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.

What it covers

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 doesn't 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.

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.

Real-world examples

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