| 31. |
- Liu, Q., et al.
(författare)
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High responsivity sensing of unfocused laser and white light using graphene photodetectors grown by chemical vapor deposition
- 2016
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Ingår i: Optical Materials Express. - 2159-3930. ; 6:7, s. 2158-2164
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Tidskriftsartikel (refereegranskat)abstract
- Graphene photodetectors grown by chemical vapor deposition are fabricated for unfocused laser and white light sensing. The unfocused light enlarges the illuminated graphene area and mimics the real-life sensing conditions, yielding a responsivity of 104 mA/W at room temperature without enhancing absorbance by waveguide and plasmonics. The devices are based on positive photoconductivity from the electron-hole photocarrier pairs and the bolometric-effect-induced negative photoconductivity. The buried off-center local gate induces a net internal potential in the graphene. The relative strength of the two photoconductivities depends on the gate voltage. The technology is scalable, which is a step ahead toward real applications.
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| 32. |
- Lockhart de la Rosa, César Javier, 1987, et al.
(författare)
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Frame assisted H2O electrolysis induced H2 bubbling transfer of large area graphene grown by chemical vapor deposition on Cu
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:2
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Tidskriftsartikel (refereegranskat)abstract
- An improved technique for transferring large area graphene grown by chemical vapor deposition on copper is presented. It is based on mechanical separation of the graphene/copper by H-2 bubbles during H2O electrolysis, which only takes a few tens of seconds while leaving the copper cathode intact. A semi-rigid plastic frame in combination with thin polymer layer span on graphene gives a convenient way of handling-and avoiding wrinkles and holes in graphene. Optical and electrical characterizations prove the graphene quality is better than that obtained by traditional wet etching transfer. This technique appears to be highly reproducible and cost efficient.
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| 33. |
- Lu, Yu, et al.
(författare)
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Electroless deposition of high-uniformity nickel microbumps with ultrahigh resolution of 8 μm pitch for monolithic Micro-LED display
- 2024
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Ingår i: Materials Science in Semiconductor Processing. - 1369-8001. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- Micro-light-emitting diode (Micro-LED) displays have attracted growing attention due to their unsurpassed properties that satisfy the requirements of reality/virtual reality (AR/VR) displays. A crucial procedure of monolithic integration technology in high-density microdisplays is the interconnection process, which is intimately associated with the quality of the display device. Microfluidic electroless interconnection (MELI), an innovative low-temperature and pressure-free chip-stacking approach that eliminates the warpage-induced issues and cracking damage of the chip caused by thermo-compression bonding (TCB), holds great promise as a technology for establishing interconnections between the CMOS driver and Micro-LED. However, the requirement for the consistency of the microbump arrays and the risk of creating bridges is significantly intensified with smaller gaps in stacked chips, which restricts the application range of MELI to high-density interconnects. This paper analyzes the feasibility of further lowering the stand-off height of stacked chips in ultrafine pitch interconnects by optimizing the bump preparation process. The plasma modification time and surfactant concentration during the bump preparation process have been investigated. The result indicated that microbump arrays with a uniformity of less than 3% could be successfully manufactured by employing a 7-min plasma treatment and incorporating optimal surfactants, which catalyzes the implementation of the subsequent vertical interconnection process and eventually enhances yields of Micro-LEDs.
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| 34. |
- Lu, Yu, et al.
(författare)
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Electroless deposition of nickel microbumps for fine-pith flip-chip bonding
- 2024
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Ingår i: Journal of Physics: Conference Series. - 1742-6588 .- 1742-6596. ; 2783:1
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Konferensbidrag (refereegranskat)abstract
- The reliability of micro-light-emitting diode (Micro-LED) is closely associated with the uniformity of microbumps arrays. With continual decreases in pixel pitch in recent years, it is a challenge to guarantee the uniformity of bump arrays. To satisfy current requirements for ultra-high-density interconnections, this study proposes an electroless plating method for fabricating highly uniform nickel microbumps. This technique differs from electroplating, in which the morphology and consistency of microbumps can be easily controlled. Furthermore, it is a high-selectivity and cost-effective method of microbumps fabrication that eliminates solder wastage and avoids metal lift-off in traditional evaporation. To minimize the non-uniformity of the bumps, we aim to optimize the oxygen plasma treatment parameters and deposition intervals to eliminate the issues of skip plating, hydrogen bubble entrapment, and nodules. Under the combined effect of plasma treatment and intermittent deposition method, microbump arrays with less than 5% uniformity were successfully prepared, achieving the demands of high-density bonding. In addition, the preparation process is highly reproducible, extending the application range of this technique.
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| 35. |
- Nam, Youngwoo, 1983, et al.
(författare)
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Graphene p-n-p junctions controlled by local gates made of naturally oxidized thin aluminium films
- 2012
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 50:5, s. 1987-1992
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Tidskriftsartikel (refereegranskat)abstract
- Graphene structures with both top- and bottom-electrostatic gates are studied. The top gate is made of thin aluminium (Al) film deposited directly onto graphene, with no prior dielectric layer in between. Natural oxidation of Al at the interface with graphene results in an insulating barrier proving useful in making top gates to graphene. For electrically disconnected top gate, graphene resistance as a function of the slowly-varying back-gate voltage shows hysteresis which reveals dielectric properties of the barrier. The estimated barrier thickness is only 2 nm allowing for very sharp profiles of the electric field in graphene devices. By applying voltages to both back- and top gates, effective p–n–p junctions with sharp interfaces can be created.
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| 36. |
- Nam, Youngwoo, 1983, et al.
(författare)
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Quantum Hall effect in graphene decorated with disordered multilayer patches
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:233, s. 233110-
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Tidskriftsartikel (refereegranskat)abstract
- Quantum Hall effect (QHE) is observed in graphene grown by chemical vapour deposition using platinum catalyst. The QHE is even seen in samples which are irregularly decorated with disordered multilayer graphene patches and have very low mobility (
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| 37. |
- Nam, Youngwoo, 1983, et al.
(författare)
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Unusual thermopower of inhomogeneous graphene grown by chemical vapor deposition
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:2, s. 021902 -
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Tidskriftsartikel (refereegranskat)abstract
- We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone.
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| 38. |
- Nie, Junyang, et al.
(författare)
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Systematic study on size and temporal dependence of micro-LED arrays for display applications
- 2023
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Ingår i: Photonics Research. - 2327-9125. ; 11:4, s. 549-557
-
Tidskriftsartikel (refereegranskat)abstract
- Micro-LEDs are one of the most promising candidates for next-generation displays, yet they are inconvenienced by the efficiency reduction induced by the sidewall defects when pursuing further scaled-down device dimensions. We have systematically investigated both the size and temporal dependence of micro-LEDs. Micro-LED arrays with a mesa size ranging from 7 to 100 μm were prepared for display purposes. The luminance and external quantum efficiency (EQE) were measured and discussed. Surprisingly, micro-LED arrays with a smaller mesa size exhibit a higher EQE under 100 ns pulse duration operation when compared with longer pulse duration operations. Under certain short-pulsed excitation, a 7 × 7 μm2 micro-LED array even exhibits a >20% higher EQE as compared to the direct current (DC) or the long duration pulse operation condition.We thus concluded that the notorious efficiency reduction induced by sidewall defects in small-sized micro-LED arrays could be significantly reduced by applying short-pulse voltages.
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| 39. |
- Pan, G. Z., et al.
(författare)
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Analysis of optical coupling behavior in two-dimensional implant-defined coherently coupled vertical-cavity surface-emitting laser arrays
- 2018
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Ingår i: Photonics Research. - 2327-9125. ; 6:11, s. 1048-1055
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Tidskriftsartikel (refereegranskat)abstract
- Optical coupling behavior and associated effects in two-dimensional implant-defined coherently coupled vertical-cavity surface-emitting laser (VCSEL) arrays are studied via both experiments and theoretical calculations. Experiments show that optical coupling between array elements can enhance the array’s output power. Additionally, optical coupling via leaky optical fields can provide extra optical gain for the array elements, which can then reduce the thresholds of these elements. Elements can even be pumped without current injection to emit light by receiving a strong leaky optical field from other array elements. Optical coupling can also cause unusual phenomena: the central elements in large-area coherently coupled VCSEL arrays that lase prior to the outer elements when the arrays are biased, or the average injection current required for each element to lase, which is much lower than the threshold for a single VCSEL. Theoretical calculations are performed to explain the experimental results.
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| 40. |
- Pan, G. Z., et al.
(författare)
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Dependence of Beam Quality on Optical Intensity Asymmetry in In-Phase Coherently Coupled VCSEL Array
- 2018
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 54:3
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Tidskriftsartikel (refereegranskat)abstract
- Dependence of beam quality on optical intensity asymmetry among elements in in-phase coherently coupled vertical cavity surface emitting lasers array is analyzed using the finite-difference time domain solutions software. The analysis results reveal that the coupling efficiency of in-phased array decreases and the divergence increases as the level of optical intensity asymmetry increases. Furthermore, an addressable separated-contact three-element triangular in-phased array is fabricated and measured to verify the analysis. The array exhibits a relatively high of coupling efficiency of 24% and a near-diffraction-limit divergence of 3.2° (1.12 times of the diffraction limit, D.L.) when the optical intensity of each element is adjusted to be uniform. By degrading the optical intensity symmetry, the coupling efficiency decreases to 17.07% and the divergence increases to 4.03° ( 1.37× D.L.). After that, a much larger 10× 10 array exhibiting in-phase characteristics is produced and its beam quality and optical uniformity are measured and discussed. Analysis and experiment results demonstrate that symmetric optical intensity among elements is essential for in-phased array to achieve high beam quality. Employing separate contacts in the array is proved an effective way to obtain uniform optical intensity and achieve high beam quality.
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