You can freely build on How Flash Memory Cells Use an Erase Gate to Clear Data

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.

What is now free to use

All 0 claims of US 4531203 are in the public domain. Specifically:

The 0 dependent claims 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 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.

Who is building on this today

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.

Products built on expired version of this technology

How to cite this patent in your documentation

Tokyo Shibaura Electric Co Ltd. US Patent 4531203. Semiconductor memory device and method for manufacturing the same. Granted 1985, expired 2002. 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.