You can freely build on How Multi-Level Cell Memory Stores More Data in Less Space
This patent expired in 2017. Every claim — 0 independent, 1 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
Toshiba Corp
Patent granted
1999
Expired
2017
Forward citations
326
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'.
What is now free to use
All 1 claims of US 5903495 are in the public domain. Specifically:
The 1 dependent claim add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
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.
Who is building on this today
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.
Products built on expired version of this technology
NAND flash memory chips
Solid State Drives (SSDs)
SD cards and microSD cards
Embedded flash memory in smartphones
How to cite this patent in your documentation
Toshiba Corp. US Patent 5903495. Semiconductor device and memory system. Granted 1999, expired 2017. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.