Deposition of c-axis orientation aluminum nitride films on flexible polymer substrates by reactive direct-current magnetron sputtering

Aluminum nitride (AlN) piezoelectric thin films with c-axis crystal orientation on polymer substrates can potentially be used for development of flexible electronics and lab-on-chip systems. In this study, we investigated the effects of deposition parameters on the crystal structure of AlN thin films on polymer substrates deposited by reactive direct-current magnetron sputtering. The results show that low sputtering pressure as well as optimized N 2/Ar flow ratio and sputtering power is beneficial for AlN (002) orientation and can produce a highly (002) oriented columnar structure on polymer substrates. High sputtering power and low N 2/Ar flow ratio increase the deposition rate. In addition, the thickness of Al underlayer also has a strong influence on the film crystallography. The optimal deposition parameters in our experiments are: deposition pressure 0.38 Pa, N 2/Ar flow ratio 2:3, sputtering power 414 W, and thickness of Al underlayer less than 100 nm. © 2012 Elsevier B.V. All rights reserved.

Local synthesis and alignment of zinc oxide nanowires in aqueous solution using microheaters

A bottom-up technique for synthesizing transversely suspended zinc oxide nanowires (ZnO NWs) under a zinc nitrate (Zn(NO 3) 2· 6H 2O) and hexamethylenetetramine (HMTA, (CH 2) 6·N 4) solution within a microfabricated device is reported in this paper. The device consists of a microheater which is used to initially create an oxidized ZnO seed layer. ZnO NWs are then locally synthesized by the microheater and electrodes embedded within the devices are used to drive electric field directed horizontal alignment of the nanowires within the device. The entire process is carried out at low temperature. This approach has the potential to considerably simplify the fabrication and assembly of ZnO nanowires on CMOS compatible substrates, allowing for the chemical synthesis to be carried out under near-ambient conditions by locally defining the conditions for nanowire growth on a silicon reactor chip. © 2012 IEEE.

Active-passive 44 SOA-based switch with integrated power monitoring

The first monolithically integrated 44 switch with power monitoring function using on-chip PIN photodiodes is reported. Using 10Gb/s signals, under active power control an IPDR of 12dB for a 1dB power penalty is achieved. © 2012 OSA.

Ferroelectric liquid crystal mixture integrated into optical waveguides

We report an on-chip integrated ferroelectric liquid crystal (FLC) waveguide structure suitable for telecommunication applications. Single gaps with different widths of 5, 10, and 20 μ m inside individual silica waveguides were filled with an FLC mixture. The waveguide devices operate as a binary switch or an attenuator in a temperature range from 30 °C to 60 °C. The FLC mixture exhibited a good alignment quality in these gaps without alignment layers. A good extinction ratio of up to 33.9 dB and a low insertion loss of <4.3 dB at λ = 1550 nm were observed. Switching times of <100 μs were obtained for the low electric fields applied in this experiment. © 2012 IEEE.

Bayesian correlated clustering to integrate multiple datasets.

MOTIVATION: The integration of multiple datasets remains a key challenge in systems biology and genomic medicine. Modern high-throughput technologies generate a broad array of different data types, providing distinct-but often complementary-information. We present a Bayesian method for the unsupervised integrative modelling of multiple datasets, which we refer to as MDI (Multiple Dataset Integration). MDI can integrate information from a wide range of different datasets and data types simultaneously (including the ability to model time series data explicitly using Gaussian processes). Each dataset is modelled using a Dirichlet-multinomial allocation (DMA) mixture model, with dependencies between these models captured through parameters that describe the agreement among the datasets. RESULTS: Using a set of six artificially constructed time series datasets, we show that MDI is able to integrate a significant number of datasets simultaneously, and that it successfully captures the underlying structural similarity between the datasets. We also analyse a variety of real Saccharomyces cerevisiae datasets. In the two-dataset case, we show that MDI's performance is comparable with the present state-of-the-art. We then move beyond the capabilities of current approaches and integrate gene expression, chromatin immunoprecipitation-chip and protein-protein interaction data, to identify a set of protein complexes for which genes are co-regulated during the cell cycle. Comparisons to other unsupervised data integration techniques-as well as to non-integrative approaches-demonstrate that MDI is competitive, while also providing information that would be difficult or impossible to extract using other methods.

Predictive control of a Boeing 747 aircraft using an FPGA

New embedded predictive control applications call for more eficient ways of solving quadratic programs (QPs) in order to meet demanding real-time, power and cost requirements. A single precision QP-on-a-chip controller is proposed, implemented in afield-programmable gate array (FPGA) with an iterative linear solver at its core. A novel offline scaling procedure is introduced to aid the convergence of the reduced precision solver. The feasibility of the proposed approach is demonstrated with a real-time hardware-in-the-loop (HIL) experimental setup where an ML605 FPGA board controls a nonlinear model of a Boeing 747 aircraft running on a desktop PC through an Ethernet link. Simulations show that the quality of the closed-loop control and accuracy of individual solutions is competitive with a conventional double precision controller solving linear systems using a Riccati recursion. © 2012 IFAC.

Film bulk acoustic resonator pressure sensor with self temperature reference

A novel film bulk acoustic resonator (FBAR) with two resonant frequencies which have opposite reactions to temperature changes has been designed. The two resonant modes respond differently to changes in temperature and pressure, with the frequency shift being linearly correlated with temperature and pressure changes. By utilizing the FBAR's sealed back trench as a cavity, an on-chip single FBAR sensor suitable for measuring pressure and temperature simultaneously is proposed and demonstrated. The experimental results show that the pressure coefficient of frequency for the lower frequency peak of the FBAR sensors is approximately -17.4 ppm kPa-1, while that for the second peak is approximately -6.1 ppm kPa-1, both of them being much more sensitive than other existing pressure sensors. This dual mode on-chip pressure sensor is simple in structure and operation, can be fabricated at very low cost, and yet requires no specific package, therefore has great potential for applications. © 2012 IOP Publishing Ltd.

SOI CMOS integrated zinc oxide nanowire for toluene detection

The paper reports on the in-situ growth of zinc oxide nanowires (ZnONWs) on a complementary metal oxide semiconductor (CMOS) substrate, and their performance as a sensing element for ppm (parts per million) levels of toluene vapour in 3000 ppm humid air. Zinc oxide NWs were grown using a low temperature (only 90°C) hydrothermal method. The ZnONWs were first characterised both electrically and through scanning electron microscopy. Then the response of the on-chip ZnONWs to different concentrations of toluene (400-2600ppm) was observed in air at 300°C. Finally, their gas sensitivity was determined and found to lie between 0.1% and 0.3% per ppm. © 2013 IEEE.

Energy recycling from multigigahertz clocks using fully integrated switching converters

Large digital chips use a significant amount of energy to broadcast a low-skew, multigigahertz clock to millions of latches located throughout the chip. Every clock cycle, the large aggregate capacitance of the clock network is charged from the supply and then discharged to ground. Instead of wasting this stored energy, it is possible to recycle the energy by controlling its delivery to another part of the chip using an on-chip dc-dc converter. The clock driver and switching converter circuits share many compatible characteristics that allow them to be merged into a single design and fully integrated on-chip. Our buck converter prototype, manufactured in 90-nm CMOS, provides a proof-of-concept that clock network energy can be recycled to other parts of the chip, thus lowering overall energy consumption. It also confirms that monolithic multigigahertz switching converters utilizing zero-voltage switching can be implemented in deep-submicrometer CMOS. With multigigahertz operation, fully integrated inductors and capacitors use a small amount of chip area with low losses. Combining the clock driver with the power converter can share the large MOSFET drivers necessary as well as being energy and space efficient. We present an analysis of the losses which we confirm by experimentally comparing the merged circuit with a conventional clock driver. © 2012 IEEE.

Characterization and fabrication of zinc oxide nanowire devices

In this paper, we demonstrate an approach for the local synthesis of ZnO nanowires (ZnO NWs) and the potential for such structures to be incorporated into device applications. Three network ZnO NW devices are fabricated on a chip by using a bottom-up synthesis approach. Microheaters (defined by standard semiconductor processing) are used to synthesize the ZnO NWs under a zinc nitrate (Zn(NO3)2·6H2O) and hexamethylenetetramine (HMTA, (CH2)6·N4) solution. By controlling synthesis parameters, varying densities of networked ZnO NWs are locally synthesized on the chip. The fabricated networked ZnO NW devices are then characterized using UV excitation and cyclic voltammetry (CV) experiments to measure their photoresponse and electrochemical properties. The experimental results show that the techniques and material systems presented here have the potential to address interesting device applications using fabrication methods that are fully compatible with standard semiconductor processing. © 2013 IEEE.

Fabrication, densification, and replica molding of 3D carbon nanotube microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, labon- a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1,2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3. © 2012 Journal of Visualized Experiments.

Fabrication of high-aspect-ratio polymer microstructures and hierarchical textures using carbon nanotube composite master molds

Scalable and cost effective patterning of polymer structures and their surface textures is essential to engineer material properties such as liquid wetting and dry adhesion, and to design artificial biological interfaces. Further, fabrication of high-aspect-ratio microstructures often requires controlled deep-etching methods or high-intensity exposure. We demonstrate that carbon nanotube (CNT) composites can be used as master molds for fabrication of high-aspect-ratio polymer microstructures having anisotropic nanoscale textures. The master molds are made by growth of vertically aligned CNT patterns, capillary densification of the CNTs using organic solvents, and capillary-driven infiltration of the CNT structures with SU-8. The composite master structures are then replicated in SU-8 using standard PDMS transfer molding methods. By this process, we fabricated a library of replicas including vertical micro-pillars, honeycomb lattices with sub-micron wall thickness and aspect ratios exceeding 50:1, and microwells with sloped sidewalls. This process enables batch manufacturing of polymer features that capture complex nanoscale shapes and textures, while requiring only optical lithography and conventional thermal processing. © 2011 The Royal Society of Chemistry.

Predictive control using an FPGA with application to aircraft control

Alternative and more efficient computational methods can extend the applicability of model predictive control (MPC) to systems with tight real-time requirements. This paper presents a system-on-a-chip MPC system, implemented on a field-programmable gate array (FPGA), consisting of a sparse structure-exploiting primal dual interior point (PDIP) quadratic program (QP) solver for MPC reference tracking and a fast gradient QP solver for steady-state target calculation. A parallel reduced precision iterative solver is used to accelerate the solution of the set of linear equations forming the computational bottleneck of the PDIP algorithm. A numerical study of the effect of reducing the number of iterations highlights the effectiveness of the approach. The system is demonstrated with an FPGA-in-the-loop testbench controlling a nonlinear simulation of a large airliner. This paper considers many more manipulated inputs than any previous FPGA-based MPC implementation to date, yet the implementation comfortably fits into a midrange FPGA, and the controller compares well in terms of solution quality and latency to state-of-the-art QP solvers running on a standard PC. © 1993-2012 IEEE.

Sensors based on SAW and FBAR technologies

Over the last few years a number of sensing platforms are being investigated for their use in drug development, microanalysis or medical diagnosis. Lab-on-a-chip (LOC) are devices integrating more than one laboratory functions on a single device chip of a very small size, and typically consist of two main components: microfluidic handling systems and sensors. The physical mechanisms that are generally used for microfluidics and sensors are different, hence making the integration of these components difficult and costly. In this work we present a lab-on-a-chip system based on surface acoustic waves (for fluid manipulation) and film bulk acoustic resonators (for sensing). Coupling surface acoustic waves into liquids induces acoustic streaming and motion of micro-droplets, whilst it is well-known that bulk acoustic waves can be used to fabricate microgravimetric sensors. Both technologies offer exceptional sensitivity and can be fabricated from piezoelectric thin films deposited on Si substrates, reducing the fabrication time/cost of the LOC devices. © 2013 SPIE.

A single FBAR-based temperature and pressure sensors

A novel temperature and pressure sensor based on a single film bulk acoustic resonator (FBAR) is designed. This FBAR support two resonant modes, which response opposite to the change of temperature. By sealed the back cavity of a back-trench membrane type FBAR with silicon wafer, an on-chip single FBAR sensor suitable for measuring temperature and pressure simultaneously is proposed. For unsealed device, the experimental results show that the first resonant mode has a temperature coefficient of frequency (TCF) of 69.5ppm/K, and the TCF of the second mode is -8.1ppm/K. After sealed the back trench, it can be used as a pressure sensor, the pressure coefficient of frequency (PCF) for the two resonant mode is -17.4ppm/kPa and -6.1 ppm/kPa respectively, both of them being more sensitive than other existing pressure sensors. © 2013 Trans Tech Publications Ltd, Switzerland.