Intrinsic’s Resistive Random Access Memory (RRAM) is a truly embeddable non-volatile memory – elegantly CMOS friendly.

Invented by Professor Tony Kenyon and Dr Adnan Mehonic at University College London, Intrinsic’s silicon oxide (SiOx) memristor is changing what is possible with standard digital logic semiconductor devices. Integrating non-volatile memory will become quick and easy, and will offer huge speed and power benefits over current architectures.

Intrinsic’s silicon oxide-based RRAM will transform the semiconductor industry’s use of embedded memory

The Non-Volatile Memory Problem

All digital chips have memory embedded within them. This memory contains the program code which they execute and holds data capturing the state of the system. For the vast majority of chips, this memory is volatile – i.e., when the power goes off, the memory is lost. This is a major inconvenience, especially for anything which is battery powered or otherwise not connected to the power grid. The most common way to solve this problem is to have an addition external memory chip (such as a Flash chip) and re-load the data from this second chip at start-up or when it is needed. This takes more power, more time, more board space and is expensive. Another way to address the problem is to embed Flash memory in the digital logic chip. However, due to incompatibilities between Flash and digital logic manufacturing processes, this condemns the chip to be made on a slower and more power-hungry older technology, so this technique is less often used. Today, the industry has to live with these limitations.

The Industry Challenge

Many researchers are looking for a physical phenomenon in semiconductor materials which exhibits ‘non-volatile memory’, i.e., material that can be put into two or more distinct states and that remains in those states until commanded to change state. The phenomenon needs to be at the nano scale, it needs to be fast to read (and the act of reading it should not perturb it). The states need to be stable at high temperatures (e.g. 270 degC to survive soldering), they need to last for years and be re-usable over millions of cycles. Yet we would like to be able to change states with very little energy. To make matters even more challenging, this ideal device needs be constructed using materials and processing steps that are commonplace in the manufacturing of digital semiconductors. This is a pretty tall order which Flash memory, and most emerging non-volatile memories, fail on several counts.

The Solution

The nanoelectronics team at University College London have been working on this challenge for many years and have invented a very exciting memristor device based on silicon oxide which appears to satisfy all aspects of this challenging brief. Intrinsic has been set up by the researchers and industry experts to turn this exciting device into a product available to anyone building a digital logic chip.

Intrinsic’s Memristor Device Explained

Memristors

A memristor is a resistor with memory. I.e., a resistor whose value can be changed (set and reset) with the application of a specific voltages. The value of the resistor can then be read using a smaller voltage which does not affect the value of the resistor. This allows the memristor to be the basis of an electronic component with memory, either digital or analogue.

The Intrinsic Memristor

Intrinsic’s device is based on a silicon oxide switching material. A conductive path between the two electrodes is formed by creating a filament of ‘oxygen vacancies’. By varying the amount of oxygen in the filament, the conductivity of the filament can be reversibly changed between a low and a high resistance state, or many states in-between.

Given the filaments are sites of oxygen vacancy rather than atoms of an introduced metal as in some memristors, the filament does not defuse into the bulk of the silicon oxide. It stays in its defined state until oxygen is forced in or removed by the set/reset process. This has two fundamental benefits. Firstly the filament is very stable. It has been shown to be stable at 270 degC and higher, more than adequate for solder reflow temperatures. Secondly, there is no additional material to bring into the semiconductor processing and therefore no possibility of contamination, which is a real issue when working with new materials.