Weebit moves ReRAM on to ‘secret-sauce’ materials
Weebit Nano Ltd. has expanded its position from the use of ‘pure’ silicon-oxide as the basis for its non-volatile resistive RAM technology.
Silicon oxide is a well-characterized material. Its use by Weebit produced good results across a range of parameters. It was also a point of differentiation from other non-volatile ReRAM developers that have focused on the use of transition-metal oxides or phase change materials, such as chalcogenide glass.
A company spokesperson said: “Weebit’s technology was founded on SiOx, but over time the company has expanded to use other fab-friendly materials and compositions. While we aren’t sharing the specific recipe publicly – we’ve stopped mentioning the specific materials in our communications – the company’s focus remains on easy manufacturability with fab-friendly materials. This was and continues to be a cornerstone of the business.”
The company was launched back in 2014 on the basis of work by Professor James Tour at Rice University. Professor Tour had shown thin films made of nanoporous silicon oxide – a mix of silicon dioxide and silicon monoxide – could be made to switch resistance states with a high on-off ratio.
This was a somewhat surprising but potentially useful result as silicon dioxide had been used as a primary insulating layer in integrated circuits for many years. It was therefore the ultimate fab-friendly material.
Weebit’s spokeperson described the changes that have been made by Weebit as “a minor tweak.” The spokesperson added: “Weebit is still 100 percent committed to oxide materials. As part of developing the technology, the company realized that modifying the composition so it is not pure SiOx leads to better results. We prefer not to make the exact composition public as it’s considered part of the secret sauce.”
It could be that Weebit Nano has adopted or adapted technology from French research institute CEA-Leti (Grenoble, France). Weebit has been working with CEA-Leti as a research partner for many years.
Leti has its own take on ReRAM that it calls OxRAM. This was originally based on titanium-doped hafnium oxide active layers. It is thought that like many other resistive RAM (ReRAM) technologies OxRAM is based on metal ion and oxygen vacancy migration to make and break a filamentary conduction path in a memory cell.
In October 2021 the Minatec research group announced that 16kbit OxRAM arrays had been made on 28nm FDSOI wafers. Minatec said that the introduction of “a tiny amount of silicon into the active metal (hafnium oxide) is an innovation that makes it possible to use a lower voltage, which is easier on the 28nm transistors closest to the memory.
Silicon dioxide is still used as the insulator in the back-end of line (BEOL) in advanced ICs. But for leading-edge transistors down at the silicon surface hafnium oxide is used for its higher dielectric constant.
Intel introduced hafnium oxides to IC manufacture in 2007 as a replacement for silicon oxide as the gate insulator in field-effect transistors in its 45nm manufacturing process. Chip manufacturers have followed suit at similar nodes and below. The high-k dielectric layer in ICs may now be twin layers of hafnium dioxide and silicon dioxide; may be described as hafnium silicate and may include titanium and described as hafnium titanate.
With atomically thin layers what constitutes a compound and what a dopant can be become hard to distinguish.
It would make sense for Weebit to “tweak” ReRAM so that it can be made either in the BEOL or from the hafnium oxide systems in use near to the silicon surface of an advanced IC. However, could this be at the loss of some its intellectual property advantage and differentiation?
CEA-Leti has filed patents on its OxRAM research and is reportedly in talks with multiple potential manufacturers.
There is also the engineering issue of how Weebit’s more advanced 28nm and 22nm FDSOI ReRAMs, presumably manufactured on the secret material recipe, perform across the broad range of parameters.
At least one other company is pursuing silicon-oxide based non-volatile memory. Intrinsic Semiconductor Technologies Ltd. (London, England) has made examples of its silicon oxide-based ReRAM on a 50nm CMOS manufacturing process. The work was done in partnership with research institute IMEC (Leuven, Belgium). Intrinsic is a 2017 spin-off from University College London.
Related links and articles:
Weebit takes silicon-oxide ReRAM to 22nm FDSOI
Weebit Nano puts silicon-oxide ReRAM on 28nm FDSOI
SkyWater foundry to take Weebit ReRAM to volume
Chinese ReRAM startup raises $100 million
Leti, CMP offer OxRAM multiproject wafer service
Fujitsu takes Nuvoton ReRAM to 12Mbit
SiOx memory startup scales ReRAM devices to 50nm