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  • 29451.
    Özkan, Emre
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Lundquist, Christian
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Bayesian Approach to Jointly Estimate Tire Radii and Vehicle Trajectory2011Inngår i: Proceedings of the International IEEE Conference on Intelligent Transportation Systems, Washington DC, USA: IEEE conference proceedings, 2011, s. 1-6Konferansepaper (Fagfellevurdert)
    Abstract [en]

    High-precision estimation of vehicle tire radii is considered, based on measurements on individual wheel speeds and absolute position from a global navigation satellite system (GNSS). The wheel speed measurements are subject to noise with time-varying covariance that depends mainly on the road surface. The novelty lies in a Bayesian approach to estimate online the time-varying radii and noise parameters using a marginalized particle filter, where no model approximations are needed such as in previously proposed algorithms based on the extended Kalman filter. Field tests show that the absolute radius can be estimated with millimeter accuracy, while the relative wheel radius on one axle is estimated with submillimeter accuracy.

    Fulltekst (pdf)
    fulltext
  • 29452.
    Özkan, Emre
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Saha, Saikat
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Smidl, Vaclav
    Institute of Information Theory and Automation, Czech Repbulic.
    Non-Parametric Bayesian Measurement Noise Density Estimation in Non-Linear Filtering2011Inngår i: Acoustics, Speech and Signal Processing (ICASSP), 2011, IEEE , 2011, s. 5924-5927Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this study, we investigate online Bayesian estimation of the measurement noise density of a given state space model using particle filters and Dirichlet process mixtures. Dirichlet processes are widely used in statistics for nonparametric density estimation. In the proposed method, the unknown noise is modeled as a Gaussian mixture with unknown number of components. The joint estimation of the state and the noise density is done via particle filters. Furthermore, the number of components and the noise statistics are allowed to vary in time. An extension of the method for the estimation of time varying noise characteristics is also introduced.

  • 29453.
    Özkan, Emre
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Smidl, Vaclav
    Institute of Information Theory and Automation, Czech Republic.
    Saha, Saikat
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Lundquist, Christian
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Marginalized Adaptive Particle Filtering for Nonlinear Models with Unknown Time-Varying Noise Parameters2013Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 49, nr 6, s. 1566-1575Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Knowledge of the noise distribution is typically crucial for the state estimation of general state-space models. However, properties of the noise process are often unknown in the majority of practical applications. The distribution of the noise may also be non-stationary or state dependent and that prevents the use of off-line tuning methods. For linear Gaussian models, Adaptive Kalman filters (AKF) estimate unknown parameters in the noise distributions jointly with the state. For nonlinear models, we provide a Bayesian solution for the estimation of the noise distributions in the exponential family, leading to a marginalized adaptive particle filter (MAPF) where the noise parameters are updated using finite dimensional sufficient statistics for each particle. The time evolution model for the noise parameters is defined implicitly as a Kullback-Leibler norm constraint on the time variability, leading to an exponential forgetting mechanism operating on the sufficient statistics. Many existing methods are based on the standard approach of augmenting the state with the unknown variables and attempting to solve the resulting filtering problem. The MAPF is significantly more computationally efficient than a comparable particle filter that runs on the full augmented state. Further, the MAPF can handle sensor and actuator offsets as unknown means in the noise distributions, avoiding the standard approach of augmenting the state with such offsets. We illustrate the MAPF on first a standard example, and then on a tire radius estimation problem on real data.

  • 29454. Bestill onlineKjøp publikasjonen >>
    Čirkić, Mirsad
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Efficient MIMO Detection Methods2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    For the past decades, the demand in transferring large amounts of data rapidly and reliably has been increasing drastically. One of the more promising techniques that can provide the desired performance is multiple-input multiple-output (MIMO) technology where multiple antennas are placed at both the transmitting and receiving side of the communication link. This performance potential is extremely high when the dimensions of the MIMO system are increased to an extreme (in the number of hundreds or thousands of antennas). One major implementation difficulty of the MIMO technology is the signal separation (detection) problem at the receiving side of the MIMO link, which holds for medium-size MIMO systems and even more so for large-size systems. This is due to the fact that the transmitted signals interfere with each other and that separating them can be very difficult if the MIMO channel conditions are not beneficial, i.e., the channel is not well-conditioned.

    The main problem of interest is to develop algorithms for practically feasible MIMO implementations without sacrificing the promising performance potential that such systems bring. These methods involve inevitably different levels of approximation. There are computationally cheap methods that come with low accuracy and there are computationally expensive methods that come with high accuracy. Some methods are more applicable in medium-size MIMO than in large-size MIMO and vice versa. Some simple methods for instance, which are typically inaccurate for medium-sized settings, can achieve optimal accuracy for certain large-sized settings that offer close-to-orthogonal spatial signatures. However, when the dimensions are overly increased, then even these (previously) simple methods become computationally burdensome. In different MIMO setups, the difficulty in detection shifts since methods with optimal accuracy are not the same. Therefore, devising one single algorithm which is well-suited for feasible MIMO implementations in all settings is not easy.

    This thesis addresses the general MIMO detection problem in two ways. One part treats a development of new and more efficient detection techniques for the different MIMO settings. The techniques that are proposed in this thesis demonstrate unprecedented performance in many relevant cases. The other part revolves around utilizing already proposed detection algorithms and their advantages versus disadvantages in an adaptive manner. For well-conditioned channels, low-complexity detection methods are often sufficiently accurate. In such cases, performing computationally very expensive optimal detection would be a waste of computational power. This said, for MIMO detection in a coded system, there is always a trade-off between performance and complexity. Intuitively, computational resources should be utilized more efficiently by performing optimal detection only when it is needed, and something simpler when it is not. However, it is not clear whether this is true or not. In trying to answer this, a general framework for adaptive computational-resource allocation to different (“simple” and “difficult”) detection problems is proposed. This general framework is applicable to any MIMO detector and scenario of choice, and it is exemplified using one particular detection method for which specific allocation techniques are developed and evaluated.

    Delarbeid
    1. Allocation of Computational Resources for Soft MIMO Detection
    Åpne denne publikasjonen i ny fane eller vindu >>Allocation of Computational Resources for Soft MIMO Detection
    2011 (engelsk)Inngår i: IEEE Journal of Selected Topics in Signal Processing, ISSN 1932-4553, Vol. 5, nr 8, s. 1451-1461Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We consider soft MIMO detection for the case of block fading. That is, the transmitted codeword spans over several independent channel realizations and several instances of the detection problem must be solved for each such realization. We develop methods that adaptively allocate computational resources to the detection problems of each channel realization, under a total per-codeword complexity constraint. Our main results are a formulation of the problem as a mathematical optimization problem with a well-defined objective function and constraints, and algorithms that solve this optimization problem efficiently computationally.

    sted, utgiver, år, opplag, sider
    IEEE conference proceedings, 2011
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-69612 (URN)10.1109/JSTSP.2011.2162719 (DOI)000297348500006 ()
    Merknad
    ©2011 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Mirsad Čirkić, Daniel Persson and Erik G. Larsson, Allocation of Computational Resources for Soft MIMO Detection, 2011, accepted IEEE Journal of Selected Topics in Signal Processing Tilgjengelig fra: 2011-07-06 Laget: 2011-07-06 Sist oppdatert: 2016-08-31
    2. Approximating the LLR Distribution for a Class of Soft-Output MIMO Detectors
    Åpne denne publikasjonen i ny fane eller vindu >>Approximating the LLR Distribution for a Class of Soft-Output MIMO Detectors
    2012 (engelsk)Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, nr 12, s. 6421-6434Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We present approximations of the LLR distribution for a class of fixed-complexity soft-output MIMO detectors, such as the optimal soft detector and the soft-output via partial marginalization detector. More specifically, in a MIMO AWGN setting, we approximate the LLR distribution conditioned on the transmitted signal and the channel matrix with a Gaussian mixture model (GMM). Our main results consist of an analytical expression of the GMM model (including the number of modes and their corresponding parameters) and a proof that, in the limit of high SNR, this LLR distribution converges in probability towards a unique Gaussian distribution.

    sted, utgiver, år, opplag, sider
    Institute of Electrical and Electronics Engineers (IEEE), 2012
    Emneord
    Fixed-complexity sphere-decoder; Gaussian mixture model; LLR distribution; MIMO detection; partial marginalization
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-87205 (URN)10.1109/TSP.2012.2217336 (DOI)000311805000024 ()
    Merknad

    On the defence date of the Licentiate Thesis the status of this article was Manuscript and the title was Approximating the LLR Distribution for the Optimal and Partial Marginalization MIMO Detectors.

    Tilgjengelig fra: 2013-01-14 Laget: 2013-01-14 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    3. SUMIS: Near-Optimal Soft-In Soft-Out MIMO Detection with Low and Fixed Complexity
    Åpne denne publikasjonen i ny fane eller vindu >>SUMIS: Near-Optimal Soft-In Soft-Out MIMO Detection with Low and Fixed Complexity
    2014 (engelsk)Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 62, nr 12, s. 3084-3097Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The fundamental problem of interest here is soft-input soft-output multiple-input multiple-output (MIMO) detection. We propose a method, referred to as subspace marginalization with interference suppression (SUMIS), that yields unprecedented performance at low and fixed (deterministic) complexity. Our method provides a well-defined tradeoff between computational complexity and performance. Apart from an initial sorting step consisting of selecting channel-matrix columns, the algorithm involves no searching nor algorithmic branching; hence the algorithm has a completely predictable run-time and allows for a highly parallel implementation. We numerically assess the performance of SUMIS in different practical settings: full/partial channel state information, sequential/iterative decoding, and low/high rate outer codes. We also comment on how the SUMIS method performs in systems with a large number of transmit antennas.

    sted, utgiver, år, opplag, sider
    IEEE Signal Processing Society, 2014
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-103671 (URN)10.1109/TSP.2014.2303945 (DOI)000338122400005 ()
    Tilgjengelig fra: 2014-01-22 Laget: 2014-01-22 Sist oppdatert: 2017-12-06
    4. On the Complexity of Very Large Multi-User MIMO Detection
    Åpne denne publikasjonen i ny fane eller vindu >>On the Complexity of Very Large Multi-User MIMO Detection
    2014 (engelsk)Inngår i: 2014 IEEE 15th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE, IEEE Press, 2014, s. 55-59Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    This work discusses efficient techniques for detection in large-size multi-user multiple-input multiple-output (MIMO) systems that are highly overdetermined. We exemplify the application of conjugate gradient methods in the setup of our interest and compare its performance with respect to methods based on the Neumann series expansion. We bring to light some important insights on the performance versus complexity tradeoffs that have not been uplifted before.

    sted, utgiver, år, opplag, sider
    IEEE Press, 2014
    Serie
    IEEE International Workshop on Signal Processing Advances in Wireless Communications, ISSN 2325-3789
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-103672 (URN)10.1109/SPAWC.2014.6941316 (DOI)000348859000012 ()978-1-4799-4903-8 (ISBN)
    Konferanse
    IEEE 15th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
    Tilgjengelig fra: 2014-01-22 Laget: 2014-01-22 Sist oppdatert: 2016-09-13bibliografisk kontrollert
    Fulltekst (pdf)
    Efficient MIMO Detection Methods
    Download (pdf)
    omslag
  • 29455. Bestill onlineKjøp publikasjonen >>
    Čirkić, Mirsad
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Optimization of Computational Resources for MIMO Detection2011Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    For the past decades, the demand in transferring large amounts of data rapidly and reliably has been increasing drastically. One of the more promising techniques that can provide the desired performance is the multiple-input multiple-output (MIMO) technology where multiple antennas are placed at both the transmitting and receiving side of the communication link. One major implementation difficulty of the MIMO technology is the signal separation (detection) problem at the receiving side of the MIMO link. This is due to the fact that the transmitted signals interfere with each other and that separating them can be very difficult if the MIMO channel conditions are not beneficial, i.e., the channel is not well-conditioned.

    For well-conditioned channels, low-complexity detection methods are often sufficiently accurate. In such cases, performing computationally very expensive optimal detection would be a waste of computational power. This said, for MIMO detection in a coded system, there is always a trade-off between performance and complexity. The fundamental question is, can we save computational resources by performing optimal detection only when it is needed, and something simpler when it is not? This is the question that this thesis aims to answer. In doing so, we present a general framework for adaptively allocating computational resources to different (“simple” and“difficult”) detection problems. This general framework is applicable to any MIMO detector and scenario of choice, and it is exemplified using one particular detection method for which specific allocation techniques are developed and evaluated.

    Delarbeid
    1. Allocation of Computational Resources for Soft MIMO Detection
    Åpne denne publikasjonen i ny fane eller vindu >>Allocation of Computational Resources for Soft MIMO Detection
    2011 (engelsk)Inngår i: IEEE Journal of Selected Topics in Signal Processing, ISSN 1932-4553, Vol. 5, nr 8, s. 1451-1461Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We consider soft MIMO detection for the case of block fading. That is, the transmitted codeword spans over several independent channel realizations and several instances of the detection problem must be solved for each such realization. We develop methods that adaptively allocate computational resources to the detection problems of each channel realization, under a total per-codeword complexity constraint. Our main results are a formulation of the problem as a mathematical optimization problem with a well-defined objective function and constraints, and algorithms that solve this optimization problem efficiently computationally.

    sted, utgiver, år, opplag, sider
    IEEE conference proceedings, 2011
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-69612 (URN)10.1109/JSTSP.2011.2162719 (DOI)000297348500006 ()
    Merknad
    ©2011 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Mirsad Čirkić, Daniel Persson and Erik G. Larsson, Allocation of Computational Resources for Soft MIMO Detection, 2011, accepted IEEE Journal of Selected Topics in Signal Processing Tilgjengelig fra: 2011-07-06 Laget: 2011-07-06 Sist oppdatert: 2016-08-31
    2. Approximating the LLR Distribution for a Class of Soft-Output MIMO Detectors
    Åpne denne publikasjonen i ny fane eller vindu >>Approximating the LLR Distribution for a Class of Soft-Output MIMO Detectors
    2012 (engelsk)Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, nr 12, s. 6421-6434Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We present approximations of the LLR distribution for a class of fixed-complexity soft-output MIMO detectors, such as the optimal soft detector and the soft-output via partial marginalization detector. More specifically, in a MIMO AWGN setting, we approximate the LLR distribution conditioned on the transmitted signal and the channel matrix with a Gaussian mixture model (GMM). Our main results consist of an analytical expression of the GMM model (including the number of modes and their corresponding parameters) and a proof that, in the limit of high SNR, this LLR distribution converges in probability towards a unique Gaussian distribution.

    sted, utgiver, år, opplag, sider
    Institute of Electrical and Electronics Engineers (IEEE), 2012
    Emneord
    Fixed-complexity sphere-decoder; Gaussian mixture model; LLR distribution; MIMO detection; partial marginalization
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-87205 (URN)10.1109/TSP.2012.2217336 (DOI)000311805000024 ()
    Merknad

    On the defence date of the Licentiate Thesis the status of this article was Manuscript and the title was Approximating the LLR Distribution for the Optimal and Partial Marginalization MIMO Detectors.

    Tilgjengelig fra: 2013-01-14 Laget: 2013-01-14 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    Fulltekst (pdf)
    Optimization of Computational Resources for MIMO Detection
    Download (pdf)
    omslag
  • 29456.
    Čirkić, Mirsad
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Near-Optimal Soft-Output Fixed-Complexity MIMO Detection via Subspace Marginalization and Interference Suppression2012Inngår i: 2012 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP), IEEE Signal Processing Society, 2012, , s. 4s. 2805-2808Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The fundamental problem of our interest here is soft MIMO detection. We propose a method that yields excellent performance, atlow and at fixed (deterministic) complexity. Our method provides a well-defined tradeoff between computational complexity and performance. Apart from an initial step consisting of selecting columns,the algorithm involves no searching nor algorithmic branching; hence the algorithm has a completely predictable run-time, and it is readily and massively parallelizable.

    Fulltekst (pdf)
    fulltext
  • 29457.
    Čirkić, Mirsad
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    On the Complexity of Very Large Multi-User MIMO Detection2014Inngår i: 2014 IEEE 15th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE, IEEE Press, 2014, s. 55-59Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This work discusses efficient techniques for detection in large-size multi-user multiple-input multiple-output (MIMO) systems that are highly overdetermined. We exemplify the application of conjugate gradient methods in the setup of our interest and compare its performance with respect to methods based on the Neumann series expansion. We bring to light some important insights on the performance versus complexity tradeoffs that have not been uplifted before.

  • 29458.
    Čirkić, Mirsad
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    SUMIS: Near-Optimal Soft-In Soft-Out MIMO Detection with Low and Fixed Complexity2014Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 62, nr 12, s. 3084-3097Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fundamental problem of interest here is soft-input soft-output multiple-input multiple-output (MIMO) detection. We propose a method, referred to as subspace marginalization with interference suppression (SUMIS), that yields unprecedented performance at low and fixed (deterministic) complexity. Our method provides a well-defined tradeoff between computational complexity and performance. Apart from an initial sorting step consisting of selecting channel-matrix columns, the algorithm involves no searching nor algorithmic branching; hence the algorithm has a completely predictable run-time and allows for a highly parallel implementation. We numerically assess the performance of SUMIS in different practical settings: full/partial channel state information, sequential/iterative decoding, and low/high rate outer codes. We also comment on how the SUMIS method performs in systems with a large number of transmit antennas.

  • 29459.
    Čirkić, Mirsad
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Persson, Daniel
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Allocation of Computational Resources for Soft MIMO Detection2011Inngår i: IEEE Journal of Selected Topics in Signal Processing, ISSN 1932-4553, Vol. 5, nr 8, s. 1451-1461Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider soft MIMO detection for the case of block fading. That is, the transmitted codeword spans over several independent channel realizations and several instances of the detection problem must be solved for each such realization. We develop methods that adaptively allocate computational resources to the detection problems of each channel realization, under a total per-codeword complexity constraint. Our main results are a formulation of the problem as a mathematical optimization problem with a well-defined objective function and constraints, and algorithms that solve this optimization problem efficiently computationally.

    Fulltekst (pdf)
    fulltext
  • 29460.
    Čirkić, Mirsad
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Persson, Daniel
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    New Results on Adaptive Computational Resource Allocation in Soft MIMO Detection2011Inngår i: Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), IEEE conference proceedings, 2011, s. 2972-2975Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The fundamental problem of our interest is soft MIMO detection for  the case of block fading, i.e., when the transmitted codeword spans  over several independent channel realizations. We develop methods  that adaptively allocate computational resources to the detection  problems of each channel realization, under a total per-codeword  complexity constraint. The new results consist of a new algorithm, a  new performance measure, and a thorough complexity discussion.

  • 29461.
    Čirkić, Mirsad
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Persson, Daniel
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Optimization of Computational Resource Allocation for Soft MIMO Detection2009Inngår i: Proceedings of the 43rd Asilomar Conference on Signals, Systems, and Computers (ACSSC'09), IEEE , 2009, s. 1488-1492Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider soft MIMO detection for the case of block fading. That is, the transmitted codeword spans over several independent channel realizations and several instances of the detection problem must be solved for each such realization. We develop methods that adaptively allocate the computational resources to the detection problems of each channel realization, under a total per-codeword complexity constraint. Our main results are a formulation of the problem as a mathematical optimization problem and a greedy algorithm to approximate it in a computationally feasible fashion.

  • 29462.
    Čirkić, Mirsad
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Persson, Daniel
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Jan-Åke
    Linköpings universitet, Institutionen för systemteknik, Informationskodning. Linköpings universitet, Tekniska högskolan.
    Gaussian Approximation of the LLR Distribution for the ML and Partial Marginalization MIMO detectors2011Inngår i: Proceedings of the IEEE International Conference on Acoustics, Speech and SignalProcessing (ICASSP), IEEE conference proceedings, 2011, s. 3232-3235Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We derive a Gaussian approximation of the LLR distribution  conditioned on the transmitted signal and the channel matrix for the  soft-output via partial marginalization MIMO detector. This detector  performs exact ML as a special case. Our main results consist of  discussing the operational meaning of this approximation and a proof  that, in the limit of high SNR, the LLR distribution of interest  converges in probability towards a Gaussian distribution.

  • 29463.
    Šmídl, Václav
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Forgetting in Marginalized Particle Filtering and its Relation to Forward Smoothing2011Rapport (Annet vitenskapelig)
    Abstract [en]

    The problem of degeneracy in marginalized particle filtering is addressed. In particular, we note that the degeneracy is caused by loss of entropy of the posterior distribution and design maximum entropy estimates to prevent this. The main technique used in this report is known as forgetting. Itis shown that it can be used to suppress the problem with degeneracy, however, it is not a proper cure for the problem of stationary parameters. The problem of marginal-marginalized particle filter for sufficient statistics is also studied. The resulting algorithm is found to have remarkable similarities with the algorithm known as forward smoothing.

    Fulltekst (pdf)
    FULLTEXT01
  • 29464.
    Ščajev, Patrik
    et al.
    Institute of Applied Research, Vilnius University, Vilnius, Lithuania.
    Hassan, Jawad
    Institute of Applied Research, Vilnius University, Vilnius, Lithuania.
    Jarašiūnas, Kęstutis
    Institute of Applied Research, Vilnius University, Vilnius, Lithuania.
    Kato, Masashi
    Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya, Japan.
    Henry, Anne
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Bergman, J Peder
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Comparative Studies of Carrier Dynamics in 3C-SiC Layers Grown on Si and 4H-SiC Substrates2011Inngår i: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 40, nr 4, s. 394-399Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Time-resolved nonlinear optical techniques were applied to determine the electronic parameters of cubic silicon carbide layers. Carrier lifetime, tau, and mobility, mu, were measured in a free-standing wafer grown on undulant Si and an epitaxial layer grown by hot-wall chemical vapor deposition (CVD) on a nominally on-axis 4H-SiC substrate. Nonequilibrium carrier dynamics was monitored in the 80 K to 800 K range by using a picosecond free carrier grating and free carrier absorption techniques. Correlation of tau(T) and mu (a)(T) dependencies was explained by the strong contribution of diffusion-limited recombination on extended defects in the layers. A lower defect density in the epitaxial layer on 4H-SiC was confirmed by a carrier lifetime of 100 ns, being similar to 4 times longer than that in free-standing 3C.

  • 29465.
    Žitinski Elías, Paula
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Halftoning for Multi-Channel Printing: Algorithm Development, Implementation and Verification2014Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    A seemingly straightforward way to enhance the quality of printed images is to increase the number of colorants, beyond the four traditionally used, in multi-channel printing. Potential improvements to reproduced images include: increased colour accuracy, enhanced colour smoothness and reduced image graininess. Nevertheless, numerous challenges exist, one of them being the implementation of halftoning algorithms, which transform the original image into a binary one that is reproducible by the printing system. This thesis concerns the development, implementation and verification of halftoning algorithms suitable for an increased number of colorants in multi-channel printing.

    The first focus in this thesis is on the implementation of an amplitude modulated (AM) halftoning method for seven-channel printing utilizing CMYKRGB colorants. The proposed AM halftoning method utilizes non-orthogonal halftone screens instead of orthogonal ones (dots), thus enabling a wider angle range for the channels that makes possible to accommodate multi-channel impressions. The performance of the non-orthogonal halftoning method was evaluated by computational simulation of channel misregistration for 1600 different scenarios and assessment of printed orthogonal and non-orthogonal patches. The simulated and printed results demonstrate that the proposed halftoning method utilizing non-orthogonal screens shows no visible moiré and produces smaller colour shifts in case of misregistration when compared to orthogonal halftoning.

    However, the layer thickness of the combined colorants is not controlled by the aforementioned multi-channel AM halftoning approach. Therefore, the second focus in this thesis concerns the adjustment and implementation of a multilevel halftoning algorithm for achromatic and chromatic inks. In this algorithm, a channel is processed so that it can be printed using multiple inks of same hue value, achieving a single ink layer. Here, the thresholds for ink separation and dot gain compensation pose an interesting challenge. Since dot gain originates from the interaction between a specific ink and specific paper, compensating the original image for multilevel halftoning means expressing the dot gain of multiple inks in terms of the nominal coverage of a single ink. The applicability of the proposed multilevel halftoning workflow is demonstrated using multiple inks while avoiding dot-on-dot placement and accounting for dot gain. The results also show that the multilevel halftoned image is visually improved in terms of graininess and detailenhancement when compared to a bi-level halftoned image.

    Fulltekst (pdf)
    Halftoning for Multi-Channel Printing: Algorithm Development, Implementation and Verification
    Download (pdf)
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    presentationsbild
  • 29466. Bestill onlineKjøp publikasjonen >>
    Žukauskaitė, Agnė
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Metastable ScAlN and YAlN Thin Films Grown by Reactive Magnetron Sputter Epitaxy2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Metastable ScxAl1-xN and YxAl1-xN thin films were deposited in an ultra high vacuum system using reactive magnetron sputter epitaxy from elemental Al, Sc, and Y targets in Ar/N2 gas mixture. Their structural, electrical, optical, mechanical, and piezoelectrical properties were investigated by using the transmission electron microscopy, x-ray diffraction, spectroscopic ellipsometry, I-V and C-V measurements, nanoindentation, and two different techniques for piezoelectric characterization: piezoresponse force microscopy and double beam interferometry.

    Compared to AlN, improved electromechanical coupling and increase in piezoelectric response was found in ScxAl1-xN/TiN/Al2O3 structures with Sc content up to x=0.2. Decreasing the growth temperature down to 400 °C improved the microstructure and crystalline quality of the material. Microstructure of the films had a stronger influence on piezoelectric properties than the crystalline quality, which affected the leakage currents. When x was increased from x=0 to x=0.3, the hardness and reduced Young’s modulus Er showed a decrease from 17 GPa to 11 GPa, and 265 GPa down to 224 GPa, respectively. In ScxAl1-xN/InyAl1-yN superlattices, ScxAl1-xN layers negative lattice mismatched to In-rich InyAl1-yN were found to be stable at higher Sc concentration (x=0.4) than lattice-matched or positive lattice mismatched layers, confirmed by first principle (ab initio) calculations using density-functional formalism.

    Al-rich YxAl1-xN thin films were synthesized and reported for the first time. Formation of solid solution was observed up to x=0.22 and an increase in growth temperature up to 900°C improved the crystalline quality of the YxAl1-xN films. The band gap of YxAl1-xN decreased from 6.2 eV for AlN down to 4.5 eV (x=0.22) and was shown to follow Vegard’s rule. Refractive indices and extinction coefficients were also determined. Lattice constants of wurtzite YxAl1-xN measured experimentally are in good agreement with theoretical predictions obtained through ab initio calculations. The mixing enthalpy

    Delarbeid
    1. Increased electromechanical coupling in w-ScxAl1-xN
    Åpne denne publikasjonen i ny fane eller vindu >>Increased electromechanical coupling in w-ScxAl1-xN
    Vise andre…
    2010 (engelsk)Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 97, nr 11, s. 112902-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    AlN is challenged as the material choice in important thin film electroacoustic devices for modern wireless communication applications. We present the promise of superior electromechanical coupling (kt2), in w−ScxAl1−xN by studying its dielectric properties. w−ScxAl1−xN (0≤x≤0.3) thin films grown by dual reactive magnetron sputtering exhibited low dielectric losses along with minor increased dielectric constant (ε). Ellipsometry measurements of the high frequency ε showed good agreement with density function perturbation calculations. Our data show that kt2 will improve from 7% to 10% by alloying AlN with up to 20 mol % ScN.

     

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-59839 (URN)10.1063/1.3489939 (DOI)000282032900055 ()
    Merknad
    Original Publication: Gunilla Wingqvist, Ferenc Tasnadi, Agne Zukauskaite, Jens Birch, Hans Arwin and Lars Hultman, Increased electromechanical coupling in w-ScxAl1-xN, 2010, Applied Physics Letters, (97), 11, 112902. http://dx.doi.org/10.1063/1.3489939 Copyright: American Institute of Physics http://www.aip.org/ Tilgjengelig fra: 2010-09-27 Laget: 2010-09-27 Sist oppdatert: 2021-12-29bibliografisk kontrollert
    2. Microstructure and Dielectric Properties of Piezoelectric Magnetron Sputtered w-ScxAl1-xN thin films
    Åpne denne publikasjonen i ny fane eller vindu >>Microstructure and Dielectric Properties of Piezoelectric Magnetron Sputtered w-ScxAl1-xN thin films
    Vise andre…
    2012 (engelsk)Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, nr 9, s. 093527-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Piezoelectric wurtzite ScxAl1-xN (x=0, 0.1, 0.2, 0.3) thin films were epitaxially grown by reactive magnetron co-sputtering from elemental Sc and Al targets. Al2O3(0001) wafers with TiN(111) seed and electrode layers were used as substrates. X-ray diffraction shows that an increase in the Sc content results in the degradation of the crystalline quality. Samples grown at 400 °C possess true dielectric behavior with quite low dielectric losses and the leakage current is negligible. For ScAlN samples grown at 800 °C, the crystal structure is poor and leakage current is high. Transmission electron microscopy with energy dispersive x-ray spectroscopy mapping shows a mass separation into ScN-rich and AlN-rich domains for x≥0.2 when substrate temperature is increased from 400 to 800 °C. The piezoelectric response of epitaxial ScxAl1-xN films measured by piezoresponse force microscopy and double beam interferometry shows up to 180% increase by the addition of Sc up to x=0.2 independent of substrate temperature, in good agreement with previous theoretical predictions based on density-functional theory.

    sted, utgiver, år, opplag, sider
    American Institute of Physics (AIP), 2012
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-76471 (URN)10.1063/1.4714220 (DOI)000304109900044 ()
    Tilgjengelig fra: 2012-04-10 Laget: 2012-04-10 Sist oppdatert: 2021-12-29bibliografisk kontrollert
    3. Nanoprobe Mechanical and Piezoelectric Characterization of ScxAl1-xN(0001) Thin Films
    Åpne denne publikasjonen i ny fane eller vindu >>Nanoprobe Mechanical and Piezoelectric Characterization of ScxAl1-xN(0001) Thin Films
    Vise andre…
    2015 (engelsk)Inngår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, nr 3, s. 666-673Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Nanoindentation with in-situ electrical characterization was used to characterize piezoelectric scandium aluminum nitride (ScxAl1-xN) thin films with Sc contents up to x=0.3. The films were prepared by reactive magnetron sputtering using Al2O3 substrates with TiN seed layer/bottom electrodes at a substrate temperature of 400 °C. X-ray diffraction shows c-axis oriented wurtzite ScxAl1-xN, where the crystal quality decreases with increasing x. Piezoresponse force microscopy in mapping mode shows a single piezoelectric polarization phase in all samples. The hardness and decreases from 17 GPa in AlN to 11 GPa in Sc0.3Al0.7N, while reduced elastic modulus decreases from 265 GPa to 224 GPa, respectively. Both direct and converse piezoelectric measurements are demonstrated by first applying the load and generating the voltage and later by applying the voltage and measuring film displacement using a conductive boron doped nanoindenter tip. The Sc0.2Al0.8N films exhibit an increase in generated voltage by 15% in comparison to AlN and a correspondingly larger displacement upon applied voltage, comparable to results obtained by double beam interferometry and piezoresponse force microscopy.

     

    sted, utgiver, år, opplag, sider
    John Wiley & Sons, 2015
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-103830 (URN)10.1002/pssa.201431634 (DOI)000351530800029 ()
    Merknad

    On the day of the defence date of the Ph.D. Thesis, the status of this article was Manuscript.

    Tilgjengelig fra: 2014-01-29 Laget: 2014-01-29 Sist oppdatert: 2021-12-29bibliografisk kontrollert
    4. Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices
    Åpne denne publikasjonen i ny fane eller vindu >>Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices
    Vise andre…
    2015 (engelsk)Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 94, s. 101-110Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Pseudomorphic stabilization in wurtzite ScxAl1-xN/AlN and ScxAl1-xN/InyAl1-yN superlattices (x=0.2, 0.3, and 0.4; y=0.2-0.72), grown by reactive magnetron sputter epitaxy was investigated. X-ray diffraction and transmission electron microscopy show that in ScxAl1-xN/AlN superlattices the compressive biaxial stresses due to positive lattice mismatch in Sc0.3Al0.7N and Sc0.4Al0.6N lead to loss of epitaxy, although the structure remains layered. For the negative lattice mismatched In-rich ScxAl1-xN/InyAl1-yN superlattices a tensile biaxial stress promotes the stabilization of wurtzite ScxAl1-xN even for the highest investigated concentration x=0.4. Ab initio calculations with fixed in-plane lattice parameters show a reduction in mixing energy for wurtzite ScxAl1-xN under tensile stress when x≥0.375 and support the experimental results.

    sted, utgiver, år, opplag, sider
    Elsevier, 2015
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-103831 (URN)10.1016/j.actamat.2015.04.033 (DOI)000357143500010 ()
    Tilgjengelig fra: 2014-01-29 Laget: 2014-01-29 Sist oppdatert: 2021-12-29bibliografisk kontrollert
    5. YxAl1-xN Thin Films
    Åpne denne publikasjonen i ny fane eller vindu >>YxAl1-xN Thin Films
    Vise andre…
    2012 (engelsk)Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, nr 42, s. 422001-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Reactive magnetron sputtering was used to deposit YxAl1-xN thin films, 0≤x≤0.22, onto Al2O3(0001) and Si(100) substrates. X-ray diffraction and analytical electron microscopy show that the films are solid solutions. Lattice constants are increasing with Y concentration, in agreement with ab initio calculations. Spectroscopic ellipsometry measurements reveal a band gap decrease from 6.2 eV (x=0) down to 4.9 eV (x=0.22). Theoretical investigations within the special quasirandom structure approach show that the wurtzite structure has the lowest mixingenthalpy for 0≤x≤0.75.

    sted, utgiver, år, opplag, sider
    Institute of Physics Publishing (IOPP), 2012
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-76472 (URN)10.1088/0022-3727/45/42/422001 (DOI)000309766700001 ()
    Merknad

    funding agencies|Linkoping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM)||Swedish Research Council (VR)|349-2008-6582|FCT Portugal|SFRH/BPD/66818/2009|VR|2010-3848|Swedish Governmental Agency for Innovation Systems (VINNOVA)|2011-03486|

    Tilgjengelig fra: 2012-04-10 Laget: 2012-04-10 Sist oppdatert: 2023-12-28bibliografisk kontrollert
    6. Bandgap Engineering and Optical Constants of YxAl1-xN Alloys
    Åpne denne publikasjonen i ny fane eller vindu >>Bandgap Engineering and Optical Constants of YxAl1-xN Alloys
    Vise andre…
    2013 (engelsk)Inngår i: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 52, nr 8Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We study wurtzite Yx Al1-xN (0 andlt;= x andlt;= 0:22) films with (0001) orientation deposited by magnetron sputtering epitaxy on Si(100) substrates and we determine the alloys band gap energies and optical constants. Room temperature spectroscopic ellipsometry (SE) is employed in the energy range from 1 to 6.3 eV, and data modeling based on the standard dielectric function model is used. As a result of the SE data analysis the Yx Al1-xN refractive index and extinction coefficient are determined. The band gap of Yx Al1-xN is found to decrease linearly from 6.2 eV (x=0) down to 4.5 eV (x=0:22). We further observe an increase of the refractive index with increasing Y content; from 1.93 to 2.20 (at 2 eV) for x=0 and 0.22, respectively, reflecting the increase in material density.

    sted, utgiver, år, opplag, sider
    Japan Society of Applied Physics, 2013
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-98153 (URN)10.7567/JJAP.52.08JM02 (DOI)000323883100159 ()
    Merknad

    Funding Agencies|FCT|REF:SFRH/BPD/66818/2009|Swedish Research Council (VR)|2010-3848|Linko "ping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM)||Swedish Governmental Agency for Innovation Systems (VINNOVA)|2011-03486|

    Tilgjengelig fra: 2013-09-30 Laget: 2013-09-30 Sist oppdatert: 2023-12-28
    Fulltekst (pdf)
    Metastable ScAlN and YAlN Thin Films Grown by Reactive Magnetron Sputter Epitaxy
    Download (pdf)
    omslag
  • 29467. Bestill onlineKjøp publikasjonen >>
    Žukauskaitė, Agnė
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Metastable YAlN and ScAlN thin films: growth and characterization2012Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    ScxAl1-xN and YxAl1-xN thin films were deposited in a ultra high vacuum system using reactive magnetron co-sputtering from elemental Al, Sc and Y targets in Ar/N2. Their mechanical, electrical, optical, and piezoelectrical properties were investigated with the help of transmission electron microscopy, xray diffraction, ellipsometry, I-V and C-V measurements, and two different techniques for piezoelectric characterization: piezoresponse force microscopy and double beam interferometry. Compared to AlN, improved electromechanical coupling and increase in piezoelectric response was found in ScxAl1-xN/TiN/Al2O3 structures with Sc content up to x=0.2. Microstructure of the films had a stronger influence on piezoelectric properties than the crystalline quality, which affected the leakage currents. YxAl1-xN thin films show a formation of solid solution up to x=0.22. Lattice constants obtained experimentally are in good agreement with theoretical predictions obtained through first principle (ab initio) calculations using density-functional formalism. The mixing enthalpy for wurtzite, cubic, and layered hexagonal phases of the YxAl1-xN system was also calculated.

    Delarbeid
    1. Increased electromechanical coupling in w-ScxAl1-xN
    Åpne denne publikasjonen i ny fane eller vindu >>Increased electromechanical coupling in w-ScxAl1-xN
    Vise andre…
    2010 (engelsk)Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 97, nr 11, s. 112902-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    AlN is challenged as the material choice in important thin film electroacoustic devices for modern wireless communication applications. We present the promise of superior electromechanical coupling (kt2), in w−ScxAl1−xN by studying its dielectric properties. w−ScxAl1−xN (0≤x≤0.3) thin films grown by dual reactive magnetron sputtering exhibited low dielectric losses along with minor increased dielectric constant (ε). Ellipsometry measurements of the high frequency ε showed good agreement with density function perturbation calculations. Our data show that kt2 will improve from 7% to 10% by alloying AlN with up to 20 mol % ScN.

     

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-59839 (URN)10.1063/1.3489939 (DOI)000282032900055 ()
    Merknad
    Original Publication: Gunilla Wingqvist, Ferenc Tasnadi, Agne Zukauskaite, Jens Birch, Hans Arwin and Lars Hultman, Increased electromechanical coupling in w-ScxAl1-xN, 2010, Applied Physics Letters, (97), 11, 112902. http://dx.doi.org/10.1063/1.3489939 Copyright: American Institute of Physics http://www.aip.org/ Tilgjengelig fra: 2010-09-27 Laget: 2010-09-27 Sist oppdatert: 2021-12-29bibliografisk kontrollert
    2. Microstructure and Dielectric Properties of Piezoelectric Magnetron Sputtered w-ScxAl1-xN thin films
    Åpne denne publikasjonen i ny fane eller vindu >>Microstructure and Dielectric Properties of Piezoelectric Magnetron Sputtered w-ScxAl1-xN thin films
    Vise andre…
    2012 (engelsk)Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, nr 9, s. 093527-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Piezoelectric wurtzite ScxAl1-xN (x=0, 0.1, 0.2, 0.3) thin films were epitaxially grown by reactive magnetron co-sputtering from elemental Sc and Al targets. Al2O3(0001) wafers with TiN(111) seed and electrode layers were used as substrates. X-ray diffraction shows that an increase in the Sc content results in the degradation of the crystalline quality. Samples grown at 400 °C possess true dielectric behavior with quite low dielectric losses and the leakage current is negligible. For ScAlN samples grown at 800 °C, the crystal structure is poor and leakage current is high. Transmission electron microscopy with energy dispersive x-ray spectroscopy mapping shows a mass separation into ScN-rich and AlN-rich domains for x≥0.2 when substrate temperature is increased from 400 to 800 °C. The piezoelectric response of epitaxial ScxAl1-xN films measured by piezoresponse force microscopy and double beam interferometry shows up to 180% increase by the addition of Sc up to x=0.2 independent of substrate temperature, in good agreement with previous theoretical predictions based on density-functional theory.

    sted, utgiver, år, opplag, sider
    American Institute of Physics (AIP), 2012
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-76471 (URN)10.1063/1.4714220 (DOI)000304109900044 ()
    Tilgjengelig fra: 2012-04-10 Laget: 2012-04-10 Sist oppdatert: 2021-12-29bibliografisk kontrollert
    3. YxAl1-xN Thin Films
    Åpne denne publikasjonen i ny fane eller vindu >>YxAl1-xN Thin Films
    Vise andre…
    2012 (engelsk)Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, nr 42, s. 422001-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Reactive magnetron sputtering was used to deposit YxAl1-xN thin films, 0≤x≤0.22, onto Al2O3(0001) and Si(100) substrates. X-ray diffraction and analytical electron microscopy show that the films are solid solutions. Lattice constants are increasing with Y concentration, in agreement with ab initio calculations. Spectroscopic ellipsometry measurements reveal a band gap decrease from 6.2 eV (x=0) down to 4.9 eV (x=0.22). Theoretical investigations within the special quasirandom structure approach show that the wurtzite structure has the lowest mixingenthalpy for 0≤x≤0.75.

    sted, utgiver, år, opplag, sider
    Institute of Physics Publishing (IOPP), 2012
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-76472 (URN)10.1088/0022-3727/45/42/422001 (DOI)000309766700001 ()
    Merknad

    funding agencies|Linkoping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM)||Swedish Research Council (VR)|349-2008-6582|FCT Portugal|SFRH/BPD/66818/2009|VR|2010-3848|Swedish Governmental Agency for Innovation Systems (VINNOVA)|2011-03486|

    Tilgjengelig fra: 2012-04-10 Laget: 2012-04-10 Sist oppdatert: 2023-12-28bibliografisk kontrollert
    Fulltekst (pdf)
    Metastable YAlN and ScAlN thin films: growth and characterization
    Download (pdf)
    omslag
  • 29468.
    Žukauskaitė, Agnė
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Tholander, Christopher
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pališaitis, Justinas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Persson, Per O. Å.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Ben Sedrine, Nebiha
    Instituto Tecnológico e Nuclear, 2686-953 Sacavém and CFNUL, Lisbon 1649-003, Portugal.
    Tasnádi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    YxAl1-xN Thin Films2012Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, nr 42, s. 422001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reactive magnetron sputtering was used to deposit YxAl1-xN thin films, 0≤x≤0.22, onto Al2O3(0001) and Si(100) substrates. X-ray diffraction and analytical electron microscopy show that the films are solid solutions. Lattice constants are increasing with Y concentration, in agreement with ab initio calculations. Spectroscopic ellipsometry measurements reveal a band gap decrease from 6.2 eV (x=0) down to 4.9 eV (x=0.22). Theoretical investigations within the special quasirandom structure approach show that the wurtzite structure has the lowest mixingenthalpy for 0≤x≤0.75.

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    fulltext
  • 29469.
    Žukauskaitė, Agnė
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. Fraunhofer Institute for Applied Solid State Physics, Freiburg, Germany.
    Tholander, Christopher
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Tasnádi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pališaitis, Justinas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Persson, Per O. Å.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices2015Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 94, s. 101-110Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pseudomorphic stabilization in wurtzite ScxAl1-xN/AlN and ScxAl1-xN/InyAl1-yN superlattices (x=0.2, 0.3, and 0.4; y=0.2-0.72), grown by reactive magnetron sputter epitaxy was investigated. X-ray diffraction and transmission electron microscopy show that in ScxAl1-xN/AlN superlattices the compressive biaxial stresses due to positive lattice mismatch in Sc0.3Al0.7N and Sc0.4Al0.6N lead to loss of epitaxy, although the structure remains layered. For the negative lattice mismatched In-rich ScxAl1-xN/InyAl1-yN superlattices a tensile biaxial stress promotes the stabilization of wurtzite ScxAl1-xN even for the highest investigated concentration x=0.4. Ab initio calculations with fixed in-plane lattice parameters show a reduction in mixing energy for wurtzite ScxAl1-xN under tensile stress when x≥0.375 and support the experimental results.

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    fulltext
  • 29470.
    Žukauskaitė, Agnė
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Wingqvist, Gunilla
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pališaitis, Justinas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Jensen, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Persson, Per O. Å.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Matloub, Ramin
    Ceramics Laboratory, Ecole Polytechnique Fédérale de Lausanne EPFL, Lausanne, SwitzerlandNational Laboratory, Oak Ridge, TN 37831, United States.
    Muralt, Paul
    Ceramics Laboratory, Ecole Polytechnique Fédérale de Lausanne EPFL, Lausanne, Switzerland.
    Kim, Yunseok
    Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Microstructure and Dielectric Properties of Piezoelectric Magnetron Sputtered w-ScxAl1-xN thin films2012Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, nr 9, s. 093527-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Piezoelectric wurtzite ScxAl1-xN (x=0, 0.1, 0.2, 0.3) thin films were epitaxially grown by reactive magnetron co-sputtering from elemental Sc and Al targets. Al2O3(0001) wafers with TiN(111) seed and electrode layers were used as substrates. X-ray diffraction shows that an increase in the Sc content results in the degradation of the crystalline quality. Samples grown at 400 °C possess true dielectric behavior with quite low dielectric losses and the leakage current is negligible. For ScAlN samples grown at 800 °C, the crystal structure is poor and leakage current is high. Transmission electron microscopy with energy dispersive x-ray spectroscopy mapping shows a mass separation into ScN-rich and AlN-rich domains for x≥0.2 when substrate temperature is increased from 400 to 800 °C. The piezoelectric response of epitaxial ScxAl1-xN films measured by piezoresponse force microscopy and double beam interferometry shows up to 180% increase by the addition of Sc up to x=0.2 independent of substrate temperature, in good agreement with previous theoretical predictions based on density-functional theory.

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587588589590 29451 - 29470 of 29470
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