Linearity improvement in AlGaN/GaN HEMTs using longitudinally-varying gate recess

Abstract This paper reports an effective way of improving the linearity of AlGaN/GaN high electron mobility transistors (HEMTs) by modulating the AlGaN barrier thickness under the gate electrode along its width. This produces an offset in the local equivalent threshold voltage ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="bold-italic">V</mml:mi> <mml:mrow> <mml:mi mathvariant="bold-italic">T</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ), and consequently, the proposed device acts as multiple transistors with a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="bold-italic">V</mml:mi> <mml:mrow> <mml:mi mathvariant="bold-italic">T</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> offset connected in parallel configuration. Due to the resulting <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="bold-italic">g</mml:mi> <mml:mrow> <mml:mi mathvariant="bold-italic">m</mml:mi> <mml:mn mathvariant="bold">3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> cancellation, the new device structure exhibits ten-fold suppressed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="bold-italic">g</mml:mi> <mml:mrow> <mml:mi mathvariant="bold-italic">m</mml:mi> <mml:mn mathvariant="bold">3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> peak compared to conventional planar-gated AlGaN/GaN HEMTs. A linearization of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="bold-italic">C</mml:mi> <mml:mrow> <mml:mi mathvariant="bold-italic">g</mml:mi> <mml:mi mathvariant="bold-italic">s</mml:mi> </mml:mrow> </mml:msub> <mml:mo mathvariant="bold">−</mml:mo> <mml:msub> <mml:mi mathvariant="bold-italic">V</mml:mi> <mml:mrow> <mml:mi mathvariant="bold-italic">G</mml:mi> <mml:mi mathvariant="bold-italic">S</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> curve is also demonstrated. Compact modeling and large signal simulation of the proposed device exhibits 7 dB improvement in the linearity figure-of-merit, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="bold-italic">O</mml:mi> <mml:mi mathvariant="bold-italic">I</mml:mi> <mml:mi mathvariant="bold-italic">P</mml:mi> <mml:mn mathvariant="bold">3</mml:mn> <mml:mrow> <mml:mo mathvariant="bold">/</mml:mo> </mml:mrow> <mml:msub> <mml:mi mathvariant="bold-italic">P</mml:mi> <mml:mrow> <mml:mi mathvariant="bold-italic">D</mml:mi> <mml:mi mathvariant="bold-italic">C</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> at 5 GHz, compared to the conventional planar gated devices. Additionally, around 10 dB suppression in two-tone third-order intermodulation distortion and improved efficiency across 3 dB, 6 dB and 10 dB output power back-offs (OBOs)is observed compared to the conventional planar-gated AlGaN/GaN HEMTs at 5 GHz for deep class AB applications. Hence, the proposed longitudinally-varying gate recess technology is a promising candidate for mm-wave linear and efficient amplifiers, suitable for 5G applications.