String Driver Placement Above Stacked Memory Arrays
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Solution Overview
Problem
In stacked memory arrays, the increasing number of string drivers required for higher memory density poses a challenge due to limited space under the array, leading to complex routing and performance degradation caused by high resistance and current leakage from using polycrystalline semiconductors.
Innovation Solution
The string drivers are placed above the memory array using monocrystalline semiconductors, which reduce resistance and current leakage, and are transferred to a surface above the memory array using a deposition technique that avoids forming semiconductors on dielectrics, allowing for higher driver density without increasing the integrated circuit die footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If string drivers are placed under the stacked memory array, then routing is simplified, but the available space becomes insufficient for higher memory density and routing complexity increases
Solution Approach 1:
The patent inverts the conventional placement of string drivers from underneath the memory array to above the memory array. This inversion resolves the space constraint issue by utilizing the previously underutilized space above the array, allowing for higher driver density without increasing the overall die footprint.
Solution Approach 2:
The patent transitions from a two-dimensional planar arrangement to a three-dimensional stacked architecture by placing string drivers above the memory array in the vertical dimension. This enables higher driver density by utilizing the vertical space above the array rather than being constrained to the horizontal plane underneath.
2Ease of manufacture
If polycrystalline semiconductors are used in string drivers, then manufacturing is easier, but resistance increases and current leakage occurs
Solution Approach 1:
The patent changes the material parameter from polycrystalline semiconductor to monocrystalline semiconductor. This material parameter change reduces resistance and current leakage while maintaining manufacturability, as monocrystalline materials offer superior electrical properties for driver circuits.
3Quantity of substance
If driver density is increased to achieve higher memory density, then memory capacity increases, but the die footprint increases
Solution Approach 1:
The patent utilizes the vertical dimension by placing string drivers above the memory array rather than only underneath. This three-dimensional arrangement allows for increased driver density and higher memory capacity without proportionally increasing the horizontal die footprint, effectively decoupling density from area.
Solution Approach 2:
By inverting the driver placement from below to above the memory array, the patent unlocks additional space for driver circuits. This inversion enables higher driver density within the same die footprint, thereby increasing memory capacity without expanding the overall device area.
Data Source
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.