Cross Point Memory Cell Array With Select Device
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Solution Overview
Problem
Existing memory technologies face challenges in maintaining the polarization state of ferroelectric capacitors during read operations, often requiring immediate re-write after reading, and phase change memory materials are limited by high temperatures for phase transitions.
Innovation Solution
An array of cross point memory cells is designed with spaced first and second lines, where two memory cells are individually positioned between adjacent second lines and a shared first line, incorporating a select device and a programmable device in series, with a shared first pillar electrode and programmable ferroelectric material, allowing for stable polarization states without immediate re-write.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ferroelectric capacitors are used for non-volatile memory storage, then data retention is improved, but the polarization state is reversed during read operations requiring immediate re-write
Solution Approach 1:
The memory array is segmented into multiple memory cells with individual select devices, allowing selective access to specific cells during read operations. This segmentation enables precise control over which cells are read, preventing unintended polarization reversal in non-accessed cells and reducing the need for blanket re-write operations.
Solution Approach 2:
A select device is introduced as an intermediary component between the read circuitry and the ferroelectric capacitor. This select device acts as a gate that controls current flow during read operations, enabling detection of the polarization state without directly applying read voltages that would reverse the polarization, thus eliminating the need for immediate re-write.
2Reliability
If phase change memory materials are used, then non-volatile storage is achieved, but high temperatures are required for phase transitions
Solution Approach 1:
The patent transitions from phase change materials to ferroelectric materials, changing the fundamental physical parameter used for data storage. Instead of relying on temperature-induced phase transitions requiring heating above 400°C, the invention uses electric field-induced polarization switching in ferroelectric capacitors, which operates at much lower temperatures and voltages.
Solution Approach 2:
The invention replaces the thermal-mechanical phase transition mechanism with an electrostatic polarization mechanism. Instead of using heat to change the physical phase of materials (mechanical/thermal system), the patent uses electric fields to switch the polarization state of ferroelectric material (electrostatic system), eliminating the need for high-temperature operations.
3Device complexity
If cross point memory cell array is configured with shared first pillar electrode, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
Adjacent memory cells share a common first pillar electrode, merging what would otherwise be separate components. This sharing reduces the total number of pillar electrodes in the array, simplifying the overall device structure and reducing manufacturing complexity while maintaining individual cell functionality through the select device control.
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 enables stable and non-volatile memory storage by maintaining polarization states without reversing them during read operations, improving data retention and reducing the need for immediate re-write, while also utilizing ferroelectric capacitors effectively.
Implementation Method 1
One type of capacitor is a ferroelectric capacitor which has ferroelectric material as at least part of the insulating material. Ferroelectric materials are characterized by having two stable polarized states and thereby can comprise programmable material of a memory cell.
Implementation Method 2
A capacitor has two electrical conductors separated by electrically insulating material. Energy as an electric field may be electrostatically stored within such material.
Implementation Method 3
Phase change memory uses a reversibly programmable material that has the property of switching between two different phases, for example between an amorphous disorderly phase and a crystalline or polycrystalline orderly phase. Phase change can be obtained by locally increasing the temperature of the chalcogenide.
Implementation Method 4
The two phases may be associated with resistivities of significantly different values. With chalcogenides, the resistivity may vary by two or more orders of magnitude when the material passes between the amorphous (more resistive) phase and the crystalline (more conductive) phase.
Data Source
AI summary
An array of cross point memory cells comprises spaced first lines which cross spaced second lines. Two memory cells are individually between one of two immediately adjacent of the second lines and a same single one of the first lines.