Stacked Memory Driver Placement Above Arrays for Higher Density

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Solution Overview

Problem

In stacked memory arrays, the increasing number of memory cells and access lines requires more string drivers, but placing them underneath the array leads to complex routing and limited space, making it difficult to accommodate the increased number of drivers without expanding the integrated circuit die's footprint.

Innovation Solution

The string drivers are moved above the memory array, using monocrystalline semiconductors to reduce resistance and current leakage, and are formed and transferred to a surface above the dielectric using a transfer technique that avoids forming them on the dielectric surface, allowing for higher driver density and improved performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If string drivers are placed underneath the memory array, then routing is simplified, but the available space becomes limited and complex routing is required to accommodate increased number of drivers

Engineering Contradiction:

Improverouting complexityVSAvoidavailable space underneath array

Core Design Contradiction:

Device complexityVSArea of stationary object

Solution Approach 1:

The patent inverts the conventional placement location of string drivers from underneath the memory array to above the memory array. This inversion resolves the space constraint problem by utilizing the previously underutilized space above the array, while still maintaining manageable routing complexity through the introduced access lines that extend from data lines to the newly positioned drivers.

Inventive Principle:

Principle #13The other way round (Inversion)

2Area of stationary object

If the footprint of the integrated circuit die is kept constant, then device integration is maintained, but the number of string drivers that can be accommodated is limited

Engineering Contradiction:

Improvefootprint of integrated circuit dieVSAvoidnumber of string drivers

Core Design Contradiction:

Area of stationary objectVSQuantity of substance

Solution Approach 1:

The patent transitions from a two-dimensional planar arrangement to a three-dimensional vertical arrangement by placing string drivers above the memory array in multiple tiers. This dimensional change allows multiple drivers to be stacked vertically within the same footprint, thereby increasing the number of accommodated drivers without expanding the die area.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Quantity of substance

If more string drivers are added to support increased memory capacity, then memory capacity increases, but resistance and current leakage increase

Engineering Contradiction:

Improvememory capacityVSAvoidresistance and current leakage

Core Design Contradiction:

Quantity of substanceVSLoss of energy

Solution Approach 1:

The patent introduces access lines as intermediary conductors that connect data lines to the control gates of string drivers positioned above the array. These access lines serve as mediators that optimize the electrical connection path, reducing resistance and current leakage by providing direct, short-distance connections between the data lines and the control gates, thereby enabling increased driver density without proportional increases in energy loss.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12200938B2Driver placement in memories having stacked memory arrays

Publication Date: 2025.01.14 LODESTAR LICENSING GROUP LLC

AI summary

A memory can have a stacked memory array that can have a plurality of levels of memory cells. Each respective level of memory cells can be commonly coupled to a respective access line. A plurality of drivers can be above the stacked memory array. Each respective driver can have a monocrystalline semiconductor with a conductive region coupled to a respective access line.