A ReRAM progress report

In Nuremberg, Weebit Nano was able to demonstrate its first Resistive RAM (ReRAM) product, the S130 ReRAM module, available from US fab SkyWater. The module, based on SkyWater’s 130nm CMOS process, is a big step forward in making a differentiated non-volatile memory (NVM) available for analogue/mixed signal, automotive, edge and medical applications, said the company.

ReRAM is a metal-insulator-metal structure. The metal oxide is used as an insulator. It stores data by using ions as changes in electrical resistance rather than electrons to reduce energy consumption. Unlike magnetic RAM, which can have 11 layers, ReRAM has just two, which improves yield, explains Weebit Nano’s vice-president of marketing and business development Eran Briman.

Different voltages can be applied to create a filament. With no direct interaction between radiation and the storage mechanism, ReRAM resists single-event effects and displacement damage. Being embedded between just two layers also increases security, says the company.

Testing procedures

The demo chips are being qualified and used for customer demonstrations, testing and prototyping. The company has finished testing 10K cycles at 85°C with 10K cycles at 125°C due by the middle of this year. This will be of interest to automotive semiconductor customers. Next is 100K at 105°C, says Briman.

The ReRAM technology in 130nm CMOS is low power, radiation-tolerant and secure for edge AI, for example, where Re

RAM saves neural net weights (fixed data tables), which reside in the ReRAM rather than using external NVRAM, which consumes power.

Being radiation-tolerant is relevant for aerospace and defence design, and for medical semiconductors. Weebit Nano says it is a robust memory, practical for devices such as implants, which need to be both robust and small.

With the IP commercially available for SkyWater customers, Coby Hanoch, CEO of Weebit Nano, believes: “ReRAM is no longer the technology of the future – it is here now. We are now working with a number of potential customers to map the technology’s advantages to their specific design requirements.”

Weebit ReRAM IP is an embedded module with a complete set of collateral and electronic design automation views compatible with leading design flows for SoC integration. The S130 module includes a 256-kbit ReRAM array, control logic, decoders, I/O communication elements and error-correcting code. It is designed to be scalable for customisation according to memory density, word size and system interface requirements. It is also designed with patent-pending analogue and digital smart circuitry running smart algorithms to enhance the memory array’s technical parameters.

Up to 10 years’ data retention at high temperatures can be supported. The low power consumption extends to zero at standby power with a fast access time for instant-on and quick boot-up.

Fab qualification

Full qualification of the Weebit Nano ReRAM memory module in SkyWater’s US production fab is expected to be completed in the first half of 2023. The pure-play foundry (spun out from Cypress Semiconductor) provides another source for the industry to integrate ReRAM into SoC designs. The company is talking to “most of the top 10 foundries”, according to Briman.

The Weebit ReRAM IP module in SkyWater’s 130nm CMOS process will be available with full support in the next production release of SkyWater’s S130 process design kit, once qualification is complete.

Upon request, the module is available as part of a complete subsystem including a Risc-V microcontroller, system interfaces, SRAM and peripherals.

Market potential

Yole Group estimates the embedded NVM market value will reach $3bn by 2027, and ReRAM will achieve 33% market share. The embedded ReRAM market is expected to grow from $18m in 2021 to $957m in 2027, which is a CAGR of 94%.

Looking at these figures, Briman describes a perfect storm of geo-political reasons to look for foundries outside Asia and as TSMC – which uses its own ReRAM technology – encourages others to embed ReRAM and create an ecosystem. He believes that Weebit Nano’s IP will be designed into SoCs in seven to eight months.

The interest in ReRAM’s potential in aerospace and medical applications is driving research. Weebit Nano has partnered with CEA-Leti France since 2016, using its Grenoble fab for R&D. Together, they and Nino Research Group (NRG), in the University of Florida’s Department of Materials Science and Engineering, are investigating the effects of radiation on the Weebit ReRAM module.

According to NRG founder Juan C Nino, PhD: “We know ReRAM technology to be relatively insensitive to ionising radiation, single-event effect damage, and displacement damage given there is no direct interaction between radiation and the storage mechanism of the technology. Our initial results show that Weebit ReRAM technology is very resilient to high radiation levels.”

The next stage is to test modules under a mixed radiation environment in real time at the University of Florida Training Reactor.