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The effects of the parasitic gate capacitance and gate resistance (Rg) on the radiofrequency (RF) performance are investigated in LG = 0.15 μm GaN high‐electron‐mobility transistors with T‐gate head size ranging from 0.83 to 1.08 μm. When the device characteristics are compared, the difference in DC characteristics is negligible. The RF performance in terms of the current‐gain cut‐off frequency (fT) and maximum oscillation frequency (fmax) substantially depend on the T‐gate head size. For clarifying the T‐gate head size dependence, small‐signal modeling is conducted to extract the parasitic gate capacitance and Rg. When the T‐gate head size is reduced from 1.08 to 0.83 μm, Rg increases by 82%, while fT and fmax improve by 27% and 26%, respectively, because the parasitic gate–source and gate–drain capacitances reduce by 19% and 43%, respectively. Therefore, minimizing the parasitic gate capacitance is more effective that reducing Rg in our transistor design and fabrication, leading to improved RF performance when reducing the T‐gate head size. [ABSTRACT FROM AUTHOR]

A 55-nm T-gate high-electron-mobility transistor was fabricated with a quaternary barrier AlGa(In)N/AlN/GaN heterostructure grown on a highly resistive Si substrate. The device shows a maximum current density of 1.25 A/mm, a peak extrinsic dc transconductance of 420 mS/mm, and the cutoff frequencies fT/f\text {max} of 145/220 GHz, which gives a record high value of ( fT\cdot f\text {max}{)}^{1/2} = 178 GHz among the reported GaN-on-Si ratio frequency devices. The Al-rich quaternary barrier featured an incorporation of little indium, which yet significantly improved the crystalline quality, resulting in a record low gate leakage below 10−5 A/mm and a high I \mathrm{\scriptscriptstyle ON}/I \mathrm{\scriptscriptstyle OFF} ratio of 1.78\times 10^5 . [ABSTRACT FROM AUTHOR]

The effects of fringing capacitances on the high-frequency performance of T-gate GaN high-electron mobility transistors (HEMTs) are investigated. Delay time components have been analyzed for gate-recessed InAlN/GaN HEMTs with a total gate length of 40 nm and fT/f\max of 225/250 GHz. It is found that the gate extrinsic capacitance contributes significantly to the parasitic delay—approximately 50% of the total delay in these highly scaled devices. The gate extrinsic capacitance comprises two components: 1) parallel plate capacitances between the T-gate and the surrounding electrodes and 2) the fringing capacitance between the gate stem and the access regions. Detailed study of the gate electrostatics reveals that the later, the fringing capacitance between the T-gate stem and the device access region, ultimately determines the lower limit of the extrinsic capacitance Cext; this minimum Cext can be realized experimentally using a large gate stem height (>200~nm) and employing low-k passivation dielectric. Since the corresponding parasitic delay can be expressed as Cext/gm,{\rm int}, this paper also highlights the importance of maximizing gm,int in ultrascaled HEMTs by adopting strategies to enhance carrier velocity. [ABSTRACT FROM AUTHOR]

Abstract: The operation at frequencies above 100GHz of electronic devices like transistors has been achieved both by using high electron mobility III–V semiconductor materials or heterostructures and by implementing fabrication techniques which strongly reduce parasitic capacitances between the device terminals, without increasing series resistances. The technology has been applied on different GaN high electron mobility transistor epiwafers, and the devices performances analyzed under their DC and RF characteristics, outlining that further semiconductor material optimization is mandatory to fully benefit the sub ¼ micron Gate length for very high frequency operation advantage. [Copyright &y& Elsevier]

The impact of graded Al 0. 05 Ga 0. 95 N sub-channel over the DC characteristics of AlGaN/GaN/AlInN Metal Oxide Semiconductor-High Electron Mobility Transistor (MOS-HEMT) has been investigated here. By placing a field plate over the gate region and forming a T-gated structure, the breakdown characteristics are examined using Sentaurus Technology Computer-Aided Design (TCAD) simulation tool. An analytical study is carried out into the evaluation of various device parameters like drain current, transconductance and threshold voltage. RF parameters like cut-off frequency and gain has also been examined. Various physical models such as hydrodynamic, thermodynamic, piezoelectric polarization, impact ionization models are considered. HfO 2 as an oxide layer directly influences the charge confinement near the Two-Dimensional Electron Gas (2DEG), thereby causing a positive shift in the threshold voltage of the device. T-gated formation of the gate helped in enhancing the breakdown voltage of the device to nearly 750 V. A maximum current drive of 1.79 A/mm mm was obtained for the proposed device, nearly 24% improvement from the conventional Composite-channel (CC) HEMT. The current outcomes and the produced frequency characteristics determines the linearity enhancement occurred in the device, caused due to the graded AlGaN sub-channel below the GaN channel layer. The trade-off between specific on-resistance and breakdown voltage is well preserved by employing a T-gated structure with low normal gate length. The outcomes prove the device to be a prime contender for high power switching as well as large signal applications. • The impact of graded AlGaN sub-channel over the DC characteristics of AlGaN/GaN/AlInN MOS-HEMT has been investigated here. • HfO 2 dielectric directly influences the charge confinement near 2DEG, causing a positive shift in the threshold voltage. • T-gated formation of the gate helped in enhancing the breakdown voltage of the device to nearly 750 V. • A 24% enhancement in current drive is observed when the device is brought in comparison with a conventional CC HEMT. [ABSTRACT FROM AUTHOR]

Depletion-mode quaternary barrier \In0.13\Al0.83\break \Ga0.04\N high-electron-mobility transistors (HEMTs) with regrown ohmic contacts and T-gates on a SiC substrate have been fabricated. Devices with 40-nm-long footprints show a maximum output current density of 1.8 A/mm, an extrinsic dc transconductance of 770 mS/mm, and cutoff frequencies fT/f\max of 230/300 GHz at the same bias, which give a record-high value of \surd fT \cdot f\max = \263\ \GHz among all reported InAl(Ga)N barrier HEMTs. The device speed shows good scalability with gate length despite the onset of short-channel effects due to the lack of a back barrier. An effective electron velocity of \1.36 \times \10^7\ \cm/s, which is comparable with that in the state-of-the-art deeply scaled AlN/GaN HEMTs, has been extracted from the gate-length dependence of fT for gate lengths from 100 to 40 nm. [ABSTRACT FROM PUBLISHER]

A V-band push-push GaN monolithic microwave integrated circuit voltage controlled oscillator (VCO) has been realized based on a 0.2 mum T-gate AlGaN/GaN high electron mobility transistor technology with an fT ~ 65 GHz. The GaN VCO delivered an output power of +11 dBm at 53 GHz with an estimated phase noise of -97 dBc/Hz at 1 MHz offset based on on-wafer measurement. To the best of our knowledge, this is the highest frequency VCO ever reported for GaN technology with a high output power at V-band, without using any buffer amplifier. This work demonstrates the potential of applying GaN technology to millimeter wave band, high power, and low phase noise frequency sources applications. [ABSTRACT FROM PUBLISHER]