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Ken Shirriff

To make a capacitor, each PZT cube has a platinum plate line underneath and a platinum plate contact on top. The plate lines are the shiny vertical white rectangles in this photo. At the bottom, large transistors drive the selected plate line positive or negative.

A closeup die photo showing some of the storage capacitors on top of the plate lines. Most of the photo is taken up by the large transistors connected to the plate lines.
23 September at 19:02 | Open on oldbytes.space
6 comments
Ken Shirriff

Here's a closeup of the part number and Ramtron logo on the die.

Microscopic text on the die: FM24C64A Ramtron.
23 September at 19:03 | Open on oldbytes.space
Ken Shirriff

To learn more about this FRAM chip, see my blog post: righto.com/2024/09/ramtron-fer
Thanks to CurousMarc for supplying the chip.

23 September at 19:04 | Open on oldbytes.space
bitsavers.org

@kenshirriff

why do they have finite r/w lifetimes?

23 September at 19:23 | Open on oldbytes.space
Ken Shirriff

@bitsavers There are multiple factors that limit the number of writes that FRAMs can handle: changes in crystal structure as Ti ions replace O, mobile ions collecting at grain boundaries, and something to do with 90º domains.

23 September at 19:41 | Open on oldbytes.space
F4GRX Sébastien

@kenshirriff @bitsavers it's not really infinite since the endurance was probably reached in Marc's DRO. The fram was used by the readout to give the illusion of an absolute scale, but I believe the integrated fram that failed was updated too often (maybe every scale tick).

23 September at 19:53 | Open on chaos.social
gudenau

@kenshirriff Oh it's almost like microscopic core memory? Pretty neat stuff.

23 September at 19:40 | Open on fosstodon.org
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