# 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. - **Patent:** US 4531203 - **Original title:** Semiconductor memory device and method for manufacturing the same - **Owner:** Tokyo Shibaura Electric Co Ltd - **Granted:** 1985 - **Status:** Public domain (expired) - **Times cited:** 27 - **Field:** semiconductors, consumer_electronics ## What it does 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 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. ## 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. ## Real-world examples 1. USB flash drives 2. Solid State Drives (SSDs) 3. MicroSD cards 4. Smartphone internal storage ## Why it matters 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. ## 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). **Full plain-English explainer:** https://patentbrief.org/patent/us/4531203/nand-flash-memory **Original patent:** https://patents.google.com/patent/US4531203 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Multi-Level Cell Memory Stores More Data in Less Space](https://patentbrief.org/patent/us/5903495/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. - [The Invention of the Modern Field-Effect Transistor](https://patentbrief.org/patent/us/3102230/mosfet-field-effect-transistor) — This 1960 patent describes the fundamental structure of the MOSFET, the tiny electronic switch that powers every modern computer processor. - [How Robert Dennard Invented the One-Transistor DRAM Memory Cell](https://patentbrief.org/patent/us/3387286/dram-memory-dennard) — IBM's 1967 patent for a memory cell using a single transistor and a capacitor, which became the foundation for all modern computer RAM. - [How Xilinx Chips Quickly Check If Memory Is Completely Erased](https://patentbrief.org/patent/us/5561631/high-speed-minimal-logic-self-blank-checking-method-for-programmable-logic-device) — A method for programmable chips to instantly verify that all memory cells are wiped clean using a simple, high-speed logic gate circuit. - [How Robert Noyce Invented the Modern Integrated Circuit](https://patentbrief.org/patent/us/2981877/noyce-planar-integrated-circuit) — Robert Noyce's 1959 patent for a semiconductor device that uses evaporated metal leads to connect components directly on a single silicon chip.