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Inside a Ferroelectric RAM Chip
- RecycledEle 2y agoBut it costs $500 to $1,000 per GB?
- kens 2y agoAuthor here if anyone has questions about ferroelectric RAM...
- hulitu 2y agoDoes it held its content during a BCI test ?
- rwmj 2y agoBubble memory next please! It was the next big thing for storage for a brief period in the late 1980s.
- kens 2y agoSomeone 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.
- kjs3 2y agoWhich 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. :-)
- MBCook 2y agoOh 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.
- kragen 2y agobubble memory is years after core, and dram is a great deal more complicated than you are imagining
- dfox 2y agoThere 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.
- kragen 2y agothe 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
- MBCook 2y agoI 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.
- physicsguy 2y agoI 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).
- kragen 2y agominor 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
- anonymousDan 2y agoAny thoughts on how it compares to Intel Optane NVM? Also is there any particular material you envision as a potential successor for it?
- johnklos 2y agoI'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 2y agoIt 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_SA110_Evaluation_Board_Reference_Manual_199603.pdf https://bitsavers.org/pdf/dec/semiconductor/arm/EC-QU5KA-TE_...
- jaygreco 2y agoI 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 2y agoFrom 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 2y agoFRAM 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 https://www.adafruit.com/product/4719 TI MSP430FR5969 development board: https://www.ti.com/tool/MSP-EXP430FR5969 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 2y agoThe 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.
- cushychicken 2y agoIt’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.
- aidenn0 2y agoAre 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
- kens 2y agoThe 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.
- aidenn0 2y agoThe 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.
- polpo 2y agoI’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.
- rbanffy 2y agoWon’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.
- formerly_proven 2y ago>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.
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- alnwlsn 2y agoWell 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?
- kens 2y agoThere 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.
- jonathrg 2y agoTexas 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 2y agoI'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.
- beeflet 2y agoWhat is the latency like vs DRAM?
- polpo 2y agoIn my experience with parallel FRAM, it’s as fast as SRAM and is a drop in replacement with the same timing. A lot of folks have replaced battery backed SRAM with FRAM on game consoles.
- beeflet 2y agoHoly cow thats cool. So It's like an expensive nonvolatile replacement for volatile memory. I wonder if in the future there could be computers with no sense of "memory vs storage", that it would all just be a single contiguous "memory". Instead of turning off the computer and hibernating, you just turn off the LCD backlight and the IO.
- grishka 2y agoYou would still need to turn the CPU off though. Or do you suggest replacing the registers and caches and all other volatile memory with this stuff?
- tonetegeatinst 2y agoI wonder if I could sketch a single fram using klayout. Hmmmm
- Brian_K_White 2y agoI've been using MRAM instead as soon as I read that the way FRAM works internally is that every read is actually destructive and but written right back after the read. I don't want that in something that's meant to replace a mask rom.
- therein 2y agoI remember there being some document in which TI describes how this is done atomically at a physical level so there is no way that you can end up losing power and having the read-triggered write fail to complete.
- rpaddock 2y agoI designed in a Everspin MRAM. Had to take it back out when we learned that the small magnet, to activate a reed switch, near the MRAM would destroy it. It did not just lose a few bits, the device was forever dead. We are talking Refrigerator Magnet level field in close proximity. Great technology as long as no magnetic fields are close to the device.
- Brian_K_White 2y agoOk in looking into this for https://github.com/bkw777/WP-2_IC-Card?tab=readme-ov-file#m-ram-512k-card https://github.com/bkw777/WP-2_IC-Card?tab=readme-ov-file#m-... Everspin claims to be internally shielded for between 25 to 125 gauss depending on the temperature rating and package type (pdf included above). In my case using the parallel interface and TSOP-II package, the Industrial version is the best and is supposed to resist up to 125 gauss. And a fridge magnet is around 100 gauss (obviously they vary widely but I found a random chart that placed fridge magnet at 100). Also magnetic fields drop off with an inverse-cube law so even a small distance drastically weakens the field. So in many applications with a chip inside of some product like a vintage computer, the chip is likely to be at least an inch away from any exterior surface, and often a magnet or coil will also be inside of some other enclosure like a speaker, adding yet more inches of distance. So even the commercial version at only 25 gauss shielding is probably fine in most cases. In my application above it's a thin card with essentially no distance from the exterior to the chip, so any bare exposed magnets like a fridge magnet, or the pretty strong magnet in the base of a flash light right on my desk here, can easily come to within 1mm from the chip. If the shielding claims are true then at 125 gauss the card should be ok even with a mild magnet laying right on the card. Setting on top of something like a speaker should be fine since the speaker magnet is suspended in the center of a box. But I still have to generally avoid magnets or electromagnets. Maybe it can stand up to my fridge magnets, but that flashlight is quite a bit stronger. If you are designing a pcb and can make changes and have room, a common steel rf shield should help a lot as long as it's made of mostly iron or nickel. mu-metal is best but a common plain steel shield should be almost as good since steel is mostly iron. They do sell them in generic form not just custom made: https://www.digikey.com/short/zm42wjmc https://www.digikey.com/short/zm42wjmc
- heironimus 2y agoThese saved me from a redesign 25 years ago. I had an 8051 with 256 bytes of RAM and a serial EEPROM with limited writes. Replacing the EEPROM with a serial FRAM allowed me to increase the effective RAM. I had to do some tweaking and figuring because it was so much slower. Also, FRAMs had limited writes AND reads, but on the order of billions instead of millions. Billions of reads are a lot, but you still had to be careful.
- djmips 2y agoJust musing around the word Ferroelectric, I was expecting perhaps something related to iron in the PZT but it's lead, zirconium, titanium, and oxygen. So I learned that Ferromagnetic simply means "iron-like magnetic" and that ferroelectric was coined by analogy to the hysterisis curve of ferromagnets in a magnetic field (MH curve) but in ferroelectric it's an electric field (P-E curve).
- anovikov 2y agoSo it's like magnetic core memory, miniaturised to fit into a chip?
- kens 2y agoFRAM is like magnetic core memory in many ways, but the underlying principle is completely different: it is ferroelectric rather than ferromagnetic. And the materials are completely different.