https://www.techtarget.com/searchstorage/definition/RRAM-or-ReRAM-resistive-RAM
RRAM, also known as resistive random access memory or ReRAM, is a form of non-volatile storage that operates by changing the resistance of a specially formulated solid dielectric material. An RRAM device contains a component called a memristor -- a contraction of memory resistor -- where the resistance varies from a high-resistance state to a low-resistance state when different voltages are imposed across it.
Normally, a dielectric material doesn't conduct electric current. In fact, dielectric substances are used in capacitors for the specific purpose of preventing the flow of current and maintaining separation of electric charge poles. If a sample of dielectric material is subjected to a high enough voltage, it suddenly conducts because of a phenomenon called dielectric breakdown.
In conventional dielectric material, breakdown causes permanent damage and failure of the associated component. In a memristor, the dielectric breakdown is temporary and reversible because of the materials used.
Resistive RAM has a resistive switching memory cell with a metal-insulator-metal structure. These RRAM cells use a method of creating physical defects in a layer of metal oxide material. These defects are called oxygen vacancies. The vacancies represent two values in a binary system. RRAM works like a semiconductor, which uses electrons and holes to create the binary system rather than oxygen ions.
In one form of memristor, a deliberately applied operating voltage causes the medium to acquire microscopic conductive paths called filaments. Filaments result from various phenomena, such as metal migration or physical defects. Once a filament appears, a different external voltage can be used to break or reverse it.
The controlled formation and destruction of filaments in large numbers enable the digital data retention and data storage. Numerous substances have been tested for memristor characteristics, including nickel oxide, titanium dioxide, various electrolytes, semiconductor materials and even some organic compounds.
Another memristive form uses voltage to cause a change in the state of an amorphous solid called chalcogenide glass. This technique flips chalcogenide glass rapidly from a hardened state to a more fluidlike state, changing the resistance of the material.
RRAM memory and storage devices are available; however, their use hasn't gathered momentum. Typical use cases involve requirements for non-volatile memory (NVM) and storage, including high speed, low latency, low power use and durability. Among frequently cited applications are artificial intelligence (AI), machine learning and the internet of things (IoT).
Storage class memory (SCM) is envisioned as a bridge between existing storage technologies and main memory. It uses non-volatile NAND solid-state memory with its speed, hard disk drive technology and storage capacities to provide options for existing flash memory and storage devices. The use of RRAM technology in lieu of NAND could become an important application.
Higher switching speed is the principal advantage of RRAM over other non-volatile storage technologies, such as NAND flash. Timescales as short as 10 nanoseconds have been observed. Memristor filaments can occur in dimensions as small as a few nanometers, a tiny fraction of the wavelength of visible light in free space, offering the promise of high storage density. The occasional formation of unintended filaments, called sneak paths, presents a challenge for engineers intent on the large-scale development of memristor technology and RRAM devices.
RRAM and other memristor technologies also draw much less power than NAND flash. That makes them well suited for memory in sensor devices for industrial, automotive and IoT applications. As the cost of manufacturing RRAM and other memristors drops, they're expected to become competitive with NAND flash.
High-density memory, fast read/write speeds and low power consumption are reasons why memristor-based memory technologies are among the most anticipated replacements in applications like solid-state drives (SSDs) and non-volatile dual in-line memory modules, or NVDIMMs. Several companies make RRAM chipsets and memory units. However, costs must decline for the technology to compete with existing NVM and storage systems.
In addition to RRAM, other memristor technologies in various stages of development or market presence include conductive-bridging RAM (CBRAM) and phase-change memory (PCM).
CBRAM uses a layer of electrolytic material through which the conductive filaments are created and destroyed. The resistance in the dielectric material decreases or increases based on whether the filament exists or not. This technology is available from Adesto Technologies as ultra-low-power memory components and electronic devices for IoT applications.
In contrast, PCM applies a current to the dielectric material to change the state of chalcogenide glass from more solid to less solid. Initially, the development was focused on finding the best material for achieving these two states. More recent work is focused on allowing the material to hold multiple states of variable levels of crystalline or amorphous states.
Sharp Corporation owns the registered trademark "RRAM" in several countries. According to TechTarget research and RRAM-info, vendors manufacturing RRAM-based chipsets and memory devices include the following:
RRAM technology is being built into a variety of devices. However, the popularity of NAND and other NVM technologies means that RRAM is still working to establish itself. Factors impacting the future of RRAM technology include the following:
The many organizations committed to RRAM must overcome technology hurdles, boost cost-effectiveness, establish viable use cases and characterization, and convince the semiconductor industry of its value. Progress in those areas will enable RRAM to play an important role in next-generation storage and memory applications and systems.
Flash memory plays a key role in enterprise storage. Learn about flash architecture, types and products in our comprehensive flash memory guide.
10 Jul 2024