Charge Trap Initialization for Nonvolatile Memory Reliability
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Solution Overview
Problem
Nonvolatile semiconductor memory devices with multi-valued memory cells face reliability issues due to process variations, leading to wide scatter in initial read current levels, which can result in unnecessary programming operations and incorrect data reading.
Innovation Solution
A method that initializes memory cells by reading and injecting charge into charge traps until they hold a predetermined minimum charge, narrowing the distribution of initial charges and allowing for uniform programming, reducing the number of programming operations and improving data reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If memory cells are programmed without initialization, then programming operations can be performed directly, but wide scatter in initial read current levels leads to increased number of programming operations and reduced reliability
Solution Approach 1:
The patent applies preliminary action by initializing all charge traps to a standard initial state (charge level of 0 or 1) before programming operations begin. This preliminary initialization step ensures that all memory cells start from a known, uniform state, eliminating the wide scatter in initial read current levels that would otherwise require multiple programming operations to correct. The initialization is performed once at the beginning, preventing the need for repeated programming operations throughout the data writing process.
2Reliability
If alternating program-verify cycles are used for multiple charge traps, then all charge traps can be programmed, but current windows narrow due to charge trap interactions
Solution Approach 1:
The patent applies local quality by making the programming process trap-dependent. After initialization, the system determines the initial state of each charge trap individually and applies different programming sequences to different traps based on their specific requirements. This allows the system to maintain wide current windows by preventing unnecessary programming of already-correct traps, while still achieving complete programming of all traps. The verify operation detects which traps need programming, and only those traps receive programming pulses, eliminating the harmful interactions that occur when all traps are programmed uniformly.
3Ease of manufacture
If uniform programming voltages are applied to all charge traps, then programming process is simplified, but process variations cause wide scatter in read current levels
Solution Approach 1:
The patent applies feedback by implementing a verify operation that measures the read current of each charge trap and compares it against threshold values to determine the current data state. This feedback mechanism allows the system to detect process variations and adjust the programming process accordingly. The verify operation provides real-time information about which charge traps need programming and what programming level is required, enabling the system to compensate for manufacturing variations and achieve uniform read current levels across all memory cells despite process variations.
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
The method reduces the number of programming operations and enhances data reliability by ensuring all charge traps reach a consistent initial state, thereby maintaining a wider current window for accurate data discrimination.
Implementation Method 1
memory cells have charge traps that hold charge representing data values
Implementation Method 2
If the gate voltage is sufficiently high, hot electrons are injected into the charge trap and its data value changes to '0'
Implementation Method 3
If the charge trap has been programmed, the charge of the electrons stored in the charge trap acts counter to the positive gate voltage, reducing the current flow
Data Source
AI summary
A nonvolatile semiconductor memory device of the charge trap type is initialized by reading the memory cells in the device to determine which charge traps hold less than a predetermined minimum charge and injecting charge into these charge traps until all of the charge traps in the device hold at least the predetermined minimum charge. The charge traps are then programmed selectively with data. The initialization procedure shortens the programming procedure by narrowing the initial distribution of charge in the charge traps, and leads to more reliable reading of the programmed data.