[HN Gopher] Inside a Ferroelectric RAM Chip
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Inside a Ferroelectric RAM Chip
Author : chmaynard
Score : 44 points
Date : 2024-09-23 20:06 UTC (2 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| kens wrote:
| Author here if anyone has questions about ferroelectric RAM...
| rwmj wrote:
| Bubble memory next please! It was the next big thing for
| storage for a brief period in the late 1980s.
| kens wrote:
| Someone gave me a board with bubble memory chips to examine,
| but when I opened up the chip it turned out to be regular
| DRAM; they were mistaken about the type of memory.
| kragen wrote:
| minor correction: the central atoms in pzt are not zircon but
| zirconium. zircon is zirconium silicate, the form in which
| zirconium is almost always found in nature. there is no
| silicate in pzt
|
| also, the atom that can substitute for zirconium in that
| central position is not lead but titanium. you do explain this
| in the following sentence, but first you say 'causes the lead
| or [zirconium] atom to physically move', which is wrong
| kens wrote:
| Thanks, I've fixed those!
| kragen wrote:
| happy to help!
| anonymousDan wrote:
| Any thoughts on how it compares to Intel Optane NVM? Also is
| there any particular material you envision as a potential
| successor for it?
| johnklos wrote:
| I've always wondered if the ROMs on my VAXstation 4000/90a are
| ferroelectric. The DEC manuals refer to it as flash ROM, but
| I've also heard / read it referred to as FRAM, although I
| couldn't say I remember where or when.
|
| But 512KB of FRAM at $3 per megabit would make that pricier
| than the machine! So I wonder what it has in it instead.
|
| Interesting! Thanks :)
| kens wrote:
| It wouldn't make sense to use FRAM for ROM, since the big
| feature of FRAM is fast write speed. I found one DEC document
| that says the Flash ROM on one product is the Intel 28F008SA,
| an 8Mb flash chip. So I expect the VAXstation uses boring
| flash too, rather than costly FRAM.
|
| Link: https://bitsavers.org/pdf/dec/semiconductor/arm/EC-
| QU5KA-TE_...
| sroussey wrote:
| What would be good for DRAM read speeds, and not care too
| much write speeds?
|
| I'm thinking of keeping an LLM's weights in a storage RAM,
| where it would be updated only every few months.
| jaygreco wrote:
| I have one! Any idea if the PZT cubes are added using the
| typical photoresist masking/etching or are they placed on die
| using some other process?
| kens wrote:
| From looking at various patents, I believe they put down a
| layer of PZT and then etch it into cubes with
| photolithography. Look at the process diagram at the bottom
| of my article, step 1128.
| throwaway81523 wrote:
| FRAM seems great and I wonder why it's not used more. TI has
| some MSP430 processors that include it, but when they went to
| the MSP432 (ARM architecture), they said something about a
| process incompatibility. Some ARM or Risc-V processors with
| FRAM would be great.
|
| Any idea what the process issue is? Would you say FRAM is on
| the decline? Super low powered CMOS ram used to also be a
| thing, but I haven't seen that in a while either.
|
| Added: article mentions flash memory is $15/gbit. I guess that
| is NOR flash? NAND is way way cheaper, more like $15/terabit.
|
| Another question: is it reasonable to say that FRAM
| automatically implements secure erasure? Like if you overwrite
| a cell, can you be sure that the old contents are gone? With
| flash, you have to worry about stuff like sector remapping
| other the covers.
|
| Here's a 4 mbit Adafruit FRAM breakout, out of stock but
| smaller sizes are available:
| https://www.adafruit.com/product/4719
|
| TI MSP430FR5969 development board: https://www.ti.com/tool/MSP-
| EXP430FR5969 That is a fancy MSP430 processor with 64KB of FRAM
| and 2KB of regular ram. The board is $16. The regular ram is I
| think a little bit faster than the FRAM and good for "infinite"
| write cycles instead of mere trillions, so I guess you need
| both. They have a few more of these boards including one with
| 128KB of FRAM if I remember right.
| kens wrote:
| The metal ions from the ferroelectric material can
| contaminate the silicon production line. I read that they
| would manufacture the silicon die at one facility (i.e. make
| the transistors) and then do the rest of the fabrication (the
| ferroelectric material, top metal, etc.) at another facility
| to avoid contamination. Maybe that's the process
| incompatibility that you mentioned. I don't know if FRAM is
| on a decline or will hold on as a niche product.
| aidenn0 wrote:
| Are the parts pin-compatible with parallel sram? I've always
| thought it would be nice to replace the battery-backed SRAM in
| old video game cartridges with MRAM or FeRAM
| jonathrg wrote:
| Texas Instruments has FRAM in some of their microcontrollers.
| It's really pleasant to use. You write to it like any other part
| of RAM, the only difference being that the bytes stay where they
| are when you lose power. With something flash you need to be more
| careful with how you use it.
| technothrasher wrote:
| I've been using it in a few projects at work as a replacement
| for flash backed serial RAM. It drops right in, as it is pin
| and function compatible with other small SPI and I2C nvram and
| eeprom chips, and isn't really much more expensive in small
| capacities.
| tonetegeatinst wrote:
| I wonder if I could sketch a single fram using klayout. Hmmmm
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