Metal Grain Charge Storage Layer for Nonvolatile Memory
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Solution Overview
Problem
Nonvolatile semiconductor storage devices with charge storage parts across multiple memory cells face issues with charge leakage and varying transistor on/off voltage thresholds as the structure becomes finer, leading to challenges in data retention and memory window width.
Innovation Solution
A nonvolatile semiconductor storage device with a charge storage layer containing fine metal grains, where a differential voltage is applied across the semiconductor layer and gate electrode to store positive electric charges, utilizing the Coulomb blockade phenomenon to suppress electron injection and enhance charge holding, resulting in a wider memory window and longer data holding time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the structure becomes finer to increase storage density, then storage capacity is improved, but charge leakage between memory cells increases and transistor voltage threshold varies
Solution Approach 1:
The charge storage layer is segmented into discrete metal grains (nanoscale particles) rather than a continuous layer. Each grain acts as an independent charge storage unit, preventing charge migration between adjacent memory cells while maintaining high storage density. This segmentation resolves the charge leakage problem inherent in finer continuous structures.
Solution Approach 2:
The patent introduces metal grains with specific local properties (nanoscale size, discrete distribution) into the charge storage layer. These localized metal grain structures create unique electrostatic conditions that enable individual charge confinement, improving charge retention reliability at fine structures while maintaining high storage density.
2Ease of manufacture
If the charge storage layer uses a continuous structure, then manufacturing is simpler, but charge moves between memory cells causing voltage threshold variation
Solution Approach 1:
The patent changes the physical state and distribution parameters of the charge storage material from a continuous layer to discrete nanoscale metal grains. This parameter change (from continuous to discrete structure) enables precise charge confinement at the nanoscale while remaining compatible with existing semiconductor manufacturing processes through controlled deposition methods.
3Productivity
If electron injection is not suppressed, then charge storage is easier, but charge holding time decreases and memory window narrows
Solution Approach 1:
The discrete metal grain structure creates preliminary electrostatic barriers (Coulomb blockade effects) that prevent subsequent electron injection into already-filled grains. This preliminary anti-action mechanism suppresses further charge injection once grains are filled, thereby extending charge holding time and maintaining a wide memory window while preserving efficient charge storage capability.
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 solution effectively increases the charge storage quantity and holding time, enabling a wider memory window and longer data retention, facilitating multi-value memory operations while maintaining a finer structure.
Implementation Method 1
utilizing the Coulomb blockade phenomenon to suppress electron injection and enhance charge holding
Data Source
AI summary
A nonvolatile semiconductor storage device includes a semiconductor layer, a first insulating film formed on the semiconductor layer, a charge storage layer formed on the first insulating film and having fine metal grains, a second insulating film formed on the charge storage layer, and a gate electrode formed on the second insulating film. During a write operation, a differential voltage is applied across the gate electrode and the semiconductor layer to place the gate electrode at a lower voltage than the semiconductor layer and cause a positive electric charge to be stored in the charge storage layer.