Adaptive Memory Threshold Voltage Distribution for Cross-Temperature Read Margins
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Solution Overview
Problem
Memory systems, particularly NAND flash devices, face challenges in maintaining consistent performance and reliability across varying operating temperatures, leading to shifts in threshold voltage distributions that can result in loss of read margins.
Innovation Solution
Implementing a finer trim programming algorithm that adjusts the number of voltage steps and program pulses based on temperature ranges, using a second threshold voltage distribution with increased margins between voltage levels to improve read reliability at extreme temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard threshold voltage distribution is used for programming memory cells, then write operation speed is maintained, but read margins are lost at extreme temperatures due to voltage distribution overlap
Solution Approach 1:
The patent applies dynamics by making the threshold voltage distribution adaptive rather than fixed. The system dynamically selects between a first threshold voltage distribution (for normal temperature operation) and a second threshold voltage distribution (for extreme temperature operation) based on detected temperature conditions. This dynamic adaptation allows the memory system to optimize read margins at extreme temperatures while maintaining standard write performance at normal temperatures, resolving the contradiction between reliability and productivity.
Solution Approach 2:
The patent changes the parameters of the threshold voltage distribution based on operating conditions. Specifically, it modifies the voltage levels and spacing in the threshold voltage distribution according to temperature ranges. At extreme temperatures, the system transitions to a second distribution with adjusted parameters that prevent voltage overlap and preserve read margins, thereby improving reliability without permanently sacrificing write speed.
2Reliability
If temperature-compensated threshold voltage distribution is applied, then cross-temperature reliability is improved, but programming complexity increases
Solution Approach 1:
The patent segments the temperature operating range into distinct intervals (normal temperature range and extreme temperature range). For each segment, a predetermined threshold voltage distribution is assigned. This segmentation approach simplifies the programming algorithm by avoiding the need for continuous, complex calculations across the entire temperature spectrum. Instead, the system selects from predefined distributions based on which temperature segment is active, reducing programming complexity while maintaining cross-temperature reliability.
Solution Approach 2:
The patent applies preliminary action by pre-calculating and storing multiple threshold voltage distributions that are optimized for different temperature ranges. Rather than computing the appropriate distribution in real-time during programming operations, the system has these distributions prepared in advance. When programming occurs, the controller simply selects the appropriate pre-computed distribution based on the current temperature, significantly reducing the computational complexity of the programming algorithm.
3Reliability
If voltage steps are increased to maintain separation between threshold voltage distributions, then read reliability improves, but write operation time increases
Solution Approach 1:
The patent applies dynamics by adjusting the voltage step size based on the operating temperature range. During normal temperature operation, standard voltage steps are used, maintaining fast write speeds. During extreme temperature operation, the system dynamically increases the voltage steps to maintain adequate separation between threshold voltage distributions, thereby preserving read reliability. This dynamic adjustment of voltage step size resolves the contradiction between read reliability and write speed.
Data Source
AI summary
A memory device provides a memory array including memory cells, a temperature sensing circuit, and a memory control unit operatively coupled to the memory array. The memory control unit includes a processor. The processor is configured to receive temperature information from the temperature sensing circuit, initiate programming of the memory cells with data using a first threshold voltage distribution when the temperature information indicates an operating temperature is in a first temperature range, and initiate programming of the memory cells with data using a second threshold voltage distribution when the temperature information indicates the operating temperature is in a second temperature range.