Floating-Gate Memory Cell Layout for Higher Coupling Ratio
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Solution Overview
Problem
The efficiency of programming and erasing operations in flash memory cells is limited by the coupling ratio between the control gate and the floating gate, which is constrained by the capacitance ratio of the gate dielectric and interlevel dielectric layers, necessitating an enhancement of the control gate-floating gate capacitance to improve operational efficiency.
Innovation Solution
The method involves forming gate stacks with specific configurations, including openings and separate portions, to increase the surface area of the dielectric layer between the floating gate and control gate electrodes, thereby enhancing the control gate-floating gate capacitance and coupling ratio, and using a dielectric film with an ONO structure to reduce junction leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the gate dielectric and interlevel dielectric layer thicknesses are reduced to scale down memory cells, then memory array density increases, but the control gate-floating gate capacitance decreases, reducing programming and erasing efficiency
Solution Approach 1:
The patent transitions from a planar gate structure to a three-dimensional vertical gate stack structure. The gate electrode extends vertically through multiple dielectric layers (tunnel dielectric, charge trap dielectric, blocking dielectric), creating a vertical capacitance path that increases effective coupling area without increasing lateral footprint, thus maintaining programming efficiency while enabling higher density
Solution Approach 2:
The patent employs a composite dielectric structure consisting of multiple functional layers: tunnel dielectric (for charge injection), charge trap dielectric (for charge storage), and blocking dielectric (for charge retention). This composite structure optimizes both capacitance coupling for programming efficiency and charge retention for data reliability, resolving the contradiction between density and efficiency
2Reliability
If the control gate-floating gate capacitance is increased to improve programming efficiency, then the coupling ratio improves, but the device complexity increases due to additional gate structures
Solution Approach 1:
The gate structure is segmented into distinct functional components: tunnel dielectric layer, charge trap dielectric layer, blocking dielectric layer, and control gate electrode. Each segment performs a specific function, allowing independent optimization of capacitance coupling and charge retention while maintaining overall structural organization and manufacturability
Solution Approach 2:
The vertical gate stack structure serves multiple functions simultaneously: it provides capacitance coupling for programming, charge storage for data retention, and electrical isolation between adjacent memory cells. This multi-functionality reduces the need for separate structures, thereby managing complexity while achieving improved programming efficiency
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 configuration increases the coupling ratio, reduces leakage currents, and improves data retention by increasing the control gate-floating gate capacitance and minimizing drain disturb, leading to more efficient programming and erasing operations.
Implementation Method 1
The memory device includes a dielectric layer over the floating gate electrode. The control gate electrode has a first portion interposed between the first and second portions of the floating gate electrode. This configuration increases the coupling ratio, reduces leakage currents, and improves data retention by increasing the control gate-floating gate capacitance
Data Source
AI summary
A memory device is provided. The memory device includes a semiconductor substrate, a tunneling layer, a floating gate electrode, a dielectric layer, and a control gate electrode. The semiconductor substrate has an active region. The tunneling layer is over the active region of the semiconductor substrate. The floating gate electrode is over the tunneling layer. The floating gate electrode has a first portion and a second portion electrically connected to the first portion. The dielectric layer is over the floating gate electrode. The control gate electrode is over the dielectric layer. The control gate electrode has a first portion interposed between the first and second portions of the floating gate electrode.