Ken ShirriffTo use the Montreal subway, you tap a paper ticket against the turnstile and it opens. But how does it work? And how can the ticket be so cheap that it's disposable? I opened up the tiny NFC chip inside to find out more... 1/15
The Montreal Métro uses this paper ticket for occasional use. The gold chip is completely fake, just printed ink. But there's a different chip hidden inside... 2/15
Underneath the paper coating, the subway ticket contains a thin plastic sheet with a foil antenna printed on it. In the lower right, the tiny black speck is the NFC chip that makes it work. 3/15
The chip is about the size of a grain of salt. I took this photo under a microscope showing the NFC chip next to some salt. The black squares in the corner are where the antenna was attached. 4/15
How does the card work without a battery? The reader sends a signal through its antenna to the card's antenna. This signal both transmits data and powers the card. The two antennas are so close that they are coupled magnetically rather than by radio. 5/15
The card doesn't transmit a signal back. Instead it changes its antenna load, causing the card to absorb more or less energy from the reader. The reader detects this "load modulation", allowing it to receive data from the card without the card using power to transmit data. 6/15
I dissolved the chip's metal and oxide layers to reveal the chip's underlying silicon, showing the layout of its transistors. 7/15
This block diagram from the datasheet shows the components of the card. The RF interface is the analog circuitry connected to the antenna. The card stores 48 bytes (the ticket info) in the EEPROM. The digital circuitry accepts commands to read and write the EEPROM. 8/15
Most of the chip is digital logic, implemented with standard-cell circuitry, but there's lots of analog circuitry to handle the antenna signal. The four bond pads are where the antenna is attached. 9/15
Many chips use standard-cell circuitry. A program converts the logic description into rows of standardized blocks (NAND gates, flip-flops, etc.) and lays out the metal wiring between them. Much faster than creating an optimized layout by hand. 10/15
The photos are a bit blurry because the chip's smallest features are about 180 nm, smaller than the wavelength of light. The box indicates 5 connected transistors; the black lines are the gates of the transistors. Today's chips are an order of magnitude smaller. 11/15
Here's a closeup of the EEPROM, which holds the chip's data, similar to a very small flash drive. (I accidentally scratched it.) The driver circuitry to access the EEPROM is to the right and below. 12/15
My first attempt at removing the protective passivation layer on top of the chip didn't work. It just thinned the layer slightly, creating these wild colors from thin-film interference. I call this die photo the "tie die". 13/15
You can buy an 8-inch silicon wafer with these chips for $9000. That sounds expensive, but a wafer holds an amazing 100,587 tiny chips. That yields a price of nine cents per chip, making them cheap enough to use in disposable tickets. 14/15
For more, see my blog post describing this chip (the MIFARE Ultralight EV1):
https://www.righto.com/2024/06/montreal-mifare-ultralight-nfc.html 15/15
https://www.righto.com/2024/06/montreal-mifare-ultralight-nfc.html 15/15
Andres Jalinton@kenshirriff
Incredible, we are in such an advance state that we create microscopic computers to be immediately disposed.
Great thread!
Incredible, we are in such an advance state that we create microscopic computers to be immediately disposed.
Great thread!
Theo Honohan@Andres It's not exactly single-use. You can put a 3-day ticket on it. Single-use items aren't really a sign of an advanced civilization, though? Maybe in the 1960s this would have seemed advanced, but in the last few decades the concomitant problem of dealing with the waste hasn't been solved. In the 60s people thought that waste disposal would be solved through technology, like everything else. It's hard to be that optimistic now.
Marsh Ray@theohonohan @Andres It’s a slip of paper with a grain of sand in it.
This is not the same category of burdensome as a plastic bottle.
This is not the same category of burdensome as a plastic bottle.
@marshray As many people have remarked in the discussion on Hacker News, it's not just a grain of sand; it's a IC, with all the manufacturing waste that goes into making one of those.
narF 😵✌️@marshray It might not seem like a lot of wasted resources if we only count the finished card... but we have to count the resources that we're used in order to produce that card in the first place. The energy, water, metal, chemicals, etc. And those are usually required in quantities that are 10 to 1000 time larger than the final product.
Like having to burn an entire tree just to make a toothpick.
@narF We can infer that the input materials and processing energy total significantly less than $0.09.
While there may be government subsidies distorting those markets to some degree, I think that gives us some idea of the magnitude of resource consumption. Probably utterly insignificant compared to the energy in the train ride it enables.
Since its function is to more reliably impose costs on the train riders, it's likely to reduce demand for rides and thus the resources spent on running the trains, it almost certainly represents a net savings of resources.
All of this is *not* to say that the system couldn't be better and we shouldn't look for ways to improve.
@marshray We know that environmental cost are often neglected in the cost of product. The cost of cleaning up after mining resources, the cost of recycling, the social cost of exploiting poor people in poor countries... All those cost aren't usually counted in the cost of a product. Especially when that product is only a few cents. 😅
Resuna@Andres @kenshirriff I think it was Robert Anton Wilson who wrote in one of his illuminatus essay collections in the '70s that in the future computers are going to be so cheap that you're going to get them in your breakfast cereal and you're going to throw them away without thinking about them.
Tristan Nitot✓@Andres @kenshirriff great thread indeed! Now I’d challenge that for a society to create computers to be immediately disposed does not mean that it’s advanced. I would call it sick, considering the impact all these kind of things on biodiversity, energy consumption, pollution and greenhouse gases emissions.
Taco Dave@Andres @kenshirriff sad in some respects as well — thinking about the scarcity of materials and what happens to waste in our society. I have mixed feelings (lol my phone tried to autocorrect “feelings” to “delusions”) because I love ephemera and keep my “disposable” tickets from visiting cities, but I’m optimistic for the future as more systems implement using your phone’s wallet system either to store the transit card or just charge you directly.
supernov@kenshirriff superb analysis one again, thank you!
Linza@kenshirriff that is really damn cool. And this is all cheaper and more environmentally sustainable than making transit fee-free?
@kenshirriff I netted some transit activists, sorry about that.
I'm genuinely interested in the manufacturing process for these. The end product is a few grams of material, so it seems like the footprint would be very small. Use phase impact as you demonstrated is nothing. I will do additional reading and hopefully return with an answer.
Magnus Ahltorp@Linza @kenshirriff This would be funny if it wasn’t so sad.
Michaela Sue@kenshirriff The very best line hidden in a footnote: "Personally, if you need a three-dimensional diagram to explain your product line, the product line may be excessively complicated." 🤣
Spectacled Langour@kenshirriff I love stuff like this, thanks!
Nathan Taylor@kenshirriff Great thread, thanks!!
(truly, il fait beau dans l'Metro)
John Gordon@kenshirriff Thank you for this. I learned things.
namelivia@kenshirriff
Thanks for the thread, this has been fascinating to read!
Thanks for the thread, this has been fascinating to read!
ꜱᴛᴇᴇʟ ʀᴀᴛ ɢᴀᴍᴇʀI know pharmaceutical companies are including RFID chips in the pills to combat fakes, skimping, and forgeries
Customers: "The cheap pills I bought were fake"
followed by "They were not our pills" after investigation by company
Jencel Panic@kenshirriff Impressive, but you can just use a barcode, duh...
Garrett Wollman@abuseofnotation You can "just use a barcode", sure, at the expense of putting another piece of hardware that has to be maintained on every bus and in every station in the system. STM used to use magstripe cards (and those readers are still on the turnstiles, just not being used). RFIDs are faster and only require one (indefinite lifetime) piece of hardware to be installed to accept all methods of payment (including phones and ordinary payment cards, although Montreal doesn't support that yet).
@wollman Our subway has one piece of hardware, which works with both barcodes and cards, greetings from Bulgaria!
I can assure you that the expense is worth it (although almost everyone use cards) --- 10c is a small price for such a piece of hardware, but it's a pretty huge if you multiply it by, say, 10000 per day.
@abuseofnotation That's *two* pieces of hardware.
@wollman It's one piece of hardware, one machine, with two different sensors, but call it as you wish (you know that there are much more than two pieces of hardware in such a machine)
Jeff ♨️ Darcy@abuseofnotation @kenshirriff I was just visiting Montreal and we used exactly these tickets. We also parked in a facility where the ticket just used a QR code. Technology is moving so fast that *several* generations often coexist within a small space.
@Obdurodon @kenshirriff A bit of offtopic, but that's a wrong way to put it. Those are not technologies of different generations, those are different technologies, each of which has its upsides and downsides.
@abuseofnotation @kenshirriff If you must, but it doesn't affect my point at all.
Sander@kenshirriff
Bruce Sterling @bruces wrote about the ubiquitous Smart Dust and objects that are more info than objects in his 2005 book Shaping Things. Succinct and succulent: https://wtf.tw/ref/sterling_shaping_things.pdf
Bruce Sterling @bruces wrote about the ubiquitous Smart Dust and objects that are more info than objects in his 2005 book Shaping Things. Succinct and succulent: https://wtf.tw/ref/sterling_shaping_things.pdf
Democracy Matters 
Wow. What an amazing labor of love. Fascinating. Thanks for doing it.
Guy who's trying his best :(@kenshirriff This is amazing work, but,
Single use, electronics, hurts, soul,
Single use, electronics, hurts, soul,
nek0@kenshirriff Thanks for this insightful thread. A truly interesting matter. I will read you blog post later.
coldclimate@kenshirriff this whole thread is tremendous
Ross Dargan@coldclimate @kenshirriff man the blog is even better. Lost too much time to this! Amazing stuff.
Václav Vančura@kenshirriff The article is amazing, thanks for that!
MatchaMakes@kenshirriff Thank you for this write up! Fantastic!
Steve Roy@kenshirriff Amazing sleuthing! I can’t help but wonder weather this is a case of it’s not because we can that we should. It’s not a lot but in volume it’s nevertheless Earth resources that ends up never being recycled?
Sue is Writing Solarpunk 🌞🌱@kenshirriff and we wonder why there are microplastics and toxic metals in everything, including us
KSev 🇳🇴🌻🚲@kenshirriff This pairs well with a recent discussion by Asiaometry on the origins of RFID.
Where Did RFID Come From?
Rich Stein (he/him)@kenshirriff
The blog and this thread are terrific. Thanks!
The blog and this thread are terrific. Thanks!
lee cyborg@kenshirriff As a Montrealer, I'm so happy to see this on your blog! I've put an OPUS card inside a jar of acetone more than once to experiment with its interior. Thanks for this!!
@kenshirriff thanks for the breakdown! A lot went over my head but I enjoyed learning what I could from it. 😅
I had an idea to try setting up a shortcut on my iPhone using one of these cards as a trigger to open my Dropbox to the folder containing photos from my trip to Montreal, and possibly see if I could do the same with cards from Chicago and Los Angeles. They didn’t seem to work, but maybe if I find a secondhand Android phone I can do something like this…
Ψ*Ψ@kenshirriff that is dirt cheap by III-V standards…I could maybe get 2 unprocessed 3”base epi wafers for that
Josh@kenshirriff TIL you can buy wafers on Digi-Key! At first I was surprised by your $9k figure for an 8-inch wafer on 180nm, but that makes sense for a distributor like Digi-Key.
Thanks for the awesome teardown and analysis!!
Lumi Akimova@kenshirriff
Wow!! 9 cents for the chip only sounds incredibly expensive!
As a reference, the current price of metro ticket in Tashkent is ~13 cents. And single use tickets are just a piece of thermal paper with QR code (RF cards and even normal credit cards are also supported)
As another reference, I've seen estimation of 11 cents per RP2040 chip: 20k chips per wafer, $2300 per 40nm TSMC wafer
MicroBlog Castellano@lumi @kenshirriff Here in Madrid, single use tickets disappeared. They were replaced with multi-use cards. It sounds good, but these cards are expensive (compared to the 2-euro train card), and they broke easily.
jarek@lumi @kenshirriff Montréal's L'Occasionnelle single-ride ticket detailed by Ken here costs 3.75 CAD, so 0.09 CAD (or even 0.09 USD) isn't that much - Canadian fare collection costs are frequently on the order of 5-10% of the fare cost, so the chip card fits within that.
Multiple-use tickets have significant discounts in Montréal, so they are used for most trips. The single-use tickets are for very occasional riders, or if you left your main card at home or something.
Yeah, I'm sure with Canada prices even $0.09 for the chip only might make sense :)
mirabilos@lumi @kenshirriff Tashkent sounds really progressive (and I mean that honestly)
Yeah! But I'd prefer the single-use ticket to be a reusable fare token. Like they do in Almaty
@lumi @kenshirriff of course, but what if you’re really just passing through a bit, better have paper than plastic with metal and microchips then.
Fare token as in "coin you drop into a station gate" :)
@lumi @kenshirriff nah, requires you to have coin at hand, hard to get chance, would take too long at a chokepoint, impossible to buy in advanc, requires gates as opposed to possible
manual control
manual control
Axel Rauschmayer@kenshirriff The tech is amazing but it still seems wasteful (not w.r.t. money but w.r.t. resources). (E.g.) QR codes would be better but maybe they don’t work for this use case(?)
Mike Szczys@rauschma @kenshirriff I think you're right, but I also think you could buy one ticket and reproduce the QR code with a smartphone (take photo, display on screen).
This NFC approach doesn't need to be strong security, just enough of a barrier to make it non-easy to copy.
@szczys Right. You’d need a central database to prevent the same ticket being used multiple times. That could indeed be a deal-breaker.