An innovative non-volatile memory technology that could scale further and perform better than flash memory and resistive RAM (ReRAM) technologies has attracted the interest of processor licensor ARM Holdings plc (Cambridge, England), according to Carlos Paz de Araujo, a professor at the University of Colorado who is the leading advocate for development of the memory.
Professor Araujo told Electronics 360 that his company Symetrix Corp. (Colorado Springs, Colo.) has secured ARM's support for research into a non-filamentary, non-volatile memory technology based on the metal-insulator Mott transition in nickel oxide and other transition metal oxides (TMOs). In email correspondence he said that Symetrix, ARM, the University of Colorado at Colorado Springs and the University of Texas at Dallas, are engaged in research on what he has dubbed Correlated-Electron RAM (CeRAM).
The exact goals, duration and budget for the research were not revealed although Professor Araujo said Symetrix would soon have data on CeRAM devices as small as 5 nanometers made using an atomic force microscope. He said this data would demonstrate the "new switch" capabilities of the device. To date CeRAM devices have only been fabricated at dimensions of about 0.8 micron.
It also remains unclear how soon CeRAM devices could be made commercially. Typically R&D that is beyond the scaling of mainstream silicon manufacturing processes and materials has taken many years.
However, Professor Araujo has been working on the technology for about five years and there is a large body of resistive RAM (ReRAM) research in place globally as non-volatile memory has been a hotly pursued research topic for several years. This has been due to the expectation that flash memory would cease to scale beyond about the 20nm node. But while various ReRAM approaches have been tried – often based on layered metal-oxide structures – most of these have been based on the making and breaking of conductive filaments within an insulating layer between top and bottom electrodes. Usually electroforming voltages and cycles are also required. Understanding the physical processes that govern the formation, maintenance and breaking of such filaments has proved difficult.
The claim is that the CeRAM differs from other ReRAM developments in that it does not depend on atomic transport to make and break filaments, which brings with it issues of thermal dependence and reliability. Instead the CeRAM is based on a metal-insulator transition that occurs throughout the crystal structure based on quantum mechanical electron correlation effects, according to academic papers published by Professor Araujo in recent years. This can be considered as a quantum mechanical tuning of electron bands in the material due to electron-electron effects within atoms.
According to the Symetrix website TMOs are subject to a metal-insulator transition that is induced by field or voltage. In the case of nickel-oxide it is a 0.6 volt to write an insulating state and 1.2 volts to write a conductive state. The state is robust up to 400 degrees C and can be read with a voltage of 0.1 to 0.2 volts. Devices albeit at large geometry have reported 10^12 read cycling endurance. "There is no rupturing and reformation of filaments. There is no oxygen diffusion (memristor), only a pure Mott (charge transfer) phase transition," Symetrix states on its website.
Although ARM is best known as a licensor of processor-related intellectual property it is investigating non-volatile memory as it is becoming increasingly relevant to achieving energy-efficiency goals for future mobile and Internet of Things (IoT) applications.
Professor Araujo founded Symetrix in 1986 to commercialize ferroelectric materials for use in non-volatile memory. Symetrix promoted the use of strontium barium titanate as an alternative perovskite to lead zirconate titanate (PZT) for use in non-volatile ferroelectric random access memories (FeRAMs). Symetrix, which operates an IP-licensing business model, has licensed its technology to a number of semiconductor companies.
Symetrix claims to have received worldwide patent coverage on CeRAM technology including 3D memories, a low temperature process that is CMOS-friendly for embedded applications in the microcontroller and SoC areas.
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