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- Yuan, Ying Kuo, et al.
(författare)
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Applications of graphene transistor optimized fabrication process in monolithic integrated driving gallium nitride micro-light-emitting diode
- 2021
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Ingår i: Wuli Xuebao/Acta Physica Sinica. - : Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences. - 1000-3290. ; 70:19
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Tidskriftsartikel (refereegranskat)abstract
- In the information display field, micro-light-emitting diodes (micro-LEDs) possess high potentials and they are expected to lead the direction of developing the next-generation new display technologies. Their display performances are superior to those produced by the currently prevailing liquid crystal and organic light-emitting diode based technologies. However, the micro-LED pixels and their driving circuits are often fabricated on different wafers, which implies that the so-called mass transfer seems to be inevitable, thus facing an obvious bottleneck. In this paper, the emerging graphene field effect transistors are used as the driving elements and integrated onto the GaN micro-LEDs, which is because the pixels and drivers are prepared directly on the same wafer, the technical problem of mass transfer is fundamentally bypassed. Furthermore, in traditional lithographic process, the ultraviolet photoresist directly contacts the graphene, which introduces severe carrier doping, thereby leading to deteriorated graphene transistor properties. This, not surprisingly, further translates into lower performances of the integrated devices. In the present work, proposed is a technique in which the polymethyl methacrylate (PMMA) thin films act as both the protection layers and the interlayers when optimizing the graphene field effect transistor processing. The PMMA layers are sandwiched between the graphene and the ultraviolet photoresist, which is a brand new device fabrication process. First, the new process is tested in discrete graphene field effect transistors. Compared with those devices that are processed without the PMMA protection thin films, the graphene devices fabricated with the new technology typically show their Dirac point at a gate voltage (Vg) deviation from Vg = 0, that is, 22 V lower than their counterparts. In addition, an increase in the carrier mobility of 32% is also observed. Finally, after applying the newly developed fabrication process to the pixel-and-driver integrated devices, it is found that their performances are improved significantly. With this new technique, the ultraviolet photoresist no longer directly contacts the sensitive graphene channel because of the PMMA protection. The doping effect and the performance dropping are dramatically reduced. The technique is facile and cheap, and it is also applicable to two-dimensional materials besides graphene, such as MoS2 and h-BN. It is hoped that it is of some value for device engineers working in this field.
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| 3. |
- Zhang, Huichun, et al.
(författare)
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Wind tunnel experiment and regression model for spray drift
- 2015
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Ingår i: Transactions of the Chinese Society of Agricultural Engineering. - Beijing, China : Chinese Society of Agricultural Engineering. - 1002-6819. ; 31:3, s. 94-100
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Tidskriftsartikel (refereegranskat)abstract
- With greater environmental awareness, the movement of pesticides within and off of a spray target area is acritical public concern. Ideally, all of the material applied should be deposited within the targeted swath on the intendedpest or plant. But realistically, a portion of the spray remains airborne and is carried downwind to non-target areas.Airborne spray leaving the targeted area reduces the applied dosage, and could cause damage to neighboring plant andwater source or other detrimental environmental impacts. To study the influences of nozzle type, spray mixture and windspeed on spray drift, experiments were conducted using a wind tunnel. Spray drift risk was assessed by adding a tracer tothe spray mixture and measuring the quantities of spray deposited downwind from the nozzle on horizontal polythenelines with 2 mm diameter perpendicular to the wind direction in a vertical and a horizontal array. At a distance of 2 mdownwind from the static nozzle, five collector lines (V1 to V5) were positioned one above the other at the spacing of0.1 m to provide an estimate of the spray still airborne through this vertical profile. An additional five sampling collectorstrings (H1 to H5) were placed in a horizontal array with one-meter horizontal spacing at 0.1 m height to determine thefallout volumes and gradients of the spray from 2 to 6 m downwind. A water-soluble fluorescent tracer was dissolvedinto tap water as the spray liquid, and after the experiments, the collecting lines were washed with deionized water tomeasure deposit and drift. The results indicated that deposits on sampling collector decreased with increased verticalelevation and horizontal distance. Average fallout and airborne deposit resulting from the different spray applicationswere shown in the paper. These figures showed the expected fallout and airborne profiles for all tested nozzle types andsizes. The highest fallout deposits were measured at a position closest to the nozzle (H1) with a systematic decrease withthe distance from the nozzle. The highest airborne deposits were found at the lowest sampling collector (V1) with asystematic decrease with increasing height above the wind tunnel floor. Airborne spray drift was affected by wind speed.At all sample positions, deposits on collectors were reduced at lower wind speed. Nozzle’s structure was also found toinfluence droplet’s size, so injector/pre-orifice nozzle produced coarser droplets and reduced spray drift. The amount ofspray recovered is based on the amount of active ingredient of spray mixture within each droplet rather than the totaldroplet volume. On that basis, a multiple non-linear model for statistical drift prediction including four independent,non-correlated variables (target distance, wind speed, nozzle type and chemical type) was established. The regressionmodel provided a drift evaluation approach, and it was important in the interpretation of wind tunnel data for differentnozzle types, chemical types and sampling methodologies.
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