Flash Memory Voltage Reference Generator Using Big Flash Cells
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Solution Overview
Problem
Multi-level cell flash memory devices face challenges in generating precise wordline voltages efficiently, particularly in achieving fast stabilization times and resisting systematic offset, which affects the reliability and accuracy of data storage.
Innovation Solution
A high-precision voltage reference generator using Big Flash Cell circuits and cascaded current mirrors, combined with source followers in closed and open loops, generates precise reference voltages that can be trimmed to match the threshold voltage of flash cells, ensuring fast stabilization and reduced impact ionization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional voltage reference generators are used in multi-level cell flash memory, then device complexity is reduced, but manufacturing precision and reliability deteriorate due to inability to achieve fast stabilization times and resist systematic offset
Solution Approach 1:
The voltage reference generator is divided into multiple independent voltage reference circuits, each generating a specific reference voltage (Vref1, Vref2, Vref3). This segmentation allows each circuit to be optimized for its specific function, achieving fast stabilization and high precision while maintaining manageable overall complexity through modular design.
Solution Approach 2:
The patent employs multiple voltage reference circuits with different threshold voltages (Vt1, Vt2, Vt3) to generate reference voltages suitable for different wordline voltage requirements. By changing the parameter of threshold voltage across different circuits, the system achieves precise control over multiple voltage levels needed for multi-level cell operation.
2Productivity
If voltage reference generators are designed for fast stabilization, then productivity improves, but reliability worsens due to increased impact ionization
Solution Approach 1:
The patent introduces intermediate voltage reference circuits that act as mediators between the power supply and the wordline. These intermediate reference circuits with different threshold voltages distribute the voltage stress more evenly, reducing peak electric fields that cause impact ionization while still achieving fast stabilization through optimized circuit design.
Solution Approach 2:
By varying the threshold voltage parameter across different reference circuits (Vt1 < Vt2 < Vt3), the system optimizes the balance between stabilization speed and reliability. Lower threshold voltage circuits provide faster response, while higher threshold voltage circuits reduce impact ionization, and their combination achieves both goals simultaneously.
Data Source
AI summary
There is disclosed example embodiments of flash memory including reference generators using big flash memory cells to generate flash array wordline voltages, wherein the reference voltage values can be trimmed by changing the threshold voltage of the flash cells. In addition, the inventive subject matter provides for using the matching characteristics of two source followers in closed loop and open loop to achieve fast stabilization times. Further, the temperature characteristics of the wordline voltages track the temperature characteristics of the array flash cells. Still further, the disclosed reference generators use cascoding reference generators to provide more reliability and accuracy.