This work analyzes the effect of various gate structures on the DC and radio frequency (RF) performance of AlGaN/GaN high-electron mobility transistors (HEMTs). AlGaN/GaN HEMT devices with a 3 μm drain-to-source spacing, 125 μm gate width and 0.3 μm gate length in various gate structures were fabricated to achieve the desired frequency response with a robust, high yield, and repeatable process. The maximum drain current (I DS , max), maximum DC transconductance (g m), pinch-off voltage (V th), current-gain cutoff frequency (f T), maximum oscillation frequency (f max), and RF characteristics of the devices in terms of the small-signal gain and RF output power (P out) at 8 GHz were investigated. The results showed that the output power is increased by 1 dB when the gate structure is changed from field plate to gamma gate. The V th , g m , f T and f max values are maximized when the thickness of the passivation layer between the gate foot and the gate head is minimized. It is shown that the I DS,max is decreased and P out is increased when the gate recess etching process is performed.
This paper describes an air cavity quad‐flat no‐leads (QFN) over‐molded plastic packaged cascode broadband GaN LNA Monolithic Microwave Integrated Circuit (MMIC) with resistive feedback fabricated with 0.25 μm GaN HEMT technology. The single stage QFN packaged GaN LNA MMIC achieves a bandwidth of 0.03–2.6 GHz with a typical gain of 11.5 dB and less than 1.5 dB noise figure. The low noise amplifier (LNA) design is based on a model of a concept transistor, the cascode transistor used in the design, that has not been fabricated previously. The concept transistor is fabricated for the first time along with the GaN LNA MMIC. The fabricated GaN LNA MMIC is housed in a 12‐lead 3 × 3 mm2 air cavity QFN over‐molded plastic package and mounted on an application board. The measurements taken with the application board represent a good convergence with the design that is based on a concept transistor model. The measurement results and 50 Ω internal matching on both ports without the need for additional matching components make this LNA attractive for many applications.
For the first time, the effect of the gate structure on the kink phenomenon in S22 of the AlGaN/GaN HEMT is investigated in this study. To provide critical understanding into the S22 kink effect, the kink effect in S22 of the AlGaN/GaN HEMTs is investigated with transistors that have various gate lengths (Lg) and gate connected field plate lengths (LgH). The HEMTs are fabricated and characterised at the same conditions, and the equivalent circuit models are used to get consistent results. The experimental results show that the gate structure can play an important role on kink effect in S22. The results present valuable information on the development of the AlGaN/GaN HEMT technology and the MMIC design regarding kink effect.
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