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Comment by kens | Hacker News Reader

Author here if anyone has questions about ferroelectric RAM...

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.

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.

It’s real popular in the niches that use it. Industrial controls systems really seem to love it.

I’ve heard that some real fast control systems like to have it as a recovery method to save state in event of major system hiccups.

It's also a pretty good debug tool: you can log a trace into a circular buffer in it more or less continuously, then dunno or the contents after a crash or some other failure.

Hmm, thanks, I'm surprised those MSP430 cpus aren't more expensive if their fabrication is that complicated. So it sounds like the ARM designs (I guess basically hard macros from ARM Ltd.?) aren't compatible with that type of process. I wonder if a RISC-V design starting with downloaded HDL would be easier. I hope it happens: FRAM is really cool in concept and I've had a few application ideas where it would be great.

I've been wondering if the MSP430's are a single die with the FRAM and the µC on the same process, or if they're co-packaging a "standard" FRAM die made elsewhere.

If the FRAM was a separate die, they could use any CPU they wanted instead of being limited to the MSP430.

Added: aha, found the fancier ($20) Launchpad that has 128KB of FRAM and an LCD display:

https://www.ti.com/tool/MSP-EXP430FR6989

This thing was apparently released in 2014. Technology continues to march backwards.

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

Thanks, I've fixed those!

happy to help!

Bubble memory next please! It was the next big thing for storage for a brief period in the late 1980s.

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.

Which bubble "chips" would someone confuse with dram? All the Intel, TI, Hitachi and Russian ones I've ever seen are relatively large, square, thick and decidedly un-DRAM like.

I have several working bubble memory boards. You can't take them apart. :-)

This was an IBM board so all the chips were in large, square, metal packages. These packages are descendants of the SLT modules used in the System/360.

Ah...that makes complete sense. The SLT chips are certainly bubblememory-ish.

Oh wow I’d never heard of bubble memory before. That’s crazy.

The (in retrospect) strange and complicated things people came up with to store bits before magnetic core got popular and then later silicon wiped the field are so much more interesting than what we’ve got now.

I get why silicon won. But it’s just nowhere near as fun as bubble memory, delay lines, or CRTs.

bubble memory is years after core, and dram is a great deal more complicated than you are imagining

I know. I saw the bubble memory was used in the 70s and maybe even 80s, which is long after the days of core memory being becoming common.

And I know DRAM isn’t exactly simple.

But it just doesn’t feel as neat to me as pushing bubbles around or using a transducer to put a wave through mercury or other delay line. Or drawing a “picture of memory” for no one on a CRT because that _is_ your memory.

If one of those had won and was what everyone was used to, I’m probably think they were old hat and DRAM was crazy and cool. But that’s not how history worked out.

There is not that much complexity (circuit-wise) in the DRAM array itself apart from the fact that the sense amplifier is essentially an SRAM cell and not really an “amplifier”. Another layer of ridiculous complexity is how to interface that to the outside world without spending the precious die area of DRAM optimized process for complex interface logic or PHYs, so you get the only high-speed single ended parallel bus with weird voltage levels interface that is used in modern computers.

the dram array is pretty simple, it's true, but its behavior isn't, and the circuitry around the edges to make it act like ram isn't. you have the sense amplifiers with their inputs that are also their outputs, yeah, but also precharge, refresh, and stuff i'm not privy to

I did my PhD on a purported successor to this - rather than using magnetic bubbles the idea was to use things called Skyrmions which emerge naturally in some materials as either information carriers or to store data in place. In practice it’s never really been taken up by industry for a few different reasons (density, can’t move the skyrmions in a straight line with a current, difficult to read whether one exists or not in a specific place).

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 :)

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_...

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.

DRAM or SLC NAND. Be careful with read-induced disturbance on the latter, though.

Well I guess we know what happened to those failed chips from Curiousmarc's broken DRO.

Maybe I missed it, but what actually makes it wear out? And why does it last so much longer than flash/eeprom?

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.

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

The FM1808B and FM1608B might work for you. These are 32Kx8 and 8K×8 FRAM chips with standard SRAM pinouts, in DIP packages. If you don't need a DIP, you have a lot more choices.

The SOIC look like they could work as-is in a gameboy, which (thanks to Pokemon) is the most common request for replacing batteries. The DIPs could be made to work in most NES games too, I suspect.

I’ve replaced battery backed SRAM in several game consoles and other devices with FRAM (Neo Geo CD, Sega Saturn, an HP oscilloscope) and for some it’s drop-in, and in a few you have to bodge some lines.

Won’t that negatively impact the life expectancy of the device? FRAM is rated for trillions of reads and, if the SRAM is frequently read, a trillion reads isn’t that much.

>100 trillion reads per location over 30 years still means you gotta read locations at over 100 kHz 24/7. Not good enough for main memory, sufficient even for frequently accessed configuration values.

Definitely not for running code directly from it (unless it's shadowed to RAM), but for storing config data or checkpoints, it makes sense.

I guess it depends on whether the game cartridges only use it for storing savegames, or as actual additional RAM.

Yes. It'd be a problem for running code directly from it - it'd be better to cache it to DRAM so that all reads would come from DRAM and only writes would make it to FE-RAM.

IIRC, it was a common trick with 286 and 386 PCs, because BIOS ROMs were 8-bit wide and shadowing the BIOS in RAM made it much faster.

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?

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.

Any thoughts on how it compares to Intel Optane NVM? Also is there any particular material you envision as a potential successor for it?

Does it held its content during a BCI test ?

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