Improved Linearity in AlGaN/GaN HEMTs for Millimeter-Wave Applications by Using Dual-Gate Fabrication

Abstract

An effective method of improving the linearity of AlGaN/GaN HEMTs by using dual-gate technology is demonstrated. In this letter, we compare the DC characteristics and device linearity of the dual-gate AlGaN/GaN HEMTs with conventional single-gate AlGaN/GaN HEMTs. The correlation between the extrinsic transconductance (G m ) with third-order intermodulation distortion (IM3) and third order intercept point (IP3) suggests that the broader G m distribution as a function of gate-bias, causes a lower IM3 level and higher IP3 values for the device. The improved device linearity demonstrates that dual-gate AlGaN/GaN HEMT design is a good approach for high-linearity RF device applications. AlGaN/GaN based high-electron mobility transistors (HEMTs) have been widely studied for microwave power applications, such as wireless base station and satellite communication owing to the high power handling capability at high frequencies for GaN devices. [1][2][3][4] In modern wireless communication systems, multichannel transmissions are extensively used for signal transmission. During signal transmission, there are many operating frequencies and the neighboring frequencies are located closely to each other, hence the device used in this system will produce the intermodulation distortion and lead to the degradation of the system signal-to-noise ratio (SNR). Among all intermodulation distortions, third-order intermodulation distortion (IM3) dominates the linearity performance of the devices. Hence, IM3 performance is one of the most important criteria for evaluating device performance used in wireless communication systems.Recently, improvement of linearity from the device level is attracting lots of attention. A nonlinearity transfer-function-based analysis method was used for the evaluation of device linearity. 5 In order to reduce IM3, the transconductance needs to remain constant during a wide operating range of the gate bias. It indicates that the flatter transconductance profile results in a lower IM3 levels and a higher third order intercept point (IP3), and thus improves the device linearity. Several methods have been reported in the past to improve the linearity of the GaN HEMTs, including optimizing epitaxial structure 6,7 and utilizing ALD-Al 2 O 3 8 or nanolaminate La 2 O 3 /SiO 2 9 or ferroelectric material of Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) 10 as gate dielectric. In addition, there have been several reports of monolithic microwave integrated circuit (MMIC) low-noise amplifier (LNA) using GaN dual-gate HEMT devices because the two gates allow higher bias operation and increase the transistor output impedance. Moreover, the dual-gate transistors also exhibit smaller feedback capacitance compared to a single-gate transistor.11,12 Furthermore, the dual-gate configuration can be fabricated at the same time as the single-gate configuration using the same process. However, to our best knowledge, there are very few reports on linearity characteristics of dual-gate GaN HEMTs. In this letter, the DC measurements and linearity test ...

A review on GaN HEMTs: nonlinear mechanisms and improvement methods

“…Guidry et al [127] demonstrated a N-polar metal insulator semiconductor (MIS) HEMT with a deep recess gate having OIP3/P DC of 11.4 dB at 30 GHz. In addition, Shrestha et al [128] proposed a N-polar GaN MIS-HEMT simultaneously to achieve a high linearity (OIP3/P DC of 15 dB) and a high gain (12.7 dB) at 30 GHz. Some special structures were also proposed to improve the linearity of the device.…”

Improvement of AlGaN/GaN HEMTs Linearity Using Etched-Fin Gate Structure for Ka Band Applications

“…When it comes to improving the linearity of a HEMT device at very high frequency, i.e., the Ka band, the gate controllability performance, such as the and flatness of the device, becomes the critical factor for the improvement of the device’s linearity characteristics, such as the third-order output intercept point (OIP3) and third-order intermodulation output power (IMD3) [ 19 ]. A low second derivative value of the curve, meaning a flat curve, is favorable for the RF HEMT device to show that the device can withstand the gate voltage swing under high RF input power, keeping the device’s high switching capability as stable as possible [ 20 ]. Researchers have shown that better gate controllability could be achieved by etching AlGaN/GaN device gates along the gate width to form fin-shaped gates, overcoming the deficiencies of small gate length GaN devices, which have exhibited poor gate control over the 2DEG channel [ 21 ].…”

Improvement of DC and f T performances of graded-channel HEMTs by polarization engineering

“…It is worthwhile to mention that several ways have been proposed to overcome the limitations of the poor linearity for GaN HEMTs, such as dual-gate HEMTs [5][6][7], doublechannel structure [8][9][10], δ-doping layer [11][12][13], transitionalrecessed-gate technology [14], polarization doping field effect transistors (PolFETs) [15][16][17][18], and GaN FinFETs [19,20]. Apart from that, the reported graded-channel HEMTs also possess a wider and flatter transconductance [21][22][23].…”