ST microcontrollers go to 18nm FDSOI with phase-change memory

News | March 19, 2024

By Peter Clarke

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STMicroelectronics NV has announced the commercial introduction of a chip manufacturing process based on 18nm fully-depleted silicon-on-insulator (FDSOI) with embedded phase-change memory (PCM).

The first STM32 microcontrollers based on 18nm FDSOI will start sampling to selected customers in 2H24, with production planned for 2H25, ST said.

The process was co-developed with Samsung Foundry and will be used for next-generation embedded processing devices in industrial, communications and healthcare applications. The first microcontroller based on this technology will integrate the most advanced ARM Cortex-M core with enhanced performance for machine learning and DSP.

As well as using Samsung Foundry as a source of chips STMicroelectronics will run the process in European fabs in volume, Remi El-Ouazzane, president of the microcontrollers, digital ICs and RF business unit at ST, said.

When asked whether Samsung Foundry would be free to supply the 18nm process to other customers, El-Ouazzane said it has not yet been disclosed whether Samsung Foundry will be free to offer 18nm FDSOI.

Adoption of 18nm FDSOI with embedded PCM brings an up lift in performance and energy efficiency for embedded processing applications while allowing larger memory sizes and higher levels of integration of analog and digital peripherals, the company said.

The manufacturing process is capable of 3V operation to supply analog features such as power management, reset systems, clock sources and digital/analog converters and is the only sub-20nm process capable of this, ST claimed.

Flash don’t scale

So far ST’s leading STM32 microcontrollers have been based on 40nm CMOS and made use of flash memory for embedded non-volatile memory but flash has problems scaling below 40nm partly due to the large memory cell size and the die area occupied by charge pumps to implement high voltages.

Other companies and foundries have embraced the use of magnetic RAM and metal-oxide based resistive RAM as embedded memories for SoCs. However ST has perserved with phase-change memory research decades. The company has already introduced embedded PCM for automotive and aerospace applications on 28nm FDSOI (see ST samples embedded phase change memory for automotive applications).

But progress has continued to be painstaking and the migration to 18nm has been in development for some time. Researchers from Samsung and ST reported on the 18nm FDSOI technology logic platform with embedded phase change memory at the IEDM conference in December 2021 (see Samsung, ST report phase-change memory on 18nm FDSOI).

Ricardo De-Sa-Earp, executive vice president responsible for general-purpose microcontrollers said: “Now we are going to PCM for industrial STM32 microcontrollers.” He added the process overall brings a up to a 50 percent better performance-to-power ratio with much denser non-volatile memory and 3dB improvement in RF noise figure.

Thermal resilience

PCM has not been widely adopted across the electronics industry. The same basic technology, phase change in compounds of germanium antimony and tellurium. It was the basis for Intel’s now-failed 3D XPoint storage memory technology. It has acquired a reputation of being susceptible to temperature and thermal cross-talk errors because memory cells operate on the thermally-triggered change of phase between amorphous and crystalline states with different resistivities.

However, ST has championed the use of PCM and research into proprietary material mixes may have provided ST with a material that is thermally robust across automotive and aerospace temperature ranges and therefore also across the industrial temperature range.

ST executives declined to say exactly what type of selector device is used in its PCM arrays. “We are able to use a mono-directional selector which allows the PCM to be very efficient in terms of density and reliability,” said El-Ouazzane.

When asked about STMicroelectronics ability to supply in volume from its own fabs El-Ouazzane, commented that having to manufacture in multiple locations to support local supply-chain resilience is sub-optimal, but is something that ST is ready to support.

“The 18nm process is a big deal. It is going to amplify the lead ST has with STM32 microcontrollers in the decade to come,” El-Ouazzane said.