Lateral Poly Fuse Memory Cell Process Variation Compensation
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Solution Overview
Problem
Existing non-volatile memory technologies, such as EEPROMs, require additional process steps and masks, increasing manufacturing costs and complexity, while offering high yield but not being suitable for applications needing only a small number of bits of memory.
Innovation Solution
A lateral polysilicon programmable read-only memory cell with a fusible link memory element and a programming circuit that maintains a constant current density, independent of process variations, using a replica of the fusible link element and a programming current source to ensure reliable programming without extra process steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If EEPROM technology is used to achieve high-yielding non-volatile memory, then manufacturing yield is improved, but device complexity and manufacturing cost increase due to additional process steps and masks
Solution Approach 1:
The patent uses a replica fusible link element that copies the geometry and process variations of the actual memory element. This replica is used to generate a programming current that automatically compensates for process variations, eliminating the need for additional process steps while maintaining high yield through self-adjusting current density.
Solution Approach 2:
The patent introduces a current source that uses the replica element as an intermediary to translate process variations into compensating current adjustments. This intermediary mechanism allows the system to adapt to process variations without requiring additional manufacturing steps or masks.
2Use of energy by moving object
If metal fuses with thin cross sections are used to minimize programming current, then programming current is reduced, but device complexity increases due to extra masks and process steps
Solution Approach 1:
The patent changes the material parameter from metal to polysilicon, which has inherently lower programming current requirements due to its higher resistivity. This material substitution eliminates the need for thin cross-section geometry and associated process steps while achieving the same current reduction goal.
Solution Approach 2:
The replica polysilicon element copies the process variations of the actual element, allowing the system to optimize programming current through current density control rather than geometric thinning, thus avoiding additional process steps.
3Device complexity
If polysilicon fuse with larger cross section is used to simplify manufacturing, then device complexity is reduced, but programming current increases
Solution Approach 1:
The patent exploits the resistivity parameter of polysilicon, which is inherently higher than metal, to achieve low programming current with larger cross-section geometries. The current source further adjusts the current parameter based on replica element measurements to optimize the balance between geometry and current.
Solution Approach 2:
The current source acts as an intermediary that compensates for the increased current demand of larger cross-section polysilicon fuses by using feedback from the replica element to adjust and optimize the programming current density.
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 solution enables a high-yielding, voltage, and process-insensitive non-volatile memory cell that reduces manufacturing costs and complexity by maintaining a consistent programming current density, ensuring reliable operation across various geometries and process technologies.
Implementation Method 1
These early PROMs used the inherent high current characteristics of bipolar transistors to deliver sufficient current in the metal fuse such that metal migration would occur, causing an open circuit in the fuse
Implementation Method 2
The programming circuit includes a replica of the fusible link memory element and a programming current source for producing a known current density in the fusible link memory element in spite of variations including at least process variations
Data Source
AI summary
The present invention, generally speaking, provides for a non volatile memory cell requiring no extra process steps. In one embodiment, the non volatile memory cell is a lateral polysilicon programmable read only memory cell, in particular a lateral poly fuse memory cell. Technique are provided to achieve a high yielding, voltage, temperature, and process insensitive lateral poly fuse memory. In one embodiment, a fusible link memory circuit includes a fusible link memory element and a programming circuit. The programming circuit includes a replica of the fusible link memory element and a programming current source for producing a known current density in the fusible link memory element in spite of variations including at least process variations.