# How Robert Dennard Invented the One-Transistor DRAM Memory Cell

> IBM's 1967 patent for a memory cell using a single transistor and a capacitor, which became the foundation for all modern computer RAM.

- **Patent:** US 3387286
- **Original title:** Field-effect transistor memory
- **Owner:** International Business Machines Corp
- **Granted:** 1968
- **Status:** Public domain (expired)
- **Times cited:** 191
- **Field:** semiconductors, consumer_electronics, computing

## What it does

This patent describes a memory cell that stores a single bit of data using only one field-effect transistor and one capacitor. Before this, computer memory required multiple transistors per bit, which made it bulky, expensive, and power-hungry. By shrinking the design to a single transistor, this invention allowed engineers to pack millions of bits of data into a tiny silicon chip. When the transistor is activated, it allows a charge to be stored in the capacitor, representing a one or zero.

## What it does NOT cover

- Does not cover static RAM (SRAM) which uses multiple transistors to hold data without needing periodic refreshing.
- Does not cover the manufacturing processes for etching these transistors onto silicon wafers.
- Does not cover magnetic core memory or other non-semiconductor storage technologies.

## The clever bit

By realizing that a capacitor could hold a charge for long enough to be useful if refreshed periodically, Dennard eliminated the need for complex, multi-transistor flip-flop circuits for every single bit of storage.

## Real-world examples

1. DDR4 and DDR5 RAM sticks in desktop PCs
2. LPDDR memory modules in smartphones
3. Embedded DRAM in gaming consoles

## Why it matters

This invention is the reason your computer or smartphone can have gigabytes of memory. It enabled the transition from room-sized computers to the personal computing era by making high-density memory affordable and reliable. It remains the standard architecture for Dynamic Random Access Memory (DRAM) used in almost every electronic device today.

## Frequently asked questions

### What does How Robert Dennard Invented the One-Transistor DRAM Memory Cell cover?

IBM's 1967 patent for a memory cell using a single transistor and a capacitor, which became the foundation for all modern computer RAM.

### Who owns patent US 3387286?

International Business Machines Corp owns this patent, granted in 1968.

### 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 3387286 cited by?

This patent has been cited by 191 later patents that build on its ideas.

### What problem does this patent solve?

This invention is the reason your computer or smartphone can have gigabytes of memory. It enabled the transition from room-sized computers to the personal computing era by making high-density memory affordable and reliable. It remains the standard architecture for Dynamic Random Access Memory (DRAM) used in almost every electronic device today.

### What does this patent NOT cover?

Does not cover static RAM (SRAM) which uses multiple transistors to hold data without needing periodic refreshing.

**Full plain-English explainer:** https://patentbrief.org/patent/us/3387286/dram-memory-dennard

**Original patent:** https://patents.google.com/patent/US3387286

---

_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:

- [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 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 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 Transistor](https://patentbrief.org/patent/us/2524035/point-contact-transistor) — Bell Labs' 1950 patent for the point-contact transistor, the fundamental electronic component that makes all modern computing possible.
- [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.