How Flash Memory Cells Use an Erase Gate to Clear Data
This 1985 patent describes the foundational structure of flash memory, introducing an 'erase gate' that allows data to be electrically wiped from a memory cell.
Original patent title: “Semiconductor memory device and method for manufacturing the same”
This 1985 patent describes the foundational structure of flash memory, introducing an 'erase gate' that allows data to be electrically wiped from a memory cell. Granted to Tokyo Shibaura Electric Co Ltd in 1985 with 5 claims and 27 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
The patent defines a memory cell structure that includes a floating gate for storing data and a control gate for managing access. Crucially, it adds an erase gate that sits on a field insulation film. By placing this erase gate next to the floating gate, the device can use electrical charges to remove data from the floating gate. The patent specifies that the insulating film between the erase gate and the control gate must be thicker than the film between the floating gate and the erase gate to prevent short circuits during operation.
The gap
What does this patent NOT cover?
- Does not cover memory cells that rely solely on ultraviolet light for erasure (EPROM).
- Does not cover non-semiconductor storage media like magnetic hard drives.
- Does not cover the specific software logic used to manage data file systems.
- Does not cover memory architectures that lack a dedicated erase gate structure.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
By creating a specific, thicker insulating layer between the erase gate and the control gate, the inventors solved the problem of electrical interference, allowing the erase gate to function without disrupting the control gate's ability to read or write data.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
USB flash drives
Solid State Drives (SSDs)
MicroSD cards
Smartphone internal storage
Why it matters
The bigger picture
This invention by Fujio Masuoka at Toshiba is the ancestor of modern NAND flash memory. It shifted the industry away from memory that required bulky UV light erasers toward chips that could be wiped and rewritten instantly with electricity, enabling the portable storage we use today.
Filed
November 13, 1981
Granted
July 23, 1985
Market context
Who's building on this
Companies in this space
Companies like Kioxia (formerly Toshiba Memory), Samsung, Micron, and SK Hynix continue to evolve the architecture described here. They have scaled this basic cell design into the 3D NAND structures that allow for terabytes of storage in tiny chips.
Market impact
This patent enabled the transition to electrically erasable memory, which effectively killed off older, slower storage technologies. It laid the technical groundwork for the entire mobile computing revolution by making high-density, non-volatile data storage small and reliable enough for consumer devices.
Claim 1 — Plain English
What this patent covers
The patent defines a memory cell structure that includes a floating gate for storing data and a control gate for managing access. Crucially, it adds an erase gate that sits on a field insulation film. By placing this erase gate next to the floating gate, the device can use electrical charges to remove data from the floating gate. The patent specifies that the insulating film between the erase gate and the control gate must be thicker than the film between the floating gate and the erase gate to prevent short circuits during operation.
The clever bit
By creating a specific, thicker insulating layer between the erase gate and the control gate, the inventors solved the problem of electrical interference, allowing the erase gate to function without disrupting the control gate's ability to read or write data.
What it does not cover
- Does not cover memory cells that rely solely on ultraviolet light for erasure (EPROM).
- Does not cover non-semiconductor storage media like magnetic hard drives.
- Does not cover the specific software logic used to manage data file systems.
- Does not cover memory architectures that lack a dedicated erase gate structure.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Early stage
Citation count
29/40
Moderately cited
Claim breadth
3/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$13K – $40K
Midpoint $25K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
The original legal language
Original claims
5 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Iizuka, H., & Masuoka, F. (1985). How Flash Memory Cells Use an Erase Gate to Clear Data (U.S. Patent No. 4,531,203). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/4531203/nand-flash-memory
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Flash Memory Cells Use an Erase Gate to Clear Data cover?
This 1985 patent describes the foundational structure of flash memory, introducing an 'erase gate' that allows data to be electrically wiped from a memory cell.
Who owns patent US 4531203?
Tokyo Shibaura Electric Co Ltd owns this patent, granted in 1985.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 4531203 cited by?
This patent has been cited by 27 later patents that build on its ideas.
What problem does this patent solve?
This invention by Fujio Masuoka at Toshiba is the ancestor of modern NAND flash memory. It shifted the industry away from memory that required bulky UV light erasers toward chips that could be wiped and rewritten instantly with electricity, enabling the portable storage we use today.
What does this patent NOT cover?
Does not cover memory cells that rely solely on ultraviolet light for erasure (EPROM).
Patent monitoring