The technology that has made it possible to reach this milestone has been in process for almost a decade, as ARM has been waiting for the manufacturing methods that would allow them to create a fully functional core made of plastic. Now the company already has something tangible and it works, so they have published the first results of their research in the journal Nature.
How to create a CPU made of plastic?
“Plastic” or flexible electronics have been around for a long time, and usually involve large but simple designs for the electronics stream or basic 8-bit adders. What we’re seeing now is something a little different: the key news is that ARM, in partnership with PragmatIC, has produced a fully functional silicon-free version of one of the ODM’s most popular microcontrollers, the M0.
This M0 core sits right at the bottom of the stack of products from ARM core, and yet its minimalist design is very popular for silicon processors due to the very small area required for its matrix and its low power requirements. So while this CPU won’t power your next great device any time soon, many of the onboard electronics you own likely already rely on M0 cores for fundamental control tasks.
PlasticArm, as they have dubbed it, recreates the M0 core in a flexible plastic medium. This is important for two factors: first for the ability to enable processors or microcontrollers in something other than silicon, since it will allow certain programming on the packaging. Together with a particle sensor, for example, it could allow food packaging to determine when what’s inside is unfit for consumption due to spoilage or contamination. The second factor is cost, with flexible processing at scale being orders of magnitude cheaper than equivalent silicon designs.
To ARM’s credit, the new M0 design is reported to be 12 times more powerful than current state-of-the-art plastic computing designs.
Plastic M0 Core Details
In ARM’s press release, the company states that the PlasticArm M0 design has 128 bytes of RAM Y 456 bytes of ROM, while also supporting a micro architecture 32-bit ARM. Within the article and research published in Nature, we obtain more specific details about it:
The processor is constructed of a polyamide substrate and is formed through thin-film metal oxide transistors, just like IGZO displays. This means that it is technically still a photolithography process using spin coating and photoresist techniques, and the processor has 13 layers of material and 4 layers of routable metal. However, since TFT designs have become widespread since the use of IGZO displays, the manufacturing cost is quite low.
The kernel supports ARMv6-M architecture with a 16-bit ISA combined with a 32-bit subset. As with normal M0, the data bandwidths and addressing are 32-bit, the layout in order is a two-stage pipeline, and the kernel supports up to 86 instructions. The main difference with the silicon M0 core is that the log file, instead of being inside the CPU, is assigned to the 128-byte bank of DRAM (despite this the plastic M0 core is compatible with all the others Cortex M0 cores).
A typical die size for a Silicon Cortex M0 using TSMC’s 90nm process is 0.04mm2, while PlasticArm uses an 800nm equivalent TFT process and the core size is 59.2mm square (7.536 x 7.856 mm). This makes this plastic CPU approximately 1,500 times larger than the size of a standard IoT implementation; The other big difference is found in the frequency, since according to the source article the Plastic M0 works at 20-29 kilohertz with a 3V input (an M0 in a 180 nm process can work at 50 MHz). It is a frequency difference of 1600-2500x.