It is an object to provide a highly reliable semiconductor device with good electrical characteristics and a display device including the semiconductor device as a switching element. In a transistor including an oxide semiconductor layer, a needle crystal group provided on at least one surface side of the oxide semiconductor layer grows in a c-axis direction perpendicular to the surface and includes an a-b plane parallel to the surface, and a portion except for the needle crystal group is an amorphous region or a region in which amorphousness and microcrystals are mixed. Accordingly, a highly reliable semiconductor device with good electrical characteristics can be formed.

Oxide semiconductor film and semiconductor device

A survey of Gallium Nitride HEMT for RF and high power applications

We report a high-performance normally-off Al2O3/AlN/GaN MOS-channel-high electron mobility transistor (MOSC-HEMT) featuring a monocrystalline AlN interfacial layer inserted between the amorphous Al2O3 gate dielectric and the GaN channel. The AlN interfacial layer effectively blocks oxygen from the GaN surface and prevents the formation of detrimental Ga-O bonds. Frequency-dispersion in C-V characteristics and threshold voltage hysteresis are effectively suppressed, owing to improved interface quality. The new MOSC-HEMTs exhibit a maximum drain current of 660 mA/mm, a field-effect mobility of 165 cm2/V·s, a high on/off drain current ratio of ~1010, and low dynamic on-resistance degradation.

Interface Characterization of Normally-Off Al2O3/AlN/GaN MOS-Channel-HEMTs with an AlN Interfacial Layer

Recent Advances in GaN‐Based Power HEMT Devices

Ultra-thin-barrier (UTB) AlGaN/GaN heterostructure is utilized for fabrication of normally-OFF GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs). The sheet resistance of 2-D electron gas in the UTB Al0.22Ga0.78N(5-nm)/GaN heterostructure is effectively reduced by SiNx passivation grown by low-pressure chemical vapor deposition, from 2570 to $334~\Omega $ /□. The fabricated Al2O3/AlGaN/GaN MIS-HEMTs exhibit normally-OFF behavior with good $V_{\mathrm {TH}}$ uniformity and low $V_{\mathrm {TH}}$ -hysteresis. 20 mm-gate-width power devices featuring a low $R_{\sc {\mathrm{ on}}}$ of $0.75~\Omega $ ( $\text{I}_{\mathrm {D,MAX}} =6.5$ A) are also demonstrated on the platform.

High Uniformity Normally-OFF GaN MIS-HEMTs Fabricated on Ultra-Thin-Barrier AlGaN/GaN Heterostructure

In this letter, a plasma-free etch stop structure is developed for GaN HEMT toward enhancement-mode operation. The self-terminated precision gate recess is realized by inserting a thin AlN/GaN bilayer in the AlGaN barrier layer. The gate recess is stopped automatically at the GaN insertion layer after high-temperature oxidation and wet etch, leaving a thin AlGaN barrier to maintain a quantum well channel that is normally pinched off. With addition of an Al2O3 gate dielectric, quasi normally OFF GaN MOSHEMTs have been fabricated with high threshold uniformity and low ON-resistance comparable with the normally ON devices on the same wafer. A high channel mobility of 1400 cm $^{2}/\textrm {V}\cdot \textrm {s}$ was obtained due to the preservation of the high electron mobility in the quantum-well channel under the gate.

A GaN HEMT Structure Allowing Self-Terminated, Plasma-Free Etching for High-Uniformity, High-Mobility Enhancement-Mode Devices

The invention discloses a field effect transistor, belongs to the technical field of semiconductor devices, and aims to enable a device to have high breakdown voltage and high saturation output current at the same time. The field effect transistor includes a substrate, a channel layer formed on the substrate, a barrier layer formed on the channel layer, a source electrode, a drain electrode and a grid electrode which are formed on the barrier layer, and at least one ohmic contact metal strip formed between the grid electrode and the drain electrode, wherein the source electrode and the drain electrode are located at two sides of the grid electrode respectively. The invention is mainly applied to field effect transistors using III-V compound semiconductors.

Field effect transistor

AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOSHEMTs) with thick (>35 nm), high-κ (TiO2/NiO), submicrometer-footprint (0.4 μm) gate dielectric are found to exhibit two orders of magnitude in lower gate leakage current (~1 nA/mm up to +3-V applied gate bias), higher IMAX (709 mA/mm), and higher drain breakdown voltage, compared to Schottky barrier (SB) HEMTs of the same geometry. The maximum extrinsic transconductance of both the MOSHEMTs and the SBHEMTs with 2 × 80-μm gate fingers is measured to be 149 mS/mm. The addition of the submicrometerfootprint gate oxide layer only results in a small reduction of the current gain cutoff frequency (21 versus 25 GHz, derived from S-parameter test data) because of the high permittivity (κ ≈ 100) of the gate dielectric. This high-performance submicrometer-footprint MOSHEMT is highly promising for microwave power amplifier applications in communication and radar systems.

Low Leakage Current and High-Cutoff Frequency AlGaN/GaN MOSHEMT Using Submicrometer-Footprint Thermal Oxidized TiO 2 /NiO as Gate Dielectric

This letter reports a GaN high-electron mobility transistor (HEMT) with reduced current collapse using a multicycle combined plasma-free ozone oxidation and wet surface treatment before Si3N4 passivation. The surface oxide and decomposed layers could be effectively removed and a perfect AlGaN surface is obtained after the treatment. Pulsed $IV$ and RF power measurement indicate that the current collapse is greatly suppressed due to the removal of imperfect surface layer and damage free nature, providing an effective surface treatment method to improve the effect of passivation in GaN HEMT.

Reduction of Current Collapse in GaN High-Electron Mobility Transistors Using a Repeated Ozone Oxidation and Wet Surface Treatment

In this paper, we propose an air-bridge based on-chip suspended inductor for MMIC application. The quality factor of suspended inductor on sapphire is 10.6 at 4.0 GHz, which is improved by almost 50%, comparing with traditional air-bridge based inductor of the same size. The self-resonance frequency is also improved from 9 GHz to 10 GHz. Several key fabrication processes of this suspended inductor will be presented to illustrate that our method is exactly the same as general air-bridge inductor fabrication processes in MMIC. By analyzing the equivalent circuits of RF inductors, it is shown that the suspended inductor yields lower parasitic capacitance and suffers smaller substrate loss.

Shuxun Lin

Papers

A GaN HEMT Structure Allowing Self-Terminated, Plasma-Free Etching for High-Uniformity, High-Mobility Enhancement-Mode Devices

Field effect transistor

Low Leakage Current and High-Cutoff Frequency AlGaN/GaN MOSHEMT Using Submicrometer-Footprint Thermal Oxidized TiO 2 /NiO as Gate Dielectric

Reduction of Current Collapse in GaN High-Electron Mobility Transistors Using a Repeated Ozone Oxidation and Wet Surface Treatment

A practical suspended spiral inductor for MMIC application