How Multi-Level Cell Memory Stores More Data in Less Space
Toshiba's 1999 patent describes a method for storing multiple bits of data in a single memory cell by precisely controlling voltage levels during programming.
Original patent title: “Semiconductor device and memory system”
Toshiba's 1999 patent describes a method for storing multiple bits of data in a single memory cell by precisely controlling voltage levels during programming. Granted to Toshiba Corp in 1999 with 64 claims and 326 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent details a technique for Multi-Level Cell (MLC) flash memory, where each memory cell can store more than one bit of data by using multiple distinct voltage thresholds. It describes a two-step programming process where the voltage bias applied to the cell increases in specific, controlled increments (ΔVpp1 and ΔVpp2). By using a smaller step-up value for the first programming phase and a larger one for the second, the device ensures the threshold voltage distributions remain accurate and distinct, allowing the cell to reliably hold values like '1', '2', or '3'.
The gap
What does this patent NOT cover?
- Does not cover Single-Level Cell (SLC) memory where each cell stores only one bit.
- Does not cover memory architectures that do not use stepwise bias increases for programming.
- Does not cover the physical manufacturing process of the silicon wafers themselves.
- Does not cover the specific error-correction algorithms used to read the data.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The innovation lies in using different step-up voltage increments (ΔVpp1 < ΔVpp2) for different stages of the programming cycle to maintain tight control over the voltage thresholds, preventing data overlap in high-density memory.
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
NAND flash memory chips
Solid State Drives (SSDs)
SD cards and microSD cards
Embedded flash memory in smartphones
Why it matters
The bigger picture
This technology is a foundational element of modern high-capacity flash storage. By allowing a single cell to represent multiple states, it enabled the transition from expensive, low-capacity storage to the dense NAND flash memory found in every smartphone, SSD, and USB drive today.
Filed
March 17, 1997
Granted
May 11, 1999
Market context
Who's building on this
Companies in this space
Toshiba (now Kioxia) remains a major player in this space. Other industry giants like Samsung, Micron, and SK Hynix have built upon these fundamental principles to develop even denser technologies like TLC (Triple-Level Cell) and QLC (Quad-Level Cell) memory.
Market impact
This patent helped trigger the shift toward high-density flash storage, effectively lowering the cost per gigabyte of memory. It became a critical piece of the intellectual property landscape that allowed the flash memory industry to scale up to the terabyte-level capacities common in modern computing.
Claim 1 — Plain English
What this patent covers
This patent details a technique for Multi-Level Cell (MLC) flash memory, where each memory cell can store more than one bit of data by using multiple distinct voltage thresholds. It describes a two-step programming process where the voltage bias applied to the cell increases in specific, controlled increments (ΔVpp1 and ΔVpp2). By using a smaller step-up value for the first programming phase and a larger one for the second, the device ensures the threshold voltage distributions remain accurate and distinct, allowing the cell to reliably hold values like '1', '2', or '3'.
The clever bit
The innovation lies in using different step-up voltage increments (ΔVpp1 < ΔVpp2) for different stages of the programming cycle to maintain tight control over the voltage thresholds, preventing data overlap in high-density memory.
What it does not cover
- Does not cover Single-Level Cell (SLC) memory where each cell stores only one bit.
- Does not cover memory architectures that do not use stepwise bias increases for programming.
- Does not cover the physical manufacturing process of the silicon wafers themselves.
- Does not cover the specific error-correction algorithms used to read the data.
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
Strong
Citation count
40/40
Highly cited
Claim breadth
20/20
Very broad protection
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
$90K – $288K
Midpoint $180K · expired or expiring · industry ×1.5
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
64 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Tanaka, T., & Takeuchi, K. (1999). How Multi-Level Cell Memory Stores More Data in Less Space (U.S. Patent No. 5,903,495). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/5903495/semiconductor-device-and-memory-system
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
Embed
Add this patent to your site
Drop this plain-English patent card into any blog post or article — free, no signup. It always links back to the full breakdown here.
<div data-patentlens-widget data-patent-number="US5903495"></div> <script src="https://patentbrief.org/embed.js" async></script>
Stay in the loop
Get a weekly digest of new patents.
One email per week. No spam. Unsubscribe anytime.
Keep exploring
Related patents you should know
US 4683195 · 1987
How to Make Billions of Copies of a DNA Segment
This patent describes the Polymerase Chain Reaction (PCR), a method to rapidly create many copies of a specific piece of DNA or RNA, enabling its detection and analysis.
Cetus Corp
US 8697359 · 2014
How to Edit Genes in Human Cells Using an Engineered CRISPR System
This patent describes an engineered CRISPR-Cas9 system for precisely cutting DNA in eukaryotic cells to change how genes work, opening the door for gene editing in complex organisms.
Massachusetts Institute of Technology
US 7657849 · 2010
How the iPhone's Slide-to-Unlock Gesture Works
Apple's 2010 patent describes unlocking a device by dragging a specific graphical image across the touchscreen along a predefined path, a gesture that became iconic with the original iPhone.
Apple Inc
US 4733665 · 1988
How Doctors Implant a Permanent Stent Using a Balloon
This patent describes the method for placing a permanent, expandable wire mesh tube inside a blood vessel or other body tube using a balloon-tipped catheter to widen it and keep it open.
Expandable Grafts Partnership
US 4965188 · 1990
How to Make Many Copies of a DNA Piece with Heat
This patent describes the Polymerase Chain Reaction (PCR) method, a technique to make millions of copies of a specific DNA segment using a heat-resistant enzyme and repeated temperature changes.
Cetus Corp
US 4235871 · 1980
How to Encapsulate Active Materials in Lipid Bubbles Efficiently
This patent describes a method for trapping biologically active substances inside tiny, multi-layered fat bubbles called liposomes, using a specific water-in-oil emulsion and gel-forming process to improve how much material gets captured.
Individual
Semantically similar
You might also find these interesting
US 4531203 · 1985 · Tokyo Shibaura Electric Co Ltd
How Flash Memory Cells Use an Erase Gate to Clear Data
US 3792322 · 1974
How Buried Channel CCDs Move Data Deep Inside Silicon Chips
US 9824092 · 2017 · Microsoft Technology Licensing LLC
How Microsoft Organizes Data in Multi-Tier Storage Systems
US 3387286 · 1968 · International Business Machines Corp
How Robert Dennard Invented the One-Transistor DRAM Memory Cell
More to explore
More in Semiconductors & Chips
US 5563422 · 1996 · Nichia Chemical Industries Ltd
How Nichia Created the First Practical Blue LED Electrodes
US 10373050 · 2019 · Qualcomm Inc
How to Make AI Run Faster on Smaller Computer Chips
US 2981877 · 1961 · Fairchild Semiconductor Corp
How Robert Noyce Invented the Modern Integrated Circuit
US 2569347 · 1951 · Bell Telephone Laboratories Inc
The Invention of the Junction Transistor
New to patents?
Common Questions
Frequently Asked Questions
What does How Multi-Level Cell Memory Stores More Data in Less Space cover?
Toshiba's 1999 patent describes a method for storing multiple bits of data in a single memory cell by precisely controlling voltage levels during programming.
Who owns patent US 5903495?
Toshiba Corp owns this patent, granted in 1999.
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 5903495 cited by?
This patent has been cited by 326 later patents that build on its ideas.
What problem does this patent solve?
This technology is a foundational element of modern high-capacity flash storage. By allowing a single cell to represent multiple states, it enabled the transition from expensive, low-capacity storage to the dense NAND flash memory found in every smartphone, SSD, and USB drive today.
What does this patent NOT cover?
Does not cover Single-Level Cell (SLC) memory where each cell stores only one bit.
Patent monitoring