ECCS - EPSRC Development of uniform, low power, high density resistive memory by vertical interface and defect design

The future of energy-efficient computing will increasingly move from being compute-centric to being memory-centric. There is a huge-energy cost of storing and moving data, which is much higher than computing it. Indeed, memory dominates compute energy (>4X) in data-intensive applications. New ultralow power non-volatile memory (NVM) is central to all aspects of computing, from stand-alone, storage class memory (SCM) for use in data centres, to embedded non-volatile memory (e-NVM) for IoT, the automotive industry, etc, to new forms of computing. The area is growing hugely, along with the associated energy consumption, e.g. data centers will use >10% of global electricity by 2030 with a market growing ~10% per year, to >$150 billion by 2023. Such efficiency cannot come from processing as Moore's law reaches an end and new processor technologies are not yet established. The biggest performance and energy saving gains will be in memory. The replacement of standard memory with high performance memory NVM could reduce power usage by more than 60%.

Of the many candidate NVM forms under intense investigation, oxide resistive RAM (RRAM) has the greatest potential in terms of cost, density, simplicity and potential for 3D integration. However, several challenges currently exist, notably the need for a forming voltage, poor uniformity, scaling, and endurance. The aim of this project is to overcome these challenges. It will be done by adopting our ground-breaking results from an ideal system to an industry platform. So far, in the ideal system, we have demonstrated that a) precise and non-random conducting channels can be engineered into films to eliminate the need for a high voltage forming process; b) high and controlled oxygen vacancy concentrations lead to highly and reproducible on-off ratios; c) eliminating use of transition metals produces low leakage and strongly reduces variabilities from film to film. The industry platform we will explore in this project is doped HfO2, grown by sputtering and atomic layer deposition.

An internationally leading team with more than 15 years of very strong collaboration in the area of the proposal will undertake the work. First, growth of VAN films using pulsed laser deposition (PLD) will be undertaken at Purdue University. PLD is the simplest way to make the most perfect metal oxide films in a rapid way. These will enable us to understand the RS processes more fully and will provide information on how to grow the films by the industrially scaleable processes. Both Purdue and Cambridge will be involved in the HfO2 nanostructure film design for PLD. The knowledge from the PLD growth will then be translated to the sputtering and ALD approaches undertaken at the University of Cambridge. The effort at the University at Buffalo will focus on the fabrication and testing of prototype memristors and RRAMs using the RS films deposited by Purdue University and University of Cambridge. State-of-the art (some in-operando) characterisation tools will also be central to materials understanding and device optimisation and these will be used at Purdue and Cambridge. A very strong interaction between the groups, with regular sample and knowledge transfer will take place. Our ultimate goal is a forming free device, with on/off ratio~104, endurance >1012, <10pJ per switch, uniformity of few %, scaled to 20 nm.

In terms of training, we will educate graduates in materials sciences and electronic engineering. We will train more than 3 early career researchers in world-leading research environments in the US and UK, with several companies involved (small to large), including the Cambridge company ARM who are very active, both in the UK and US, in the memory area.

New high performance NVM is critical to many technology sectors, i.e. in transport, medicine, communications, and IoT. The total market for all these areas is huge, i.e. $ Trillions. Industry adoption of high performance advanced NVM memory would have a huge impact on all these technologies. If our proposed solutions for oxide RRAM are successfully translated to an industry platform then we will have achieved a game-changing NVM technology and it will have a huge impact on future technologies. This will lead both to the creation of many new high tech jobs and to an improvement in quality of life by reducing CO2 emissions. Hence, there is the potential for strong societal impact.

In terms of academic impact, the strong global competition for skilled personnel and the increasing international competition in new technologies, particularly in advanced materials, means that training of a number of high quality engineers and scientists is crucial. The broader training we will provide the team in advanced memory technology will feed not just into the academic community but also into high tech industries. Such industries all report difficulties in finding skilled people, including the companies we will collaborate with in this project.

Strong industrial manufacturing bases in high technology areas to enhance the knowledge economy are very important in both the UK and US for high value-added job creation, and these are current priorities of both governments. Indeed, the advanced NVM topic lies at the heart of a number of UKRI priority areas related to both economic impact and improved quality of life: Advanced materials for NVM aligns with the Government's 2017 industrial strategy white paper. The first grand challenge is, 'put the UK at the forefront of the artificial intelligence and data revolution', mentioning ARM's microchips as being a great underpinning technology. NVM technologies are also key to advances in cognitive computing, boosting the development of artificial intelligence. A second UK grand challenge is 'Clean Growth', with 'development, manufacture and use of low carbon technologies'. The need for NVM in electric vehicles and a very wide range of other green technologies, ideally places NVM development under this second challenge area. NVM development aligns also with UKRI priorities under the following themes: 'manufacturing the future', 'the digital economy', and 'ICT'. NVM also fits under the Eight Great Technologies areas of 'Advanced Materials' and 'Big data and energy efficient computing'.

The development of advanced memristors and NVM is also of great interest to the US private sectors and US government, in all the same areas as listed above for UK government priorities. Currently, exascale computing systems have been planned for 2020 through 2022 in US. Other priorities in the US are improving security circuits for the IoT and AI chips, and computer-in-memory for deep neural networks. NVM is a key technology for these areas.