# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DdZCrNlAklG
- **Gondola URL:** https://gondola.cc/posts/70577842-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/093b2c214f.jpg
- **Posted:** 2026-09-17T14:10:18.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

A microSD card measures 15 by 11 by 1 millimetres, weighs roughly a quarter of a gram, and can hold a terabyte. That density comes from a transistor deliberately engineered to leak.

Every bit is stored as trapped charge. A flash cell is a MOSFET with a second gate buried inside the oxide, electrically isolated on every side. To write, the controller drives the control gate to 15 or 20 volts and electrons cross a barrier roughly 7 nanometres thick by Fowler-Nordheim tunnelling, a quantum effect rather than conduction. Once through, they have nowhere to go. That trapped charge shifts the threshold voltage of the transistor, and reading a cell means measuring where the threshold now sits.

- SLC stores one bit per cell across two charge states
- TLC stores three bits across eight states
- QLC stores four bits, sixteen distinguishable levels in the same well

Modern cells hold only a few hundred electrons. Losing a few dozen can flip a bit, which is why every card runs LDPC error correction underneath.

Density no longer comes from shrinking. Planar NAND stalled near 15 nanometres, so manufacturers turned the array on its side. In 3D NAND a vertical channel is etched through a stack of alternating deposited layers, and every intersection becomes a cell in a charge-trapping silicon nitride film. Samsung shipped 24 layers in 2013. Current devices exceed 200.

The card is a package, not a chip. Bare NAND dies are thinned to around 30 micrometres, stacked in a staircase, wire bonded to a substrate beside a controller die, then encapsulated in epoxy moulding compound and laser marked. The controller is the hidden half: wear levelling, bad block mapping, error correction and the flash translation layer that disguises the fact that flash cannot overwrite in place.

Fujio Masuoka invented flash at Toshiba in 1980. SanDisk shrank it into TransFlash in 2004. The physics did not change, the packaging did.

#stemantics #nandflash #semiconductors #electricalengineering #memorytech

## Stats

- **Views:** 4,227
- **Likes:** 92
- **Shares:** 0
- **Comments:** 2

## Tags

nandflash, semiconductors, memorytech, electricalengineering, stemantics

---
Copyright (c) Gondola