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The influence of the total thickness (periods of AlN/GaN SLs) of AlN/GaN superlattices (SLs) buffer on the static electrical properties of AlGaN/GaN HFETs is study for the purpose of improving device's breakdown voltage (BV) and reducing its on-resistance (RON). It is found that for top-GaN layer with a constant thickness of lμm, a proper thickness of AlN/GaN SLs buffer (such as 2.5 μm with 100 period...
In this paper, the leakage path and breakdown behavior of GaN on silicon substrate were studied systematically. Three terminal breakdown voltage characteristics of the samples with various ohmic contacts spacing were evaluated. With increasing the spacing between the contacts, the breakdown voltage increased linearly first and then saturated. In order to clarify the breakdown behavior, leakage path...
A simple double-layer transmitarray element operating at 20 GHz is proposed. The element consists of only two layers of cross dipoles connected by vias through the substrate. By changing the dipole length and tuning the positions of vias, a phase range of 317° with magnitude loss mostly less than 1 dB is achieved. Under 30° oblique incidence, the phase variation of the element is mostly less than...
In this paper, a Ku-band high-gain transmitarray design using triple-layer perforated FR-4 dielectric material is presented. Square holes in a sub-wavelength dielectric element are utilized to control the effective material properties. Two matching layers are designed by simply changing the hole size. A phase coverage over 360° with low element loss is achieved. A transmitarray with a circular aperture...
A novel reconfigurable reflectarray element with an internal slotted patch of tunable height is proposed. The slotted patch is inserted between a fixed upper patch and the ground plane, whose height is mechanically controlled by an actuator to achieve phase reconfigurability. Based on the Phoenix element concept, the initial and final states of the proposed element are almost the same, except a slight...
A graphene-based single-pole double-throw (SPDT) switch is presented for mm-wave applications. The proposed SPDT switch is realized by mounting graphene layers on the slot of slotted substrate integrated waveguide (SSIW). Simulations show the designed switch achieves a frequency bandwidth from 59.5 GHz to 60.8 GHz with −3 dB insertion loss. A minimum insertion loss of −1.1 dB is obtained at 60 GHz,...
Aligned electrospun nanofibers have gained increasing interest due to unique electrical, optical, and mechanical properties. Several works have devoted to reshaping the electrospinning process through modifying the collector structures. However, more investigations are still required. Here, the influence of collector structures and some key electrospinning parameters on fiber alignment by using static...
In this paper, a new low-cost metal-only reflectarray antenna working at 12.5 GHz is proposed. It is made of only two pieces of metallic sheets separated by an air layer. The simulated aperture efficiency of a representative reflectarray antenna is 55.3%, which is comparable with conventional reflectarrays. By uniting isolated patches into a whole structure, the metal-only reflectarray does not need...
In this paper, a novel transmitarray is proposed for high-gain antennas at Ka-band. The element with two-layer structure is designed for simplicity compared with previous work. To improve the element's transmission performance, vias are added to connect two metallic layers through a single dielectric substrate. For the purpose of validation, the new transmitarray is modeled and simulated using a MoM-based...
The effect of solder volume on the interfacial reactions between Sn-3.0Ag-0.5Cu solder balls and Cu pads during reflow soldering was investigated. Sn-3.0Ag-0.5Cu solder balls of 200, 300, 400, and 500 μm in diameters were employed to react with Cu pads on PCB with the opening diameter of 250 μm The reflow profile was set to reach a peak temperature of 250 °C and maintain a duration of 45s above the...
Ga2-2xIn2xO3 films with different indium content x [In/(Ga+In) atomic ratio] have been prepared on α-Al2O3 (0001) substrates by the metalorganic chemical vapor deposition (MOCVD) method. The preparation, structural and photoluminescence (PL) properties of the Ga2-2xIn2xO3 films were investigated. The XRD analysis revealed that the film with high Ga content exhibited monoclinic structure of Ga2O3 and...
Aluminum reflectors for the utilization of solar energy were prepared by thermal evaporation in a large-scale industrial production line. The morphology, reflection, and roughness of the specimens were investigated, and the influence of substrates on optical performance was studied with experimental methods. The aluminum films of the reflectors were characterized by the scanning electron microscopy...
This paper investigates the performance of the single slot ring element for Ka-band reflectarray designs. Using the element rotation technique, two Ka-band circularly polarized reflectarray prototypes are designed and implemented, with different thicknesses of the substrate. The bandwidth is significantly enhanced when a thick substrate is used.
The cost of photovoltaic (PV) energy generation has been steadily reduced with the increase of solar cell power conversion efficiency and the drop of manufacturing cost. An effective way of lowering the cost of Si thin film solar cells is to increase the solar panel size by growing thin films on large area substrates, where it is important to maintain uniform film properties to ensure efficient and...
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