# 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. - **Patent:** US 5903495 - **Original title:** Semiconductor device and memory system - **Owner:** Toshiba Corp - **Granted:** 1999 - **Status:** Public domain (expired) - **Times cited:** 326 - **Field:** semiconductors, consumer_electronics ## What it does 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 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. ## 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. ## Real-world examples 1. NAND flash memory chips 2. Solid State Drives (SSDs) 3. SD cards and microSD cards 4. Embedded flash memory in smartphones ## Why it matters 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. ## 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. **Full plain-English explainer:** https://patentbrief.org/patent/us/5903495/semiconductor-device-and-memory-system **Original patent:** https://patents.google.com/patent/US5903495 --- _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 Flash Memory Cells Use an Erase Gate to Clear Data](https://patentbrief.org/patent/us/4531203/nand-flash-memory) — 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. - [How Buried Channel CCDs Move Data Deep Inside Silicon Chips](https://patentbrief.org/patent/us/3792322/ccd-image-sensor) — A foundational 1974 invention that improved how computer chips store and move electrical charges by keeping them away from messy surface defects. - [How Microsoft Organizes Data in Multi-Tier Storage Systems](https://patentbrief.org/patent/us/9824092/file-storage-system-including-tiers) — A method for organizing computer data into three specific tiers—log, hash, and journal stores—to make writing and reading data faster and more efficient. - [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 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.