Writing for Semiconductor Engineering, Ernest Worthman notes that next-generation IoT/E devices will face a plethora of power, footprint and electronic constraints.
According to Steven Woo, VP of solutions marketing and distinguished inventor at Rambus, non-volatile memory (NVM) could very well play an important role in the IoE of the future.
“NVM doesn’t consume any power during non-use, which is a requirement for many of the low-power IoE devices that are going to need to draw very little power during turn on and turn off and no power at rest,” Woo told the publication.
“In the future, when one is talking about IoE devices, by far the No. 1 design goal is to have as small as possible power budgets. There are [also] some things about this platform [ReRAM] that makes it a bit easier to integrate in terms of the existing SoC design flow.”
While it still may be a bit early on the memory development map for geometries lower than 20nm (a top-shelf target density), a number of ReRAM advantages are already quite clear.
“It has a simple structure with good scalability [and] offers high speed, with switching times as low as 10ns, at low power. It has the ability to switch a bit using only 1 femtojoule,” Worthman explained.
“And it has a very desirable feature—ease of integration with CMOS back-end-of-the-line processes. Finally, it has the potential to be built in extremely dense crossbar arrays.”
Woo concurs, although he acknowledges that there are still a number of technical issues to work out with ReRam, including integrating the memory with existing manufacturing processes.
So, how does ReRAM work? Simply put, ReRAM uses resistance rather than electrical charges to alter the bits within a cell.
“The [basic] principle is that when voltage is applied, the resistance changes. The state change is, of course, from zero to one, or vice versa,” Worthman explained. “Being a type of NVM, once the state is set, it remains set until the next change cycle.”
Of course, not all ReRAM is alike.
“Depending on what the application may be, the different types can have different underlying material, which support distinct properties, such as various access times, retention capability and power consumption,” he continued. “For example, certain fabrications provide best-of-breed data retention while others can exhibit extremely fast read/write times.”
In addition, says Worthman, ReRAM makes use of a “memristor,” or memory resistor.
“This is a form of passive circuit element, which maintains a relationship between the time integrals of current and voltage across a two-terminal element. Essentially, it is a nanoscale voltage-controlled resistor,” he explained.
“One type of ReRAM consists of titanium oxide as an insulator. One side of it contains oxygen molecules, which move across to the other side if a voltage potential is placed across it, reflecting a ‘1’ state. Returning the oxygen molecules to the other side returns the memory to the off state.”
According to Worthman, typical applications for ReRAM include computer memory, microcontrollers, smartphones, tablets, automobile navigation systems and digital cameras.
“Once high-density arrays can be reliably produced, ReRAM will have a lot of applicability for IoE devices that need fast switching and low power,” he added. “[Plus], its flexible configurability, via materials, means it can be used in a wide variety of IoE devices.”
It should be noted that Rambus recently confirmed a RRAM partnership with researchers at Tsinghua University in Beijing, China. According to Rambus Labs VP Gary Bronner, RRAM could potentially capture a lucrative position between flash memory and DRAM.
“Many semiconductor companies have expressed a strong interest in ReRAM,” Bronner concluded. “As such, our collaborative goal with Tsinghua researchers is to explore how to further improve the non-volatile memory so that it is ultimately suitable for consumer devices as well as more demanding platforms and environments.”