Record performance of high-power GaN/Al 0:14 -Ga 0:86 N high-electron mobility transistors (HEMT's) fabricated on semi-insulating (SI) 4H-SiC substrates is reported. Devices of 0.125-0.25 mm gate periphery show high CW power densities between 5.3 and 6.9 W/mm, with a typical power-added efficiency (PAE) of 35.4% and an associated gain of 9.2 dB at 10 GHz. High-electron mobility transistors with 1.5-mm gate widths (12 2 125 m), measured on-wafer, exhibit a total output power of 3.9 W CW (2.6 W/mm) at 10 GHz with a PAE of 29% and an associated gain of 10 dB at the 02 dB compression point. A 3-mm HEMT, packaged with a hybrid matching circuit, demonstrated 9.1 W CW at 7.4 GHz with a PAE of 29.6% and a gain of 7.1 dB. These data represent the highest power density, total power, and associated gain demonstrated for a III-Nitride HEMT under RF drive.
We demonstrated that Sc2O3 thin films deposited by plasma-assisted molecular-beam epitaxy can be used simultaneously as a gate oxide and as a surface passivation layer on AlGaN/GaN high electron mobility transistors (HEMTs). The maximum drain source current, IDS, reaches a value of over 0.8 A/mm and is ∼40% higher on Sc2O3/AlGaN/GaN transistors relative to conventional HEMTs fabricated on the same wafer. The metal–oxide–semiconductor HEMTs (MOS–HEMTs) threshold voltage is in good agreement with the theoretical value, indicating that Sc2O3 retains a low surface state density on the AlGaN/GaN structures and effectively eliminates the collapse in drain current seen in unpassivated devices. The MOS-HEMTs can be modulated to +6 V of gate voltage. In particular, Sc2O3 is a very promising candidate as a gate dielectric and surface passivant because it is more stable on GaN than is MgO.
A new room temperature wet chemical digital etching technique for GaAs is presented which uses hydrogen peroxide and an acid in a two‐step etching process to remove GaAs in approximately 15 Å increments. In the first step, GaAs is oxidized by 30% hydrogen peroxide to form an oxide layer that is diffusion limited to a thickness of 14 to 17 Å for time periods from 15 to 120 s. The second step removes this oxide layer with an acid that does not attack unoxidized GaAs. These steps are repeated in succession until the desired etch depth is obtained. Experimental results are presented for this digital etching technique demonstrating the etch rate and process invariability with respect to hydrogen peroxide and acid exposure times.
three-layer neural network with 15 neurons in the first layer and 11 neurons in the hidden layer reaches an E s 9.31 и rms 10 y3 , and it is able to synthesize filters which satisfy the Ž . requirements of the test set filters. In Figure 2 b , for the sake of brevity, we have only shown the FE analysis of three Ž . filters synthesized by the neural network continuous line Ž . and the original ones coming from the test set dotted line . As is apparent, the synthesized filters and the desired masks match well.It is worth pointing out that the reduced size of both learning and test sets can be allowed because of the extreme simplicity of the chosen filter. A larger learning set and a more sophisticated neural-network structure are required when dealing with more complex filtering devices; nevertheless, the features of this technique remain the same.
IV. CONCLUSIONSIn this communication, a quick approach to microwave filter design is presented. This methodology has been applied to a low-order filtering device, giving good results and costing very little computational time in the neural-network learning process. It is worth mentioning that the versatility of the FE may be very useful to generate training sets for more involved microwave filtering devices. In these latter cases, the combined FErneural-network methodology becomes suitable for saving time during the microwave filter design procedure. Future work will be devoted to the use of this procedure in the case of more complex and different order waveguide and planar technology filtering structures as are required in practical applications.
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