​Phase change memory (PCM), with its high programming speeds and low operating voltages, is currently the front runner in the race to replace flash memory. It also offers the advantage of being more compact. But PCM is not without its drawbacks. First, it requires bulky transistor drivers located in the bottom metallization layers of the circuits. Researchers at CEA-Leti replaced the transistors—too cumbersome for new generations of chips—with smaller devices called ovonic threshold switches (OTS) connected in series to the memory. This kind of solution could make stackable PCM directly on circuits possible.

And manufacturers are already intermixing PCM with OTS for external storage solutions similar to memory sticks. But now, for the first time ever, researchers at CEA-Leti successfully co-integrated memory points into the back-end-of-line (BEOL) metallization layers deposited at the end of 28 nm fabrication processes. They also managed to place the memory points in the top layers of the circuit, preventing damage during later fabrication process steps.

The co-integration of memory and processors opens the door to solutions for new use cases that require high reliability and ultra-rapid exchanges between memory and processor. Neuromorphic chips, which mimic the human brain's behavior, and which will play a vital role in tomorrow's autonomous vehicles, are just one example. This research demonstrates the CEA's commitment to developing chips for embedded and automotive applications and making sure that Europe's chip industry thrives.