Non-Volatile Memory Read Current Stability via Post-Program Tuning
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Solution Overview
Problem
Non-volatile memory devices, such as split gate memory cells, face read current instability due to electron capture and emission by oxide traps, leading to random telegraph noise (RTN) that can decrease the threshold voltage and increase channel conductivity, affecting the accuracy of read operations after programming is completed.
Innovation Solution
A memory device with control circuitry that programs non-volatile memory cells to an initial state meeting a target threshold voltage, then performs post-program tuning by adjusting programming voltages based on read current measurements to compensate for RTN, ensuring the memory cell remains within a tolerable threshold voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If memory cells are programmed to meet a target threshold voltage, then programming precision is improved, but read current stability deteriorates due to RTN causing threshold voltage drops
Solution Approach 1:
The patent applies preliminary action by performing post-program tuning after initial programming to compensate for RTN effects. The system measures read current, detects threshold voltage drops caused by RTN, and applies additional programming pulses to restore the threshold voltage to the target level, thereby pre-compensating for the instability that would otherwise occur during normal operation
Solution Approach 2:
The patent implements feedback by measuring the read current after programming and using this measurement to determine whether additional programming is needed. The system continuously monitors the threshold voltage stability and adjusts the programming state accordingly, creating a closed-loop control system that maintains read current stability despite RTN effects
2Reliability
If post-program tuning is applied to compensate for RTN, then read current stability is improved, but device complexity increases due to additional programming steps
Solution Approach 1:
The patent applies self-service by enabling the memory cell to self-diagnose and self-correct its threshold voltage drift. The post-program tuning process allows the memory cell to automatically detect RTN-induced instability through read current measurement and self-adjust its programming state without requiring external intervention or complex control circuitry
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 stabilizes the read operation by ensuring the memory cell remains deeply programmed, reducing the likelihood of control gate threshold voltage drops below the target level, thus maintaining accurate programming state representation during read operations.
Implementation Method 1
Electrons will then flow along the channel region 18 from the drain region 16 toward the source region 14, with electrons becoming accelerated and heated whereby some of them are injected onto the floating gate 20 by hot-electron injection
Implementation Method 2
One source of read current instability in analog non-volatile memory devices is the capture and emission of electrons by oxide traps located at the interface and near-interface between the gate oxide and memory cell channel region
Data Source
AI summary
A memory device and method for a non-volatile memory cell having a gate that includes programming the memory cell to an initial program state corresponding to a target read current and a threshold voltage, including applying a program voltage having a first value to the gate, storing the first value in a memory, reading the memory cell in a first read operation using a read voltage applied to the gate that is less than the target threshold voltage to generate a first read current, and subjecting the memory cell to additional programming in response to determining that the first read current is greater than the target read current. The additional programming includes retrieving the first value from the memory, determining a second value greater than the first value, and programming the selected non-volatile memory cell that includes applying a program voltage having the second value to the gate.