Yunlong He

EBG Structures with Fractal Topologies for Ultra-Wideband Ground Bounce Noise Suppression

Electromagnetic bandgap (EBG) structures consisting of fractal high impedance topologies and effective bridges are proposed and employed for ultra-wideband (UWB) ground bounce noise (GBN) suppression in power and ground plane pairs. These structures have shown good performance. For the first design utilizing fractal high impedance topology with one iteration and meander lines, it provides −49 dB noise suppression from 202 MHz to 20 GHz. Both simulated and measured results are presented to verify the performance. Furthermore, the GBN suppression behaviors of topologies with different iterations have been studied, and the impact of the power plane with the first design on the signal integrity has also been investigated.

Breakdown voltage and current collapse of F-plasma treated AlGaN/GaN HEMTs

The breakdown and the current collapse characteristics of high electron mobility transistors (HEMTs) with a low power F-plasma treatment process are investigated. With the increase of F-plasma treatment time, the saturation current decreases, and the threshold voltage shifts to the positive slightly. Through analysis of the Schottky characteristics of the devices with different F-plasma treatment times, it was found that an optimal F-plasma treatment time of 120 s obviously reduced the gate reverse leakage current and improved the breakdown voltage of the devices, but longer F-plasma treatment time than 120 s did not reduce gate reverse leakage current due to plasma damage. The current collapse characteristics of the HEMTs with F-plasma treatment were evaluated by dual pulse measurement at different bias voltages and no obvious deterioration of current collapse were found after low power F-plasma treatment.

90 nm gate length enhancement-mode AlGaN/GaN HEMTs with plasma oxidation technology for high-frequency application

High-frequency enhancement-mode (E-mode) AlGaN/GaN high-electron-mobility transistors (HEMTs) with plasma oxidation technology (POT) were fabricated through plasma-enhanced chemical vapor deposition. POT enables the formation of a thin oxide layer in the gate region, which decreases the gate leakage by at least two orders of magnitude compared with conventional recessed gate HEMTs. Ultra-low leakage was achieved in the fabricated device, with Ioff = 9.5 × 10−7 mA/mm and a high ON/OFF ratio of over 109. Good suppression of current collapse was obtained after the application of POT in the access region. The enhancement-mode AlGaN/GaN HEMTs with POT showed an outstanding performance, with a Vth of 0.4 V, a maximum drain current of 965 mA/mm, and an fmax of 272 GHz.

Trap states in enhancement-mode double heterostructures AlGaN/GaN high electron mobility transistors with different GaN channel layer thicknesses

This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98–2.56) × 1012 cm−2 eV−1 is located at ET in a range of (0.37–0.44) eV in the thin sample, while the trap state density of (2.3–2.92) × 1012 cm−2 eV−1 is located at ET in a range of (0.33–0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.

Improved on-state performance of AlGaN/GaN Fin-HEMTs by reducing the length of the nanochannel

In this letter, AlGaN/GaN Fin-HEMTs with different nanochannel geometric parameters were fabricated and characterized. The drain current density, transconductance, and on-resistance were improved by reducing the length of the nanochannel, which was attributed to the modulation of access resistance by changing the length of the nanochannel. The threshold voltage shifted to the positive direction with the decrease in the width of the nanochannel and showed the independence on the length of the nanochannel. With the reduction in the length of the nanochannel, the gate swing was increased by suppressing the increase of source resistance, improving the linearity of transconductance.

Characteristics and threshold voltage model of GaN-based FinFET with recessed gate

In this work, AlGaN/GaN FinFETs with different fin widths have been successfully fabricated, and the recessed-gate FinFETs are fabricated for comparison. The recessed-gate FinFETs exhibit higher transconductance value and positive shift of threshold voltage. Moreover, with the fin width of the recessed-gate FinFETs increasing, the variations of both threshold voltage and the transconductance increase. Next, transfer characteristics of the recessed-gate FinFETs with different fin widths and recessed-gate depths are simulated by Silvaco software. The relationship between the threshold voltage and the AlGaN layer thickness has been investigated. The simulation results indicate that the slope of threshold voltage variation reduces with the fin width decreasing. Finally, a simplified threshold voltage model for recessed-gate FinFET is established, which agrees with both the experimental results and simulation results.

Characterization of bulk traps and interface states in AlGaN/GaN heterostructure under proton irradiation

This paper provides a systematic study on the bulk traps and interface states in a typical AlGaN/GaN Schottky structure under proton irradiation. After 3 MeV proton irradiation with a dose of 5 × 1014 H+/cm2, a positive flat band voltage shift of 0.3 V is observed according to the capacitance-voltage (C-V) measurements. Based on this, the distribution of electrons across AlGaN and GaN layers is extracted. Associated with the numerical calculation, direct experimental evidences demonstrate that the bulk traps within the AlGaN layer dominate the carrier removal effect under proton irradiation. Furthermore, the effects of proton irradiation on AlGaN/GaN interface states were investigated by utilizing the frequency dependent conductance technique. The time constants are extracted, which increase from 1.10–2.53 μs to 3.46–37 μs after irradiation. Meanwhile, it shows that the density of interface states increases from 9.45 × 1011–1.70 × 1013 cm−2·eV−1 to 1.8 × 1012–1.8 × 1013 cm−2·eV−1 with an increase in trap activation energy from 0.34 eV–0.32 eV to 0.41 eV–0.35 eV after irradiation. The Coulomb scattering effect of electron trapping at interface states with deeper energy levels is utilized to explain the mobility degradation in this paper.This paper provides a systematic study on the bulk traps and interface states in a typical AlGaN/GaN Schottky structure under proton irradiation. After 3 MeV proton irradiation with a dose of 5 × 1014 H+/cm2, a positive flat band voltage shift of 0.3 V is observed according to the capacitance-voltage (C-V) measurements. Based on this, the distribution of electrons across AlGaN and GaN layers is extracted. Associated with the numerical calculation, direct experimental evidences demonstrate that the bulk traps within the AlGaN layer dominate the carrier removal effect under proton irradiation. Furthermore, the effects of proton irradiation on AlGaN/GaN interface states were investigated by utilizing the frequency dependent conductance technique. The time constants are extracted, which increase from 1.10–2.53 μs to 3.46–37 μs after irradiation. Meanwhile, it shows that the density of interface states increases from 9.45 × 1011–1.70 × 1013 cm−2·eV−1 to 1.8 × 1012–1.8 × 1013 cm−2·eV−1 with an increase in trap ...

Influence of the built-in electric field induced bby low power fluorine plasma implantation on the reliability of AlGaN-GaNHEMTs

The reliability of traditional T-gate AlGaN/GaN high electron mobility transistor (HEMT) fabricated by the low power fluorine plasma treatment was investigated by applying the off-state high electric field stress. The new electrical degradation phenomenon of AlGaN/GaN HEMT with low power fluorine plasma treatment is discovered. The electrical parameters show a rapid degradation in a short time, and then keeping mostly unchangeable. The migration phenomenon of fluorine ions is further validated by the electron redistribution and breakdown voltage enhancement after off-state stress. Due to fluorines strong electronegativity, the migration of fluorine can induce build-in electric field. Thereby, it would prevent the drift of the subsequent fluorine ions and alleviate further degradation of AlGaN/GaN HEMT.

Influence of thermal annealing on AlGaN/GaN HEMT by fluorine plasma treatment

The influence of thermal annealing on four kinds of AlGaN/GaN high electron mobility transistors (HEMTs) with different fluorine plasma treatment power were compared and analyzed in detail. A thin fluorinated layer between the Schottky metal and the AlGaN barrier layer which produced with fluorine plasma treatment was conformed by the comparison of Schottky reverse gate leakage current before annealing and after annealing. The maximum saturation current and the peak transconductance of HEMTs decreased with the fluorine plasma treatment power increasing before annealing, and they were recovered partially after annealing. The hysteresis of double sweep curves by fluorine plasma treatment was enlarged. F− ions could introduce the acceptor state in the barrier layer, and high temperature could eliminate some trap states introduced by fluorine plasma treatment.

The improvement of breakdown voltage in AlGaN/GaN HEMT by using high-k dielectric La 2 O 3 passivation

The AlGaN/GaN high electron mobility transistor using 30-nm ALD La<inf>2</inf>O<inf>3</inf> passivation has been fabricated. Compared with the non-passivation HEMT, the breakdown voltage Vbr of La<inf>2</inf>O<inf>3</inf> passivation HEMT can be improved from 115 V to 134 V. 2-D simulation is adopted to explain the phenomenon. The reason for enhanced Vbr in La<inf>2</inf>O<inf>3</inf> passivation HEMT is due to high permittivity e<inf>r</inf> of La<inf>2</inf>O<inf>3</inf> dielectric with drain side wall and AlGaN/GaN HEMT can form metal-insulator-semiconductor (MIS) structure which can modulate electric field distribution. Based on the results, the introduction of high-K dielectric passivation can enhance breakdown voltage as well as simplify the process step.