NAND Flash Memory,
Born on the Eve of
the Spread of the Internet
--First, let’s do a simple review of flash memory, first created by KIOXIA (formerly Toshiba).
Yamaji : Flash memory is an “extremely small storage device utilizing a semiconductor,” and is incorporated into familiar items such as smartphones, tablet computers, video cameras, and game machines. USB memory, which we use regularly to transfer data, also uses flash memory. Toshiba created the world’s first NOR flash memory in 1984, and in 1987, it invented NAND flash memory, which is widely used still today.
-Not only had the Internet not yet spread in 1984; but computers were also not yet widely used. Computers, costing as much as a small car, had at last become usable for word processing and spreadsheet calculations. However, they couldn’t handle video and audio as the data was too large. Released that year, the memory of the Apple Macintosh was 128KB, and around that time Bill Gates said, “If a computer has 640KB of memory, it’s enough.” Flash memory is technology that was born at the dawn of the IT age.
Yamaji : Yes, it was invented by former Toshiba researcher Dr. Fujio Masuoka. At the time, tape and disks were the mainstream as storage devices that did not require a power source (non-volatile memory). However, storage device using magnetism had drawbacks such as long read / write times and bulky sizes.
--Was flash memory developed through efforts to overcome these weaknesses?
Yamaji: Yes, that’s exactly right. Dr. Masuoka was convinced that “Using flash memory, people will be able to carry dozens of songs and listen to them while running.” Around that time, portable cassette players had spread, and future digital portable music players expected to come. However, in terms of design, it was difficult to create a large-capacity NOR flash memory. The issue was how to enlarge storage capacity while retaining a compact size.
The conclusion we finally arrived at was that NAND flash memory had a smaller circuit scale and was more amenable to storage capacity expansion than NOR flash memory. Operating principles were announced in 1987, and Toshiba was the first to commercialize. Today, this is the type of flash memory that is most prevalent.
--How does flash memory work?
Yamaji: Flash memory stores information by holding electrons in parts called memory cells, which exist in innumerable quantities on the integrated circuit chip. It stores information based on the presence or absence of electrons through either holding or discharging.
Think of it as the chip being the land and the cell being the home. It’s like increasing the number of homes on a piece of land of a fixed size—the more memory cells there are, the more information that can be stored.
NAND flash memory is a breakthrough invention that made enlarging storage capacity possible without increasing chip size, simply based on ingenuity. Subsequent research and development efforts were focused on the downsizing of cells to enable the storage of more information. And the enlargement of storage capacity proceeded at a pace surpassing that outlined in Moore’s Law.
*Moore’s Law: Put forward by Gordon Moore, one of the founders of Intel, in 1965. And an updated principle states: "The number of transistors incorporated in a chip will approximately double every 18 months.”
Applying an updated Moore’s Law to the flash memory semiconductors, capacity based on chip size doubles every 18 months. This means, a fourfold increase in three years, and about 100 times in 10 years. Stated another way, the price in terms of capacity decreases to about 1/100 over 10 years.
The density of the NAND increased at a pace surpassing Moore’s Law through technology such as grating, in addition to miniaturization. A basic NAND flash memory stores 1 bit based on the presence or absence of electrons in a single cell, but by subdividing the electronic state within a cell, grating technology enables the storage of 2 bits or more. I’ll spare you a detailed explanation for now, but at the end of the day it means that more than twice the amount of information can be stored in the same space.