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.

What it 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 it doesn't 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.

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.

Real-world examples

• 1.USB flash drives
• 2.Solid State Drives (SSDs)
• 3.MicroSD cards
• 4.Smartphone internal storage