The control of magnetic properties using electrical currents is a central activity in the fast-moving research field of nanospintronics. The underlying mechanism, called spin-transfer torque, offers fundamentally new insights into the interactions of charge and spin as well as prospects for new high-density storage devices, non-volatile memories and microwave emitters and filters. A key challenge here is to minimise the magnitude of the critical currents required while maintaining thermal stability. It has recently been demonstrated that, in ferromagnetic semiconducting materials based on III-V compounds, the critical currents required can be orders of magnitude lower than in metals. These materials also offer the ability to precisely tune and control their properties, so that ferromagnetic semiconductors form an ideal testing ground for enhancing the understanding of spin transfer torque and related effects.This proposal is for an extensive 3 year collaborative programme of research which aims to investigate aspects of both the fundamentals of charge and spin interactions and transport in spintronic devices and the potential of nanospintronic devices to provide a new paradigm for future electronics. We focus on the interaction between an electrical current and local spins in nanowires and tunnelling structures. Through this project we will develop novel device structures in order to address open questions of technological importance, including the role played by spin-orbit coupling and the compatibility with semiconductor technology. A particularly novel aspect of this project is that it exploits the extreme flexibility of ferromagnetic semiconductor systems to understand the fundaments of these effects while also exploring them in room temperature ferromagnetic metal systems. The project brings together complementary expertise of leading semiconductor spintronics research groups in the UK and China, firmly establishing a new collaboration while also strengthening existing ones, and exploits recent achievements by each participant in state-of-the-art materials development and new device concepts.
The aim of this project is to design and demonstrate novel non-volatile and extremely low-power logic systems by hybridizing the newly developed three-terminal metal oxide device, Atom Transistor and nano-electro-mechanical (NEM) systems for future beyond von Neumann computing. The hybrid systems are investigated theoretically and experimentally using world-leading nanotechnologies of the NIMS team in Japan and the Southampton team in the UK. The operation of the systems is studied both on the device and circuit levels by using a multi-scale hybrid modelling. Basic circuits such as inverters and power management systems are designed utilizing the unique characteristics of the Atom Transistors and NEM switches. The duality of volatile and non-volatile operations of the Atom Transistors enables to design a new type of non-volatile logic systems which is similar to neurons in the brain. A novel bistable sleep transistor is also designed based on the recently developed suspended-gate silicon nanodot memory (SGSNM) technology for advanced power management architectures. Prototyping the systems is carried out jointly by transferring samples as well as technologies between the two teams, and electrical testing the circuits is conducted using state-of-the-art characterization tools at Southampton Nanofabrication Centre. The first demonstration of the revolutionary non-volatile logic systems towards information technology in the next generation will provide opportunities to companies for further development and commercialisation in both Japan and the UK. This will thereafter contribute to further enhance the existing economic relations between the two countries as well as strengthening their economies.
"Quantum systems" describes physical systems in which the elementary excitations are quantised as small packets of energy. Examples include individual photons of light, vibrations of crystals (phonons), and excitations of magnetic systems (magnons). The ability to control these elementary excitations can lead to the development of revolutionary new technologies such as quantum computers, secure communication through quantum encryption, and sensing technologies for navigation, geophysical exploration and medical imaging. Crucial to these technologies is the ability to transfer the quanta of energy between different physical systems in a coherent way that preserves the information encoded within the quantum states. This is achieved by "overlapping" or hybridising the quantum states of the systems. Many research groups are working on ways to achieve quantum hybridisation in different physical systems. Recently, a field of research known as "Cavity Spintronics" has achieved quantum hybridisation between microwave photons, magnons and phonons. However, these experiments require bulky, centimetre-size microwave cavities and large, millimetre-size magnetic spheres, which are not suitable for the development of technological applications. The project we propose will develop a fully on-chip architecture for coupling microwave photons with magnons and phonons in a micron-size ferromagnetic element. The on-chip architecture will lend itself more easily to integration with other physical systems such as optical cavities, acoustic resonators and superconducting qubits (the building blocks of quantum computers). Our proposal will build upon two recent developments. Firstly, we have developed a novel method to create a large overlap between magnon and phonon states in thin magnetic layers and have demonstrated the first hybrid magnon-phonon state in a micron-scale extended magnetic structure. This was achieved by patterning the layer's surface with a shallow periodic stripe pattern, which created confinement of the phonon and magnon modes and caused them to overlap. Secondly, research groups, including our project partners at the Hitachi Cambridge laboratory, have recently developed methods to overlap microwave photons with micron-scale magnetic structures in on-chip architectures. This proposal will build upon these two key developments by fabricating microwave circuits on electronic chips containing micron-size patterned magnetic structures, in which hybrid magnon-phonon states are formed. The overlap with the photons in the on-chip microwave circuit will lead to hybridisation between all three systems (photons, magnons and phonons). Furthermore, microwave circuits can be readily controlled and detected using standard laboratory measurement instruments. This will allow us to excite and probe the magnons and phonons using the microwaves. Our proposal to make fully on-chip hybrid photon-magnon-phonon systems will yield significant technological advantages that could lead to new applications in the realms of quantum computing, communications and sensor technology. It will enable investigations of the fundamental properties of photons, magnons and phonons and of the interactions between the different quantum systems.
Si photonics is achieving a drastic innovation for optical networks in terms of low power, low cost, high bandwidth, and large-scale integration capabilities with smart electronics fabricated in ubiquitous infrastructures of Complementary-Metal-Oxide-Semiconductor (CMOS) foundries. Optical networks have been already introduced by using III-V compound semiconductors for long-hall communications, which require higher performance over the cost. Si photonics should not compete in this field, since the industries will not grow just by replacing these markets with Si photonics. Si Photonics is more promising in short-reach optical interconnections, which requires lower power consumption and lower fabrication costs. CMOS technologies are ideal in mass production to provide significant numbers of optical components required for short-reach communications such as backplane board-to-board, intra-board chip-to-chip, and intra-chip optical interconnections. Si optical modulators, which convert the electrical signals to the optical signals on a chip, are the most important building blocks for Si photonics. Here, we will develop the world's best low power Si modulators, which can be driven by the CMOS front-end driver circuitry. We will introduce the atomically flat Si fin technologies for the first time in optical modulators to develop the MOS-type Mach-Zehnder Interferometer (MZI) with a slot waveguide and the SiGe fin based Electro-Absorption (EA) modulators for short-reach interconnections and chip-to-chip applications, respectively. We anticipate that these devices will be widely used in data centres for cloud computing and network routing, contributing to reduce the power consumptions substantially, while increasing bandwidths. Our first target of Si fin MZI optical modulators is aiming for the near term application to C form-factor pluggable 100-Gigabit-ethernet (CFP100GE) in multi-source agreement (MSA) at the 1310-nm wavelength region. We think that this is a natural choice of technology, since we have no MSA at the wavelength of 1550-nm, and a MZI has a better technological-readiness-level over an EA modulator. For the longer term, however, a EA modulator can exceed its performance over MZI. Therefore, the other target for our SiGe fin EA modulator is the energy demanding chip-to-chip interconnection application by using the 1550-nm wavelength range, where no standardization exists at this moment. We will realize truly low power performance including a CMOS driver and laser diodes. Therefore, our project will cover both 1310-nm and 1550-nm wavelength ranges for near-term businesses and leading future technology trends.
Many of the components in modern technological devices such as computers, communications devices (e.g. mobile phones) and sensors are made on a very small scale from magnetic materials. For example, modern computer hard drives and magnetic random access memory (MRAM) contain magnetic elements that are a few tens of nanometres in size. In such devices the direction of the magnetisation of the magnetic elements is used to store information. Controlling the direction of magnetisation is achieved by using electrical current to generate a magnetic field locally or by passing an electrical current through the device using an effect called spin transfer torque . These techniques have disadvantages arising from the energy dissipated in applying electrical currents, the limits on miniaturisation (due to the need to integrate the components which generate the field with other magnetic devices) and the difficulty in addressing individual elements due to stray magnetic fields. A solution to these problems would be to create devices in which the magnetic state is controlled by applying electrical voltages. In this project I will do this by adopting a novel approach, combining the magnetic material with piezoelectric material in hybrid devices. Piezoelectric material has the property that it will physically expand or contract when an electrical voltage is applied to it. This can be used to transfer strain to the magnetic material. Certain magnetic materials have large magnetostrictive properties, which means that if they are strained then the magnetisation direction will rotate. For example, I will study the magnetostrictive transition metal alloys FeCo, FePd and FePt. I will study the magnetic properties of these materials in the bulk and on the nanoscale using modern characterisation techniques such as Superconducting Quantum Interference Device (SQUID) magnetometry and Magnetic Force Microscopy (MFM), and I will use state of the art growth and fabrication techniques (e.g. sputter deposition and electron beam lithography) to fabricate devices a few tens of nanometres in size. By conducting electrical transport experiments at GHz frequencies (comparable to the frequencies used in modern computing technology) I aim to demonstrate ultra-fast switching of the magnetic state of the devices by applying ultra-fast (picosecond) voltage pulses. The nanoscale devices will also be used to study the fundamental physics of phenomena such spin transfer torque . Another class of devices that I will study are nano-electro-mechanical systems (NEMS) which consist of nanoscale oscillating beams and cantilevers. Such devices have potential applications as highly sensitive weighing scales and are also interesting for more fundamental studies of the overlap between quantum and classical physics. The use of magnetostrictive ferromagnetic materials to fabricate NEMS will offer new means to detect and drive the mechanical oscillations.This proposal presents exciting opportunities to study fundamental physical phenomena in new material systems and promises to produce knowledge of new phenomena and new functionalities in nanoscale devices. The results of this work will contribute to the design of future computing, communications and sensor technologies.