S. C. Foo

Improved two-dimensional electron gas transport characteristics in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor with atomic layer-deposited Al2O3 as gate insulator

The effects of Al2O3 gate insulator grown by atomic layer deposition (ALD) system on the two-dimensional electron gas (2DEG) transport characteristics in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. The shape of the electron lateral distribution in the quantum well at AlGaN/GaN interface was found to be slightly influenced by the Al2O3 thin layer. The drift mobility (μd) of the electrons in ALD-Al2O3/AlGaN/GaN MISHEMT is increased due to the surface passivation effects of the included dielectric layer. The higher dynamic channel current of the MISHEMT indicates that the electron saturation velocity (vsat) is also increased. These results show the improvement of the transport characteristics of 2DEG in Al2O3/AlGaN/GaN MISHEMT by the excellent properties of the Al2O3 grown by ALD.

High Microwave-Noise Performance of AlGaN/GaN MISHEMTs on Silicon With

High microwave-noise performance is realized in AlGaN/GaN metal-insulator semiconductor high-electron mobility transistors (MISHEMTs) on high-resistivity silicon substrate using atomic-layer-deposited (ALD) Al₂O₃ as gate insulator. The ALD Al₂O₃/AlGaN/GaN MISHEMT with a 0.25- ¿m gate length shows excellent microwave small signal and noise performance. A high current-gain cutoff frequency <i>fT</i> of 40 GHz and maximum oscillation frequency <i>f</i> _max of 76 GHz were achieved. At 10 GHz, the device exhibits low minimum-noise figure (NF_min) of 1.0 dB together with high associate gain (<i>Ga</i>) of 10.5 dB and low equivalent noise resistance (<i>Rn</i>) of 29.2 ¿. This is believed to be the first report of a 0.25-¿m gate-length GaN MISHEMT on silicon with such microwave-noise performance. These results indicate that the AlGaN/GaN MISHEMT with ALD Al₂O₃ gate insulator on high-resistivity Si substrate is suitable for microwave low-noise applications.

\hbox{Al}_{2}\hbox{O}_{3}

In this Letter, the device performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) on silicon substrate using 10-nm-thick atomic-layer-deposited ZrO2 as gate dielectrics is reported. The ZrO2 AlGaN/GaN MISHEMTs showed improved maximum drain current density (Idmax) with high peak transconductance (gmmax) as comparison to Schottky-barrier-gate HEMTs (SB-HEMTs). Also compared to SB-HEMTs, reverse gate leakage current was four orders of magnitude lower and forward gate bias extended to +7.4 V. At energy from −0.29 eV to −0.36 eV, low interface trap state density evaluated by AC conductance and “Hi-Lo frequency” methods indicates good quality of atomic-layer-deposited ZrO2 dielectric layer.

Gate Insulator Grown by ALD

Improved device linearity for low-noise applications has been demonstrated in 0.25-μm AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) using atomic-layer-deposited (ALD) Al2O3 as gate dielectric. The measured dc transconductance, microwave small signal, and noise performance feature less dependence on drain current as compared to conventional Schottky-gate AlGaN/GaN HEMTs. Two-tone intermodulation measurement shows that the MISHEMT has a higher value of third-order intercept (IP3). The improved device linearity suggests that the ALD Al2O3/AlGaN/GaN MISHEMT on high-resistivity silicon substrate is promising for high-linearity low-noise amplifier applications.

Atomic layer deposition of ZrO2 as gate dielectrics for AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors on silicon

The influence of electric field (EF) on the dynamic ON-resistance (dyn-RDS[ON]) and threshold-voltage shift (ΔVth) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (IDS-VDS) and drain current (ID) transients. Different EF was realized with devices of different gate-drain spacing (Lgd) under the same OFF-state stress. Under high-EF (Lgd = 2 μm), the devices exhibited higher dyn-RDS[ON] degradation but a small ΔVth (∼120 mV). However, at low-EF (Lgd = 5 μm), smaller dyn-RDS[ON] degradation but a larger ΔVth (∼380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-RDS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔVth. A trap with activation energy 0.33 eV was identified in...

Improved Linearity for Low-Noise Applications in 0.25-

We have demonstrated 0.17-µm gate-length In0.17Al0.83N/GaN high-electron-mobility transistors (HEMTs) on Si(111) substrates using a non-gold metal stack (Ta/Si/Ti/Al/Ni/Ta) with a record-low ohmic contact resistance (Rc) of 0.36 Ω mm. This contact resistance is comparable to the conventional gold-based (Ti/Al/Ni/Au) ohmic contact resistance (Rc = 0.33 Ω mm). A non-gold ohmic contact exhibited a smooth surface morphology with a root mean square surface roughness of ~2.1 nm (scan area of 5 × 5 µm2). The HEMTs exhibited a maximum drain current density of 1110 mA/mm, a maximum extrinsic transconductance of 353 mS/mm, a unity current gain cutoff frequency of 48 GHz, and a maximum oscillation frequency of 66 GHz. These devices exhibited a very small (<8%) drain current collapse for the quiescent biases (Vgs0 = −5 V, Vds0 = 10 V) with a pulse width/period of 200 ns/1 ms. These results demonstrate the feasibility of using a non-gold metal stack as a low Rc ohmic contact for the realization of high-frequency operating InAlN/AlN/GaN HEMTs on Si substrates without using recess etching and regrowth processes.

\mu\hbox{m}

In this paper, a comprehensive study on the effect of plasma-enhanced chemical-vapor-deposited SiN surface passivation on the bias-dependent small-signal equivalent-circuit elements is carried out for AlGaN/GaN high-electron mobility transistors on a high-resistivity silicon substrate. The direct-current and small-signal performance of the device was found to be improved by surface passivation. The small-signal equivalent-circuit parameters at various gate and drain biases were extracted, and the physical mechanisms of their bias-dependent behaviors before and after passivation are discussed in detail.

GaN MISHEMTs Using ALD

Abstract We have investigated the influence of the two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistors (HEMTs) on their reliability under ON-state conditions. Devices stressed in the ON-state showed a faster decrease in the maximum drain current (I Dmax ) compared to identical devices stressed in the OFF-state with a comparable electric field and temperature. Scanning electron microscope (SEM) images of ON-state stressed devices showed pit formation at locations away from the gate-edge in the drain-gate access region. Cross-sectional transmission electron microscope (TEM) images also showed dark features at the AlGaN/SiN interface away from the gate edge. Electron energy loss spectroscopy (EELS) analysis of the dark features indicated the presence of gallium, aluminum and oxygen. These dark features correlate with pits observed in the SEM micrographs. It is proposed that in addition to causing joule heating, energetic electrons in the 2D electron gas contribute to device degradation by promoting electrochemical oxidation of the AlGaN.

\hbox{Al}_{2}\hbox{O}_{3}

Temperature-dependent microwave noise characteristics are presented in an atomic-layer-deposited /AlGaN/GaN metal-insulator-semiconductor high-electron mobility transistor (HEMT) (MISHEMT) on a Si substrate over a wide temperature range from -40 to 200 C. Typical noise parameters, including minimum noise figure , noise equivalent resistance , and associate gain , are measured over the whole temperature range. The conventional Schottky-gate HEMT with the same epistructure is also compared. The temperature dependences of and for the MISHEMT are found to be similar to those for the conventional HEMT, respectively, whereas less temperature dependence of is found in the GaN MISHEMT. The degradation rate of the noise performance of MISHEMT is found to be comparable to that of the other reported GaN HEMTs on SiC and sapphire substrates and also comparable to that of GaAs HEMTs.

as Gate Dielectric

Conventional Schottky-metal gate based GaN HEMTs (SB-HEMTs) suffer undesirable high gate leakage current (I_gleak) issue. To reduce the I_gleak, varieties of gate insulators like Si₃N₄, SiO₂, Al₂O₃, Ga₂O₃, HfO₂, Sc₂O₃ etc. have been demonstrated to obtain high quality metal-insulator-semiconductor (MIS) structure. ZrO₂, with a high dielectric constant (18-25 [1]) and large bandgap (5.2-7.8 eV [2]), is a good candidate for gate insulation layer. Compared with ZrO₂ prepared by other techniques, atomic layer deposited (ALD) technique has the benefits of nanometer scalability, high uniformity, good coverage, low defect density, etc. S. Abermann et al. [3] and A. Alexewicz et al. [4] have reported InAlN/GaN MISHEMTs using ALD ZrO₂. However to-date, comprehensive study was not carried out in AlGaN/GaN MISHEMTs on Si with ALD ZrO₂ as insulator layer. In this paper, we demonstrated AlGaN/GaN MISHEMTs with ALD ZrO₂ as the gate dielectric layer on Si substrate. The use of ALD ZrO₂ dielectrics can effectively suppress the reverse gate leakage current and improve gate voltage up to +5 V.