence. The negative bias is applied immediately before the verify pulse, combining the charge stabilization function with the verification process. This integration minimizes additional complexity while ensuring accurate threshold voltage measurement and improved data retention
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method reduces the effects of quick charge loss, maintaining the programmed threshold voltage and preventing distribution shifts, thereby enhancing data retention and reducing errors in multi-level cell devices.
Implementation Method 1
a negative voltage pulse is applied to force trapped electrons from the tunnel oxide back into the channel region
Data Source
AI summary
Methods for reducing quick charge loss effects, methods for programming, memory devices, memory devices, and memory systems are disclosed. In one such method, a programming pulse is applied to the word line to increase the threshold voltage of the memory cells being programmed. A negative voltage pulse is applied to the word line after the programming pulse to force any electrons trapped in the tunnel oxide of memory cells being programmed back into the tunnel region. After the negative pulse, a program verify operation is performed.