NAND Flash — The Memory in Every SSD, iPhone, and USB Drive
Fujio Masuoka's 1987 Toshiba patent describes NAND flash memory — the non-volatile storage technology in every smartphone, SSD, and USB drive, invented over a weekend and presented at a conference Toshiba tried to block.
Original patent title: “Semiconductor memory device and method for manufacturing the same”
What this patent covers
The actual claim
This patent describes a NAND flash memory cell — a floating-gate transistor where charge can be stored on an electrically isolated 'floating gate' between the control gate and the semiconductor channel. Trapped charge on the floating gate shifts the transistor's threshold voltage, which can be sensed and decoded as a 0 or 1. To write data, high voltage is applied to inject electrons onto the floating gate (Fowler-Nordheim tunneling). To erase, high voltage of opposite polarity removes the stored charge. Cells are arranged in series strings (NAND configuration) — multiple cells share a single bit line, making the structure extremely dense. Unlike DRAM, the floating gate retains charge without power — NAND flash is non-volatile.
What this patent does NOT cover
The boundaries
- NOR flash — a different architecture where cells are arranged in parallel, allowing random bit-level access but with lower density than NAND
- 3D NAND (V-NAND) — stacking NAND cell layers vertically; the fundamental cell is the same but manufacturing is different
- Solid-state drive controllers and wear-leveling algorithms — the patent covers the cell structure, not the system to manage it
- EEPROM (electrically erasable programmable ROM) — a predecessor technology that erases byte-by-byte; NAND erases in blocks
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
Masuoka invented NAND flash in 1980 while working nights and weekends at Toshiba without approval or budget. He presented the concept publicly at the 1984 IEEE International Electron Devices Meeting — Toshiba management was furious because he had not cleared the presentation through their IP process. Intel had developed NOR flash earlier, which was random-access but expensive per bit. Masuoka's NAND arrangement connected cells in series rather than parallel — sacrificing random access for dramatically higher density and lower cost per bit. The 'flash' name came from Masuoka's colleague Shoji Ariizumi, who thought the erase process resembled the flash of a camera. Masuoka received a bonus of approximately $19,000 from Toshiba; he later sued the company and received a settlement of $758,000 — a fraction of the trillions NAND flash has generated.
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
The iPhone uses NAND flash for all storage — in 2007, Steve Jobs called it 'flash memory' and it was the key technology that let Apple eliminate the moving hard drive and build a thin phone
Modern SSDs (solid-state drives) replaced mechanical hard disks using NAND flash — read speeds increased from ~100MB/s to ~7,000MB/s and drives became shock-resistant and silent
USB drives, SD cards, and CF cards are all NAND flash in different form factors — the same cell Masuoka patented in 1987 stores your photos, music, and files
Why it matters
The bigger picture
NAND flash made the smartphone era possible. Mechanical hard drives — even the smallest 1.8-inch laptop drives — were too large, too fragile, and too power-hungry to put in a pocket device. NAND flash has no moving parts, survives drops, uses minimal power, and can be made in any shape. The cost per gigabyte of NAND flash has fallen by a factor of over 50,000 since commercialization in the late 1980s, following a version of Moore's Law specific to storage. Today NAND flash is manufactured by Samsung, SK Hynix, Micron, and Kioxia (Toshiba's spinoff) — the company that didn't appreciate what Masuoka invented.
Filed
November 13, 1981
Granted
July 23, 1985
Claim 1 — Plain English
What this patent covers
This patent describes a NAND flash memory cell — a floating-gate transistor where charge can be stored on an electrically isolated 'floating gate' between the control gate and the semiconductor channel. Trapped charge on the floating gate shifts the transistor's threshold voltage, which can be sensed and decoded as a 0 or 1. To write data, high voltage is applied to inject electrons onto the floating gate (Fowler-Nordheim tunneling). To erase, high voltage of opposite polarity removes the stored charge. Cells are arranged in series strings (NAND configuration) — multiple cells share a single bit line, making the structure extremely dense. Unlike DRAM, the floating gate retains charge without power — NAND flash is non-volatile.
The clever bit
Masuoka invented NAND flash in 1980 while working nights and weekends at Toshiba without approval or budget. He presented the concept publicly at the 1984 IEEE International Electron Devices Meeting — Toshiba management was furious because he had not cleared the presentation through their IP process. Intel had developed NOR flash earlier, which was random-access but expensive per bit. Masuoka's NAND arrangement connected cells in series rather than parallel — sacrificing random access for dramatically higher density and lower cost per bit. The 'flash' name came from Masuoka's colleague Shoji Ariizumi, who thought the erase process resembled the flash of a camera. Masuoka received a bonus of approximately $19,000 from Toshiba; he later sued the company and received a settlement of $758,000 — a fraction of the trillions NAND flash has generated.
What it does not cover
- NOR flash — a different architecture where cells are arranged in parallel, allowing random bit-level access but with lower density than NAND
- 3D NAND (V-NAND) — stacking NAND cell layers vertically; the fundamental cell is the same but manufacturing is different
- Solid-state drive controllers and wear-leveling algorithms — the patent covers the cell structure, not the system to manage it
- EEPROM (electrically erasable programmable ROM) — a predecessor technology that erases byte-by-byte; NAND erases in blocks
Patent Journey
From filing to expiry
Patent Filed
1981
Patent Granted
1985 · 4yr after filing
Patent Expired
2001
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 assignee
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
The original legal language
Original claims
5 claims as filed with the patent office.
Glossary
Key terms defined
- non-volatile
- Memory that retains data without power — NAND flash keeps your files when your phone is off, unlike DRAM
- floating gate
- An electrically isolated conductor between the control gate and transistor channel — trapped charge on it shifts the transistor's switching threshold, storing data
- NAND configuration
- Cells connected in series sharing a bit line, maximizing density — contrasted with NOR (parallel, faster access but lower density)
- Fowler-Nordheim tunneling
- Quantum mechanical effect where electrons tunnel through a thin oxide layer under high voltage — how data is written to NAND flash
Citations
Patent lineage
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