Search

Search Results

• 1. [Article] Interpreting Activation Energies in Digital Image Sensors

  We present a study demonstrating the dependence of apparent activation energies on signal charge in digital image sensors. The data presented in this paper are for a charge-coupled device imager, but the ...

  Citation × Citation Citation Abstract Copy Title: Interpreting Activation Energies in Digital Image Sensors Author: Dunlap, Justin C., Blouke, Morley M., Bodegom, Erik, Widenhorn, Ralf Year: 2015 We present a study demonstrating the dependence of apparent activation energies on signal charge in digital image sensors. The data presented in this paper are for a charge-coupled device imager, but the analysis can be applied to CMOS sensors or generally to any system that shows nonlinearity with respect to time. Activation energies for some pixels are observed to vary between values at about half the bandgap of silicon, when calculated at low signal-charge levels, to values approaching the bandgap when calculated at high signal-charge levels. As such, the traditional method of calculating activation energies using a single exposure time at varying temperatures will result in different activation energies dependent on the exposure time chosen, making it difficult to draw physically meaningful conclusions from its value. Therefore, a method of calculating activation energies using a single signal-charge level is proposed, making it easier to correlate activation energies with impurities. Further, we demonstrate how a model of a pixel with a fixed location impurity in conjunction with a moving depletion edge, due to a changing depletion region size, can lead to this behavior. Title: Interpreting Activation Energies in Digital Image Sensors Author: Dunlap, Justin C., Blouke, Morley M., Bodegom, Erik, Widenhorn, Ralf Year: 2015 We present a study demonstrating the dependence of apparent activation energies on signal charge in digital image sensors. The data presented in this paper are for a charge-coupled device imager, but the analysis can be applied to CMOS sensors or generally to any system that shows nonlinearity with respect to time. Activation energies for some pixels are observed to vary between values at about half the bandgap of silicon, when calculated at low signal-charge levels, to values approaching the bandgap when calculated at high signal-charge levels. As such, the traditional method of calculating activation energies using a single exposure time at varying temperatures will result in different activation energies dependent on the exposure time chosen, making it difficult to draw physically meaningful conclusions from its value. Therefore, a method of calculating activation energies using a single signal-charge level is proposed, making it easier to correlate activation energies with impurities. Further, we demonstrate how a model of a pixel with a fixed location impurity in conjunction with a moving depletion edge, due to a changing depletion region size, can lead to this behavior. Close

• 2. [Article] High-Quality Chemical Vapor Deposition Graphene-Based Spin Transport Channels

  Spintronics reaches beyond typical charge-based information storage technologies by utilizing an addressable degree of freedom for electron manipulation, the electron spin polarization. With mounting experimental ...

  Citation × Citation Citation Abstract Copy Title: High-Quality Chemical Vapor Deposition Graphene-Based Spin Transport Channels Author: Lampert, Lester Florian Year: 2017 Spintronics reaches beyond typical charge-based information storage technologies by utilizing an addressable degree of freedom for electron manipulation, the electron spin polarization. With mounting experimental data and improved theoretical understanding of spin manipulation, spintronics has become a potential alternative to charge-based technologies. However, for a long time, spintronics was not thought to be feasible without the ability to electrostatically control spin conductance at room temperature. Only recently, graphene, a 2D honeycomb crystalline allotrope of carbon only one atom thick, was identified because of its predicted, long spin coherence length and experimentally realized electrostatic gate tunability. However, there exist several challenges with graphene spintronics implementation including weak spin-orbit coupling that provides excellent spin transfer yet prevents charge to spin current conversion, and a conductivity mismatch due to the large difference in carrier density between graphene and a ferromagnet (FM) that must be mitigated by use of a tunnel barrier contact. Additionally, the usage of graphene produced via CVD methods amenable to semiconductor industry in conjunction with graphene spin valve fabrication must be explored in order to promote implementation of graphene-based spintronics. Despite advances in the area of graphene-based spintronics, there is a lack of understanding regarding the coupling of industry-amenable techniques for both graphene synthesis and lateral spin valve fabrication. In order to make any impact on the application of graphene spintronics in industry, it is critical to demonstrate wafer-scale graphene spin devices enabled by wafer-scale graphene synthesis, which utilizes thin film, wafer-supported CVD growth methods. In this work, high-quality graphene was synthesized using a vertical cold-wall furnace and catalyst confinement on both SiO2/Si and C-plane sapphire wafers and the implementation of the as-grown graphene for fabrication of graphene-based non-local spin valves was examined. Optimized CVD graphene was demostrated to have ID/G ≈ 0.04 and I2D/G ≈ 2.3 across a 2" diameter graphene film with excellent continuity and uniformity. Since high-quality, large-area, and continuous CVD graphene was grown, it enabled the fabrication of large device arrays with 40 individually addressable non-local spin valves exhibiting 83% yield. Using these arrays, the effects of channel width and length, ferromagnetic-tunnel barrier width, tunnel barrier thickness, and level of oxidation for Ti-based tunnel barrier contacts were elucidated. Non-local, in-plane magnetic sweeps resulted in high signal-to-noise ratios with measured [Delta]RNL across the as-fabricated arrays as high as 12 Ω with channel lengths up to 2 µm. In addition to in-plane magnetic field spin signal values, vertical magnetic field precession Hanle effect measurements were conducted. From this, spin transport properties were extracted including: spin polarization efficiency, coherence lifetime, and coherence distance. The evaluation of industry-amenable production methods of both high-quality graphene and lateral graphene non-local spin valves are the first steps toward promoting the feasibility of graphene as a lateral spin transport interconnect material in future spintronics applications. By addressing issues using a holistic approach, from graphene synthesis to spin transport implementation, it is possible to begin assessment of the challenges involved for graphene spintronics. Title: High-Quality Chemical Vapor Deposition Graphene-Based Spin Transport Channels Author: Lampert, Lester Florian Year: 2017 Spintronics reaches beyond typical charge-based information storage technologies by utilizing an addressable degree of freedom for electron manipulation, the electron spin polarization. With mounting experimental data and improved theoretical understanding of spin manipulation, spintronics has become a potential alternative to charge-based technologies. However, for a long time, spintronics was not thought to be feasible without the ability to electrostatically control spin conductance at room temperature. Only recently, graphene, a 2D honeycomb crystalline allotrope of carbon only one atom thick, was identified because of its predicted, long spin coherence length and experimentally realized electrostatic gate tunability. However, there exist several challenges with graphene spintronics implementation including weak spin-orbit coupling that provides excellent spin transfer yet prevents charge to spin current conversion, and a conductivity mismatch due to the large difference in carrier density between graphene and a ferromagnet (FM) that must be mitigated by use of a tunnel barrier contact. Additionally, the usage of graphene produced via CVD methods amenable to semiconductor industry in conjunction with graphene spin valve fabrication must be explored in order to promote implementation of graphene-based spintronics. Despite advances in the area of graphene-based spintronics, there is a lack of understanding regarding the coupling of industry-amenable techniques for both graphene synthesis and lateral spin valve fabrication. In order to make any impact on the application of graphene spintronics in industry, it is critical to demonstrate wafer-scale graphene spin devices enabled by wafer-scale graphene synthesis, which utilizes thin film, wafer-supported CVD growth methods. In this work, high-quality graphene was synthesized using a vertical cold-wall furnace and catalyst confinement on both SiO2/Si and C-plane sapphire wafers and the implementation of the as-grown graphene for fabrication of graphene-based non-local spin valves was examined. Optimized CVD graphene was demostrated to have ID/G ≈ 0.04 and I2D/G ≈ 2.3 across a 2" diameter graphene film with excellent continuity and uniformity. Since high-quality, large-area, and continuous CVD graphene was grown, it enabled the fabrication of large device arrays with 40 individually addressable non-local spin valves exhibiting 83% yield. Using these arrays, the effects of channel width and length, ferromagnetic-tunnel barrier width, tunnel barrier thickness, and level of oxidation for Ti-based tunnel barrier contacts were elucidated. Non-local, in-plane magnetic sweeps resulted in high signal-to-noise ratios with measured [Delta]RNL across the as-fabricated arrays as high as 12 Ω with channel lengths up to 2 µm. In addition to in-plane magnetic field spin signal values, vertical magnetic field precession Hanle effect measurements were conducted. From this, spin transport properties were extracted including: spin polarization efficiency, coherence lifetime, and coherence distance. The evaluation of industry-amenable production methods of both high-quality graphene and lateral graphene non-local spin valves are the first steps toward promoting the feasibility of graphene as a lateral spin transport interconnect material in future spintronics applications. By addressing issues using a holistic approach, from graphene synthesis to spin transport implementation, it is possible to begin assessment of the challenges involved for graphene spintronics. Close