Semiconductor Memory Soft Program Voltage Control
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Solution Overview
Problem
Semiconductor memory technologies face inefficiencies in programming operations due to the wide distribution of threshold voltage in erased states, leading to high overdrive voltages that result in small changes in threshold voltage, requiring multiple program operations and increasing the time required for write operations.
Innovation Solution
A semiconductor memory system that includes a non-volatile memory cell with a floating gate, a state machine generating normal and soft program signals, a voltage generating circuit producing corresponding voltages, and a determination circuit to verify threshold voltage, allowing for a soft program operation with reduced overdrive voltage when necessary, thereby increasing the amount of threshold voltage change and reducing the number of program operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high overdrive voltage is applied during normal program operation, then the program operation can be performed, but the change in threshold voltage is small requiring multiple operations
Solution Approach 1:
The patent applies dynamics by switching between two different program voltage modes (normal and soft program) based on the memory transistor's threshold voltage state. The state machine dynamically selects the appropriate program signal and voltage level, transitioning from high overdrive voltage to lower overdrive voltage as the threshold voltage approaches the target value, thereby optimizing both programming efficiency and precision
Solution Approach 2:
The patent changes the program voltage parameter dynamically during the write operation. Initially, a high program voltage (e.g., 20V) is applied to achieve large threshold voltage changes. As the threshold voltage approaches the target value, the program voltage is reduced to a lower level (e.g., 12V) to achieve fine-grained adjustments, preventing overshoot and reducing total programming time
2Manufacturing precision
If multiple normal program operations are performed to achieve sufficient threshold voltage change, then the threshold voltage reaches the target value, but the write operation time increases
Solution Approach 1:
The patent implements periodic action through alternating normal program operations and verify operations. The state machine periodically switches between applying program voltage and performing verification, allowing the system to make progress toward the target threshold voltage while checking for completion. This periodic cycle is optimized by introducing soft program operations to reduce the number of full normal program cycles needed
Solution Approach 2:
The patent uses feedback through the verify operation to monitor the threshold voltage status and control the programming process. The determination circuit continuously checks whether the threshold voltage has reached the target value, and this feedback information is used by the state machine to decide whether to continue normal program operations or switch to soft program mode, ensuring precise control while minimizing operation time
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 approach reduces the time required for write operations and improves the performance of semiconductor memory by allowing for more significant changes in threshold voltage with fewer operations, especially for memory transistors with low threshold voltages in erased states.
Implementation Method 1
a voltage generating circuit configured to generate a normal program voltage and a verify voltage in response to the normal program signal and the verify signal respectively, and to generate a soft program voltage being lower than the normal program voltage in response to the soft program signal
Implementation Method 2
the control gate of the memory transistor is set to a high level in order to generate a hot electron in a channel region of the memory cell transistor. The threshold voltage of the memory transistor is high because the hot electron is injected into the floating gate of the memory transistor
Data Source
AI summary
A semiconductor memory includes: a non-volatile memory cell including a floating gate and a memory transistor; a state machine that generates a normal program signal for performing a normal program operation and a verify signal for performing a verify operation and generates a soft program signal for performing a soft program operation when detecting a fail in the verify operation after the normal program operation, whether a threshold voltage of the memory transistor reaches a value being checked in the verify operation; a voltage generating circuit that generates a normal program voltage and a verify voltage based on the normal program signal and the verify signal and generates a soft program voltage based on the soft program signal; and a determination circuit that detects a pass when the threshold voltage reaches the value and detects the fail when the threshold voltage does not reach the value.