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Liu Y.,Beijing Institute of Technology | Chen K.,Beijing NARI Smartchip Microelectronics Technology Company Ltd
Lecture Notes in Electrical Engineering | Year: 2015

In this paper, we proposed a new method to compress the CSI feedback. When the channel matrix is correlated, the DCT matrix works as a sparsifying basis to transform the channel matrix into a sparse form; the sparse signal is a feedback to the transmitter and reconstructed via the subspace pursuit (SP) recovery algorithm. Both theoretical analyses and simulation results show that the new method can introduce a huge computation cost reduction compared with the OMP algorithm and the codebook-based feedback scheme. © Springer International Publishing Switzerland 2015. Source

Shi D.,Beijing University of TechnologyBeijing | Feng S.,Beijing University of TechnologyBeijing | Zhang Y.,Beijing University of TechnologyBeijing | Qiao Y.,Beijing NARI Smartchip Microelectronics Technology Company Ltd | Deng B.,Beijing University of TechnologyBeijing
Microelectronics Journal | Year: 2015

Abstract In this paper, the superposition method is used to investigate the complete temperature field of a light-emitting diode (LED) packaging substrate, based on the results of transient temperature rise measurements and the thermal resistance coupling matrix. The feasibility of use of the superposition method in an LED array with multiple packages has been proved first by temperature comparisons with the simultaneous operation of an array (5×5) of 25 high power LEDs mounted on a metal core printed circuit board (MCPCB). Compared with existing approaches, the superposition method will measure the internal temperature of chip directly, accurately and nondestructively. According to the relatively accurate and reliable self-heating and coupling temperature rise data, optimization scheme of LED lamp with multiple packages is proposed. The results show that increasing the heat source separation distance and improving the thermal conductivity of thermal interface materials will reduce the temperature rise and thermal non-uniformity. © 2015 Elsevier Ltd. Source

Qiao Y.,Beijing University of Technology | Feng S.,Beijing University of Technology | Zhang G.,Beijing NARI Smartchip Microelectronics Technology Company Ltd | Xiong C.,CAS Institute of Semiconductors | And 2 more authors.
IEEE Transactions on Electron Devices | Year: 2014

Thermomechanical cycle failure was analyzed in 808-nm high-power AlGaAs/GaAs laser diode bars (LDBs) in detail. Two thermal stress cycle experiments were carried out in these devices with peak thermal stresses of 19.4 and 33 MPa. The threshold current increase demonstrated a square-root dependence on the cycle number, and a tail and split in lasing spectrum were observed. This result was attributed to nonradiative recombination increasing with cycle number due to the diffusion of defects that accompanies band-structure renormalization. Furthermore, from X-ray diffraction measurements we found that the epitaxial layer remains monocrystalline during thermal stress cycling. We calculated the out-of-plane strain and in-plane stress induced by plastic deformation in the epitaxial layer based on the interplanar spacing in the crystal. Our results suggest that thermomechanical strain and stress were induced by pulsed operation, which led to degradation of the high-power LDBs. © 2014 IEEE. Source

Shi D.,Beijing University of Technology | Feng S.,Beijing University of Technology | Qiao Y.,Beijing NARI Smartchip Microelectronics Technology Company Ltd | Wen P.,CAS Suzhou Institute of Nano Technology and Nano Bionics
Solid-State Electronics | Year: 2015

Blue GaN-based laser diodes (LDs) have been characterized by thermal infrared imaging and transient thermal technique to obtain temperature distributions along the optical resonant cavity under continuous-wave (CW) operation. The highest temperature occurred at the emitting facet and the second higher temperature occurred in the other reflecting facet under injection current I = 100 mA with platform temperature of 308.15 K. The results are attributed to the nonradiative recombination in the active region and the reabsorption of laser light inside the cavity. And due to the different of optical flow density, the highest temperature appears in emitting facet. Based on diode forward voltage with temperature, transient thermal technique is used to obtain the temperature distribution along the top-down direction of LDs by the structure function method. The thermal resistance from chip to case is 47.3 K/W. The chip's thermal resistance is the main contribution. © 2015 Elsevier Ltd. All rights reserved. Source

Gong X.,Beijing University of Technology | Feng S.,Beijing University of Technology | Yang H.,Hebei Semiconductor Research Institute | An Z.,Hebei Semiconductor Research Institute | Qiao Y.,Beijing NARI Smartchip Microelectronics Technology Company Ltd
IEEE Transactions on Device and Materials Reliability | Year: 2015

The facet coating of GaAs-based laser diodes (LDs) stressed by constant current was studied in detail using focused ion beam, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy techniques. Our analysis found that, for Si/Al 2O 3 facet coating, silicon near the active area exposed to high laser intensity becomes diffused, making it thicker than the Si layer outside the active area. Oxygen diffused into the Si layer and the Si layer got oxidized. Such change of facet-coating thickness and composition causes the facet reflectivity to fluctuate and carriers to recombine nonradioactively and eventually lead to catastrophic optical damage. We conclude that the performance of LDs could be improved by optimizing their facet coating. © 2001-2011 IEEE. Source

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