ReRAM

ReRAM (Resistive RAM, ReRAM, RRAM)

ReRAM (Resistive Random Access Memory) is a type of non-volatile RAM. The data is therefore retained for a long time, even if the power supply is interrupted. In this entry, we will provide a simplified description of how ReRAM works.

Let's start by looking at the individual components of the term, as they give us an insight into the characteristics of this storage technology.

Resistive:
The term "resistive" refers to the electrical resistance: ReRAM is characterized by the fact that it uses the resistance behavior of special materials to store data.

Random Access Memory:
Like any other RAM type, ReRAM is also characterized by "random access" or direct access to memory cells. This means that each memory address can be accessed directly and at approximately the same time, independently of the others. This distinguishes RAM from sequential storage media, where the access time depends on the position of the data.

Properties of ReRAM

Non-volatile
As already mentioned in the introduction, ReRAM is a non-volatile memory technology. This means that data is stored even when the power supply is switched off. This distinguishes it from many other types of memory that need to be constantly supplied with power in order to retain their data (such as DRAM).

High storage density
ReRAM can store a large number of bits in a small physical space. This means that several states can be stored in a single cell, resulting in a high memory density.
This means that ReRAM has the potential to achieve a higher storage density than, for example, flash memory, DRAM or SRAM, as these can typically store one or two bits per cell (through different charge states). More importantly, ReRAM offers the ability to stack memory cells in multiple layers (a process known as "3D stacking").

3D stacking
As the name suggests, 3D stacking technology allows several layers of ICs to be stacked on top of each other, thereby increasing the density of the components and the speed of communication between the components.

ReRAM is suitable for 3D stacking due to its special structure and mode of operation. At its core, a ReRAM cell is a two-terminal device (a so-called "memristor") in which the resistance state can be changed by applying voltage. This mechanism is relatively simple and compact, making it well suited for multilayer applications. In addition, ReRAM cells generate less heat compared to other memory technologies, which is a critical factor in 3D stacking.

Application-specific suitability of ReRAM

A brief note in advance: Whether the use of ReRAM is recommended for certain applications cannot be said in general terms and always depends on a variety of application-specific factors. With the following information on the suitability of ReRAM for various application areas, we therefore do not wish to make any purchase recommendations, but rather to put the properties of ReRAM memory technology into context.

Artificial intelligence (AI) and machine learning (ML)
AI and ML algorithms process large amounts of data and require high memory density and speed. ReRAM can provide the necessary capacity and speed to run these algorithms efficiently. A concrete example could be an autonomous vehicle that uses AI to analyze its environment and make decisions. The high memory density and speed of ReRAM could improve processing performance and increase energy efficiency.

Internet of Things (IoT)
To maximize battery life, IoT devices need memory that consumes little energy. It must also be able to store data even when the device is switched off. ReRAM's non-volatility and low energy consumption make it ideal for these applications. A concrete example is a networked thermostat that stores temperature data over an extended period of time in order to efficiently control the home's heating and cooling system.

How the ReRAM works

The way ReRAM works is particularly interesting. As with other memory technologies such as MRAM (Magnetoresistive Random Access Memory) and PCRAM, ReRAM represents the states 'logical-0' and 'logical-1' by different, measurable resistors. The unique thing about ReRAM, however, is how these resistors are generated.

ReRAM memory cells use the resistance behavior of special materials to store data. In contrast to other forms of memory, such as DRAM or flash, in which information is stored using charge carriers (electrons), ReRAM stores information using the resistance of the memory cells.

The basic idea is as follows: Conductive channels can be created on a substance that conducts electrical current poorly or not at all (this substance is called a dielectric) by applying a sufficiently high voltage. Current can then flow through these conductive channels - the dielectric is thus 'reprogrammed' to generate different resistances, which then represent the states 'logical-0' and 'logical-1'. What is particularly useful for our purposes is that this state is maintained even if the power supply is interrupted.

Sources

• Emerging Non-Volatile Memories; Seungbum Hong, Orlando Auciello, Dirk Wouters (https://link.springer.com/book/10.1007/978-1-4899-7537-9)
• Elektronik-Kompendium (RRAM / ReRAM - https://www.elektronik-kompendium.de/sites/com/1909161.htm )
• Resistive Switching: From Fundamentals of Nanoionic Redox Processes to Memristive Device Applications; Daniele Ielmini, Rainer Waser - (https://www.wiley.com/en-us/Resistive+Switching%3A+From+Fundamentals+of+Nanoionic+Redox+Processes+to+Memristive+Device+Applications-p-9783527680931)
• Wikipedia DE (Resistive Random Access Memory - https://de.wikipedia.org/wiki/Resistive_Random_Access_Memory )
• Wikipedia EN (Resistive Random Access Memory - https://en.wikipedia.org/wiki/Resistive_random-access_memory )