Douglas J. Paul

Bio: Douglas J. Paul is an academic researcher from University of Glasgow. The author has contributed to research in topics: Quantum well & Silicon. The author has an hindex of 35, co-authored 306 publications receiving 4804 citations. Previous affiliations of Douglas J. Paul include University of Cambridge.

Si/SiGe heterostructures: from material and physics to devices and circuits

Abstract: Silicon germanium (SiGe) has moved from being a research material to accounting for a small but significant percentage of manufactured semiconductor devices. This percentage is predicted to increase substantially as SiGe begins to be used in complementary metal oxide semiconductor (CMOS) technology in the future to substantially improve performance. It is the development of Si/SiGe heterostructures which has enabled band structure and strain engineering allowing Si/SiGe to be used in many different ways to improve conventional microelectronic device performance along with allowing new concepts to be explored. This paper presents a review of the material properties, growth techniques, band structure and the main electronic devices of the Si/SiGe heterostructure system. In particular, the important device technologies in mainstream microelectronics of the SiGe heterostructure bipolar transistor (HBT) and strained-Si CMOS will be reviewed before future device and optoelectronics concepts are explored.

Design and fabrication of memory devices based on nanoscale polyoxometalate clusters

Abstract: Flash memories are essential for modern electronics; here a selenium-templated polyoxometalate is used to engineer new metal–oxide–semiconductor devices. Flash memory is becoming standard for smart phones, cameras, memory sticks and other devices. Its achievable data storage densities are ultimately limited by the minimum size of the individual data cells that can be fabricated, so molecule-based flash memory is an attractive proposition for stretching these limits. Christoph Busche and colleagues report the design, synthesis and electronic characterization of a family of metal-oxide cluster molecules that are compatible with current technology. The new materials are highly configurable at the atomic-level and show promise for implementation in practical devices. Flash memory devices—that is, non-volatile computer storage media that can be electrically erased and reprogrammed—are vital for portable electronics, but the scaling down of metal–oxide–semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory1, but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory2, there are a number of significant barriers to the realization of devices using conventional MOS technologies3,4,5,6,7. Here we show that core–shell polyoxometalate (POM) molecules8 can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core–shell POM clusters, we show, at both the molecular and device level, that embedding [(Se(iv)O3)2]4− as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se(v)2O6]2− moiety containing a {Se(v)–Se(v)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call ‘write-once-erase’. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour9,10,11. This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit12.

Measurement of the Earth tides with a MEMS gravimeter

Abstract: The ability to measure tiny variations in the local gravitational acceleration allows, besides other applications, the detection of hidden hydrocarbon reserves, magma build-up before volcanic eruptions, and subterranean tunnels. Several technologies are available that achieve the sensitivities required for such applications (tens of microgal per hertz1/2): free-fall gravimeters1, spring-based gravimeters1, 3, superconducting gravimeters4, and atom interferometers5. All of these devices can observe the Earth tides6: the elastic deformation of the Earth’s crust as a result of tidal forces. This is a universally predictable gravitational signal that requires both high sensitivity and high stability over timescales of several days to measure. All present gravimeters, however, have limitations of high cost (more than 100,000 US dollars) and high mass (more than 8 kilograms). Here we present a microelectromechanical system (MEMS) device with a sensitivity of 40 microgal per hertz1/2 only a few cubic centimetres in size. We use it to measure the Earth tides, revealing the long-term stability of our instrument compared to any other MEMS device. MEMS accelerometers—found in most smart phones7—can be mass-produced remarkably cheaply, but none are stable enough to be called a gravimeter. Our device has thus made the transition from accelerometer to gravimeter. The small size and low cost of this MEMS gravimeter suggests many applications in gravity mapping. For example, it could be mounted on a drone instead of low-flying aircraft for distributed land surveying and exploration, deployed to monitor volcanoes, or built into multi-pixel density-contrast imaging arrays.

Midinfrared Plasmon-Enhanced Spectroscopy with Germanium Antennas on Silicon Substrates

Abstract: Midinfrared plasmonic sensing allows the direct targeting of unique vibrational fingerprints of molecules. While gold has been used almost exclusively so far, recent research has focused on semiconductors with the potential to revolutionize plasmonic devices. We fabricate antennas out of heavily doped Ge films epitaxially grown on Si wafers and demonstrate up to 2 orders of magnitude signal enhancement for the molecules located in the antenna hot spots compared to those located on a bare silicon substrate. Our results set a new path toward integration of plasmonic sensors with the ubiquitous CMOS platform.

Silicon‐Germanium Strained Layer Materials in Microelectronics

Abstract: Review: The use of Si1–xGex in microelectronics production is appealing not only because it is compatible with existing industrial technology used for the production of silicon‐based microelectronics, but also because the induced strain caused by insertion of a layer of Si1–xGex(see Figure) can significantly improve their performance. The production and properties of these new materials are reviewed.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The Observation of Gravitational Waves from a Binary Black Hole Merger

Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

The Past, Present, and Future of Silicon Photonics

Abstract: The pace of the development of silicon photonics has quickened since 2004 due to investment by industry and government. Commercial state-of-the-art CMOS silicon-on-insulator (SOI) foundries are now being utilized in a crucial test of 1.55-mum monolithic optoelectronic (OE) integration, a test sponsored by the Defense Advanced Research Projects Agency (DARPA). The preliminary results indicate that the silicon photonics are truly CMOS compatible. RD however, lasing has not yet been attained. The new paradigm for the Si-based photonic and optoelectric integrated circuits is that these chip-scale networks, when suitably designed, will operate at a wavelength anywhere within the broad spectral range of 1.2-100 mum, with cryocooling needed in some cases

Zr-based metal-organic frameworks: design, synthesis, structure, and applications.

Abstract: Among the large family of metal–organic frameworks (MOFs), Zr-based MOFs, which exhibit rich structure types, outstanding stability, intriguing properties and functions, are foreseen as one of the most promising MOF materials for practical applications. Although this specific type of MOF is still in its early stage of development, significant progress has been made in recent years. Herein, advances in Zr-MOFs since 2008 are summarized and reviewed from three aspects: design and synthesis, structure, and applications. Four synthesis strategies implemented in building and/or modifying Zr-MOFs as well as their scale-up preparation under green and industrially feasible conditions are illustrated first. Zr-MOFs with various structural types are then classified and discussed in terms of different Zr-based secondary building units and organic ligands. Finally, applications of Zr-MOFs in catalysis, molecule adsorption and separation, drug delivery, and fluorescence sensing, and as porous carriers are highlighted. Such a review based on a specific type of MOF is expected to provide guidance for the in-depth investigation of MOFs towards practical applications.