Theory, Modelling & Design

 

Research in the Theory Modelling and Design Centre (Theory) at Tyndall is very well matched to Tyndall’s major research themes and application areas. The Centre hosts 50 researchers whose interests span Photonics, Micro/Nanoelectronics and Microsystems. Research in the centre addresses a mixture of problems. These include fundamental investigations and development of theoretical techniques, as well as the application of existing techniques to address problems of more immediate and applied relevance.

Miniaturization, the great driving force for the information technology and electronics industries, is now approaching its theoretical limits. As electronic device dimensions shrink to the molecular scale, theory and modeling assume an ever greater role.  Theory enables rapid investigation and analysis of new ideas and discoveries, prior to committing to an expensive practical implementation or development phase. Engineers and scientists in Tyndall’s Theory, Modelling and Design Centre specifically investigate new materials and their properties for uses in future electronic and photonic devices. Using a unique set of tools and skills developed through years of expertise the researchers can rapidly identify the most promising research directions, and quickly focus efforts in those areas saving significant time and money.

Among recent highlights, Theory Centre researchers have:

  • shown that the junctionless transistor concept should work beyond the limits of current silicon technologies;
  • developed in electronic systems research ultra-efficient miniature radar  sources for use in compact sensor systems;
  • identified in optical materials research that the use of “quantum dot” nanostructures can extend efficient LED emission to amber and UV;
  • used molecular dynamics simulations, in collaboration with experimental researchers in the Netherlands to show ‘two legged' molecules walk, hop and fly across a receptor surface, relevant to understanding how viruses and bacteria interact with cell membranes.

Much of the research in the Centre is undertaken in close collaboration with industry partners. Intellectual property related to design of p-doped transparent conducting oxides has recently been licensed to Umicore, while a method for designing semiconductor lasers has been licensed to Eblana Photonics in Dublin. The Thin Film Simulation Group, supported by Enterprise Ireland, is working with Henkel in Dublin on scalable deposition processes for semiconductor packaging and with Analog Devices in Limerick to develop high-k integrated capacitors. Tyndall theory researchers are leading a European project to develop standalone dust-sized chemical sensing platforms that harvest energy from ambient light, and leading a further European project to significantly reduce power consumption at the component and system level in advanced communication systems.

Key Recent Highlights

Ultra-Short Optical Pulses “Squeezing” the Vibrations of a Bismuth Crystal

In collaboration with x-ray scientists at the Paul Scherer Institute’s Swiss Light Source, Stephen Fahy and former Tyndall student, Eamonn Murray, have demonstrated how atomic forces can suddenly be altered by an intense pulse of light. In an effect called “phonon squeezing”, the vibrations of the material are suddenly thrown out of equilibrium. This “squeezing” was identified by oscillations in the intensity of ultrashort x-ray pulses scattered from bismuth – the first time such oscillations were observed directly in any material. Understanding and controlling how light alters the forces between atoms is central to our understanding of photo-chemistry and underpins many areas of energy science, such photosynthesis. Tyndall and its collaborators are one of only a few groups worldwide with the ability to measure and calculate such atomic motion.

Oscillations of the intensity of x-ray pulses scattered from bismuth, following excitation. This work was highlighted in the review journal, Physics

(http://physics.aps.org/viewpointfor/
10.1103/PhysRevLett.102.175503
)

 

Are we only a hop, skip and jump away from controlled molecular motion?

Widespread industrial uptake of nanotechnology requires cheap, easy and robust solutions that allow manipulation of matter at the smallest scales and so a key enabling feature will be the ability to move material around, molecule by molecule. Molecular dynamics simulations by Damien Thompson, in collaboration with experimental researchers in the Netherlands have shown for the first time the range of ways in which ‘two-legged' molecules walk, hop and fly across a receptor surface. Controlling how molecules move on such surfaces could be the key to more potent drugs that block the attachment of viruses to cells, and will also speed development of new materials for electronics and energy applications.

Molecular motion on a receptor surface
[From Nature Chemistry 3 317(2011)]

Atomic scale simulation of Junctionless Transistors

Tyndall researchers Giorgos Fagas and Jim Greer have developed techniques to calculate how electric currents flow within semiconductor nanowires. Nanowires have small diameters of only a few atom widths, but can be fabricated with lengths thousands of times longer than their diameters. Their recent work has shown that the junctionless transistor concept of Jean-Pierre Colinge’s Ultimate Silicon Devices Group, should work beyond the limits of current silicon technologies. Their work also highlights some interesting twists and quantum surprises for device physics at this length scale. The software package which they have developed for transport simulation has recently been licensed for evaluation by Intel. 


Doped silicon nanowire for transistor simulation

New materials for see-through electronics

Michael Nolan and Simon Elliott, collaborating with partners in an EU-funded project called NATCO, have developed a new material that is simultaneously semiconducting and transparent.  In terms of its transparency across a wide range of wavelengths, the new Tyndall material is better than existing materials in its specific class of so-called p-type transparent conductive oxides (TCOs). The material was designed at Tyndall entirely through computer simulation, by simulating how different elements from the periodic table affect the transparency and conductivity of a known material, copper oxide.  This approach yielded a set of design rules that were applied to other existing TCO materials in order to determine the optimum composition. The resulting new TCO material, barium-doped strontium copper oxide was synthesized by Umicore, a leading materials company with headquarters in Belgium. An increase of transparency beyond visible light into the infra-red and ultra-violet was found, confirming the modelling predictions and showing that the rational approach to materials design was successful. This Tyndall technology has now been licensed for further exploitation to Umicore.

Impulse Generator Microchip Design and Implementation

Researchers in the Circuits and Systems group have won the race to demonstrate the implementation of an efficient ultra-wide-band (UWB) monocycle pulse generator that is fully integrated in 90nm CMOS technology. The circuit, designed and realized by Stokes lecturer Domenico Zito, was presented at the IEEE International Solid-State Circuit Conference in San Francisco in February 2011, the world-wide top conference both for industry and academia in this field.  This ground-breaking microchip provides very short radio pulses by exploiting the operating principle of nonlinear waveform shapers. It produces monocycle pulses with the highest reported peak-to-peak voltage and energy efficiency in standard silicon technology: the device is 30 times more efficient than the best solution currently available. This makes it possible to implement radar sensors on silicon chips for longer range detection and to download data wirelessly from the internet over longer distances. Commercial avenues for exploitation are now being explored.

 


Monocycle pulse provided by the pulse generator.

Energy efficient electronics

Energy efficiency is key in the design of handheld electronic devices. Prof. Peter Kennedy in the Circuit and Systems group is addressing the design of key electronic components to achieve this aim. Digital delta-sigma modulators (DDSMs) are used in mobile phones and consumer audio systems. Prof. Kennedy’s group has developed a method for reducing the power consumption of DDSMs. Traditional DDSMs use a cascade of digital subcircuits that are all the same size. We have shown a route to reducing the sizes of successive subcircuits, thereby cutting the overall cost and power consumption by 20% relative to existing solutions with no degradation in performance.

Injection-locked frequency dividers (ILFDs) are becoming more popular in wireless communication systems to control frequency selection. One of the problems with ILFDs is how to make them lock over as wide a range of frequencies as possible. Kennedy’s group has developed a design methodology for ILFDs which solves this problem, and is expected to make it easier to design future high performance microchips for wireless applications.

Energy Efficient Electronics: Energy efficient MASH DDSM. The three modulators have successively fewer bit busses.

 

Engineering LED Light Sources across a wide spectral range

Work by Stefan Schulz and Eoin O’Reilly in photonics theory has identified the benefits of gallium nitride quantum dots to extend the range of efficient LED light emission into new wavelength ranges, including efficient ultra-violet and amber emission. Gallium nitride (GaN) has enabled the introduction of blue light lasers and efficient blue and green LEDs. There are numerous applications in display technology, medical diagnostics and lifesciences that would benefit from efficient emission over a wider wavelength range. However, a major challenge to extending the emission wavelength range is the presence of large built-in polarisation fields due to the GaN crystal structure. Schulz and colleagues have shown that, due to dot size and strain relaxation, the built-in potential 


Improved carrier overlap and recombination efficiency in a GaN quantum dot.

Optical Synthesis of Terahertz and mm-Wave Frequencies

Stephen O’Brien and colleagues in Photonics Theory have designed and demonstrated passively mode-locked discrete mode (DM) lasers that generate both sinusoidal and pulsed intensity output with modulation frequencies from 100 - 160 GHz. These results are based on technology that has been licensed to Eblana Photonics and indicate that DM lasers have significant potential as ultrastable sources for a wide range of applications. These include wide-bandwidth, wireless communications, optical sampling and THz generation by photo-mixing.


Examples of the rich dynamical behaviour observed in optical injection experiments of two-colour DM lasers.

Contact: 

Mary O'Regan mary.oregan@tyndall.ie
Theory Centre Administrator

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