4CPP Bitcell Layout for MRAM Memory Element Placement
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Solution Overview
Problem
The one-transistor one-memory element design for MRAM bitcells faces manufacturing challenges due to the inability to shrink the back-end-of-line metal stack in line with advanced technology nodes, resulting in a large rectangular footprint and offset placement of the magnetoresistive memory element, which hinders design options.
Innovation Solution
A bitcell structure with a field-effect transistor having gate electrodes in a four contacted (poly) pitch layout, integrated with an interconnect structure that centrally places a memory element, allowing for balanced component placement and flexible design options.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the gate pitch is scaled to shrink the field-effect transistor dimension, then the transistor size is reduced, but the back-end-of-line metal stack cannot be commensurately shrunk, resulting in a large rectangular footprint
Solution Approach 1:
The patent transitions from conventional planar layouts (2CPP, 1.5CPP) to a four contacted (poly) pitch layout that utilizes vertical stacking and three-dimensional interconnect structures. This dimensional change allows the memory element to be centrally positioned while accommodating the fixed-size metal stack, effectively decoupling the scaling of transistors from the overall bitcell footprint.
Solution Approach 2:
The patent implements a nested structure where the memory element is positioned at the center of the bitcell and the interconnect structure is arranged around it in multiple layers. The field-effect transistors are positioned at the corners, creating a compact nested arrangement that optimizes space utilization and allows central placement of the memory element despite the fixed metal stack dimensions.
2Ease of manufacture
If the magnetoresistive memory element is placed proximate to an outer boundary in conventional layouts, then the layout is simplified, but design options are hindered and placement is offset from center
Solution Approach 1:
The patent employs asymmetric positioning of components within the bitcell, with the memory element centrally located and the four field-effect transistors positioned at the corners. This asymmetric arrangement provides design flexibility and allows for optimized signal routing and interconnect placement, enabling various design options while maintaining manufacturability.
Solution Approach 2:
The four contacted (poly) pitch layout creates a universal bitcell structure that can accommodate different memory element types (magnetoresistive, resistive, phase-change) and supports various interconnect configurations. The centralized memory element position and corner transistor arrangement provide a flexible template that can be adapted to multiple design requirements and technology nodes.
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 4CPP layout enables a more compact and centrally placed memory element within the bitcell, improving manufacturability and design flexibility, while maintaining the non-volatile memory functionality of MRAM or ReRAM elements.
Implementation Method 1
A magnetic random access memory (MRAM) device provides an embedded non-volatile memory technology in which the memory elements operate based on principles of magnetoresistance. The magnetoresistive memory element of each bitcell includes a pinned layer and a free layer, each of which holds a magnetization.
Implementation Method 2
The magnetoresistive memory element of each bitcell includes a pinned layer and a free layer, each of which holds a magnetization. The magnetization of the pinned layer is fixed in its magnetic orientation, and the magnetization of the free layer can be switched
Data Source
AI summary
Structures for a bitcell of a non-volatile memory and methods of fabricating such structures. A field-effect transistor of the bitcell includes a gate having gate electrodes that are arranged in a four contacted (poly) pitch layout. An interconnect structure is arranged over the field-effect transistor, and a memory element arranged in the interconnect structure. The memory element is connected by the interconnect structure with the field-effect transistor.