In June 2010, SanDisk announced it had shipped a “new” product — the WORM SD card — to a Japanese police force. The concept is well known to any of us who were around computers at the time optical disks were being developed since they were first known under the same moniker of write once, read many times. The SanDisk WORM SD card was not a disk per se but rather an integrated circuit memory chip that could perform the function. Immediately, I wondered if this was related to SanDisk's acquisition a few years earlier of Matrix Semiconductor. When I first heard about Matrix memory technology, I thought it would make a great archival digital film.
Shortly after the SanDisk acquisition in 2005, I posted some thoughts about the deal on the corporate blog I created for Semiconductor Insights (unfortunately, I cannot provide a link since the company has darkened that blog site). There was an announcement that SanDisk was re-engineering the Matrix technology to be re-writable.
It's bizarre to think that it would be possible to convert essentially a blown fuse (more precisely, anti-fuse, but still that is the essence of how any type of one-time programmable or OTP memory works) into a re-writable memory. But that’s what SanDisk CFO, Judy Bruner, seemed to imply in her EE Times quote:
"We would have 3-bits per cell, 4-bits per cell and three-dimensional memory which we acquired through our acquisition earlier this year of Matrix Semiconductor and which we are busy at work looking at how we evolve that 3D technology from a one-time-programmable to a read-writable type of memory ."
Either there was serious confusion about the core Matrix Semiconductor technology, or SanDisk was using the acquisition buzz to promote one of their own developments that was connected in some way to the stackable or three dimensional concept of Matrix OTP. Perhaps there was even a patent related to 3D memory that SanDisk needed from the Matrix IP pool, but I am confident that the any new re-writable memory — 3D or otherwise — would not be using the original Matrix storage element.
I thought it would be prudent to check with SanDisk about the lineage of the new WORM cards. This is what was returned:
"The new SanDisk SD WORM cards use proprietary SanDisk memory technology that allows us to achieve this archival length."
With that kind of help, I’m sticking to my original thesis.
If you want more insight into the OTP anti-fuse memory, you can look at US patent application 10027466 . Even a quick skim of this application should be enough to convince you of just how robust this type of memory is after writing to it.
It now appears that SanDisk has gave up on the alchemy of converting OTP memory into a re-writable form as the Bruner quote suggested. It seemed SanDisk finally decided to take advantage of one of the true merits of the Matrix 3D memory technology. As it was touted for police departments, the impossibility of deleting or altering original files made the WORM SD card a perfect fit for acquiring and storing photographic evidence.
The engineers at Matrix Semiconductor created a stackable cross-point fusible memory that could be manufactured on mature or even trailing edge fab lines and still produce very dense packing of bits. The extreme regularity of the bit cell meant that the memory pitch could be much better than the standard pitches allowed in the design rules of the technology. On top of that (literally) the memory cells could be stacked layer upon layer for many times higher cell packing per square millimeter of silicon. The cost per bit was very low.
I had the chance to interview the Matrix CTO in the days before the acquisition for the Insight Award program that Semiconductor Insights was launching. I was sold on both the talent and the technology Matrix had developed. So it was no surprise when they became an acquisition target for SanDisk.
Unfortunately, it seemed to become yet another case of a mature company where the decision makers are unable to see beyond the technology or lines of business that have been historically successful. SanDisk announced that the Matrix 3D memory was being transformed into a traditional re-writable form, and it appeared they were mired inside some deep wheel ruts cut by the NAND flash business. Or maybe they were just swallowing up a possible competitor.
Both re-writable flash and OTP memory are non-volatile. What distinguishes the OTP is just how non-volatile it is. That's what makes it attractive as a data archive. It is in no way unflattering to police departments to say that many professional as well as amateur photographers take the safety of their digital image files just as much if not more seriously than the justice system. That's why I think police archives are just a way of rolling out the technology.
It's great marketing to convince us that our own precious memories will be around for our grandchildren to enjoy if kept on the SanDisk SD WORM card. None of the usual enemies of data storage media like charge leakage or exposure to radiation or magnetic fields can change the memory state of the memory developed by Matrix Semiconductor. Alas, fire and flood are still the enemies of your family photo collection, but even a modest attempt to protect the digital film would keep those photos safer longer than old fashioned silver-halide film or paper prints.
But it didn’t take Japan’s national police force to convince me. Based on the Matrix 3D memory's potential for mass producing cheap digital film, the convenience factor was enough for me. Think about it. Take the pictures then upload them to your PC or wherever you like. Fill your SD WORM card and put it on the shelf. Now you have your pictures where you intend to view and use them, and they are already backed up on a dependable storage system. Back-up is built in automatically.
But then again, maybe I'm just another dinosaur that remembers buying analog film where we measured it by exposures or even by the foot. At one time, that concept was deeply enough ingrained that even the flash manufacturers (and most notably SanDisk themselves) believed they might market "digital film" as a consumable the same way that Kodak brought photography to the mass market.
Hopefully, SanDisk hasn't waited so long that the average consumer has realized the importance of data back-up and taken to other forms like cloud computing.