Hsiang-Chun Wang

Characteristics of AlGaN/GaN HEMTs With Various Field-Plate and Gate-to-Drain Extensions

AlGaN/GaN high-electron-mobility transistors (HEMTs) with various field-plate (FP) and gate-to-drain distance extensions are fabricated and investigated. Experiments are carried out on 20 transistors. Their ON-state resistance (RON), OFF-state breakdown voltage (VBR), RF performance, and low-frequency noise are measured and studied. The FP extension is found to significantly improve the OFF-state breakdown voltage. However, the FP extension obviously weakens the frequency response and power added efficiency performance, because it increases the feedback Cgd. The FP extension is beneficial to the reduction of the electric field intensity at the gate edge of the device and reduces the probability of the injection of electrons into traps, resulting in the reduction of low- frequency noise.

High-temperature stability of postgrowth-annealed Al-doped MgxZn1-xO films without the phase separation effect

This study investigates the effects of thermal annealing on Al-doped MgxZn1−xO (AMZO) films. AMZO films were deposited by a radio-frequency magnetron sputtering system using a 4 in. ZnO/MgO/Al2O3 (76/19/5 wt. %) target. This study measures and reports the Hall results, x-ray diffraction (XRD), transmittance, and x-ray photoelectron spectroscopy (XPS) data. XRD results show that the ZnO (002) and MgO2 (002) wurtzite peaks in addition to the (111)-cubic peak disappeared after 1000 °C annealing. This indicates the coexistence of two phases in the as-grown AMZO films rebuilt after higher thermal treatment. The absorption edges of these as-grown AMZO films shifted toward the short wavelength of 323 nm under 80% transmittance, implying that band gaps can be tuned by changing the Mg content of the AMZO layer. The XPS spectra of AMZO films were also used to analyze the composition of the as-grown and annealed AMZO films.

GaN lattice matched ZnO/Pr 2 O 3 film as gate dielectric oxide layer for AlGaN/GaN HEMT

In this work, we perform AlGaN/GaN MOS-HEMT by using ZnO/Pr<inf>2</inf>O<inf>3</inf> as gate dielectric. After 600°C annealing, the XRD analysis shows ZnO thin films with highly crystalline characteristics, which exhibit a lattice constant (a=3.2498, c=5.2066) matched to GaN (a=3.1890, c=5.1855). The gate leakage current can be improved significantly by inserting ZnO/Pr<inf>2</inf>O<inf>3</inf> dielectric layer; meanwhile, ZnO/Pr<inf>2</inf>O<inf>3</inf> MOS-HEMT shows superior breakdown voltage performance toward ZnO MOS-HEMT and conventional Ni/Au HEMT. From these results, ZnO/Pr<inf>2</inf>O<inf>3</inf> dielectric is promising for low leakage current of AlGaN/GaN based MOS- HEMT.

Analysis of the Back-Gate Effect in Normally OFF p-GaN Gate High-Electron Mobility Transistor

This paper discusses the impact of the back-gate bias on the dc, low-frequency noise, and dynamic behavior characteristics of a p-GaN gate high-electron mobility transistor on silicon substrate. This paper is investigated to understand the physical mechanisms of the back-gate terminal modulation of normally OFF GaN power devices. When a negative backgate bias VB voltage is applied, the 2-D electron gas channel will get closer to AlGaN/GaN heterointerface and interface scattering, such as interface roughness and alloy-disorder scattering will increases significantly, which may be responsible for the increased ON-state resistance (RON). Meanwhile, the opportunity for the capture of carriers by deep-level traps is reduced and the low-frequency noise is thereby suppressed. Under positive VB bias, RON can be reduced but, according to capacitance-voltage measurements and carrier fluctuations extracted from the low-frequency noise spectra, the transported carriers are obviously trapped by the deep-level.

High Breakdown Voltage and Low Thermal Effect Micromachined AlGaN/GaN HEMTs

This work develops a thermally stable micromachined AlGaN/GaN high-electron mobility transistor (HEMT) with an enhanced breakdown voltage. After removal of the Si substrate beneath the HEMT, a 300-nm SiO2 and a 20-μm copper layer are deposited to form the GaN-on-insulator (G.O.I.) structure. The self-heating at high current that is exhibited by GaN HEMTs that are by previously developed full substrate removal methods is eliminated. The need for complicated substrate-transfer technology is also eliminated, increasing chip package yield. The low frequency noise measurement results also demonstrate that the trap density of the buffer/transition layer is reduced by the removal of the substrate and micromachining of the HEMTs.

A Novel Micromachined AlGaN/GaN Power HEMT With Air-Bridged Matrix Heat Redistribution Layer Design

This letter develops a thermally stable micromachined AlGaN/GaN high electron mobility transistor (HEMT) on an Si substrate with an air-bridged heat redistribution layer design. After removal of the Si substrate beneath the HEMT, a significant breakdown voltage improvement was observed. The drain and source terminals were arranged as the matrix type. The 3 μm-thick Au was adopted for terminals connection and current redistribution layer of the proposed power cell. Compared with the traditional multi-fingers layout, the current density was doubled. In addition, the self-heating phenomenon of power cell was also suppressed by the removal of the substrate and air-bridged matrix layouts.

High-performance, micromachined GaN-on-Si high-electron-mobility transistor with backside diamondlike carbon/titanium heat-dissipation layer

A micromachined AlGaN/GaN high-electron-mobility transistor (HEMT) on a Si substrate with diamondlike carbon/titanium (DLC/Ti) heat-dissipation layers was investigated. Superior thermal conductivity and thermal expansion coefficient similar to that of GaN enabled DLC/Ti to efficiently dissipate the heat of the GaN power HEMT through the Si substrate via holes. This HEMT with DLC design also maintained a stable current density at bending conditions (strain: 0.01%). Infrared thermographic imaging showed that the thermal resistance of standard multi-finger power HEMT layer was 13.6 K/W and it improved to 5.3 K/W because of the micromachining process with a backside DLC/Ti composite layer. Thus, the proposed DLC/Ti heat-dissipation layer realized efficient thermal management in GaN power HEMTs.

ZnO based thin-film transistor with high-κ gadolinium and praseodymium oxide as gate dielectric

In this work, we compare the electrical and radio frequency characteristics of top-gate ZnO TFTs with praseodymium oxide layer (Pr<inf>2</inf>O<inf>3</inf>) and Gadolinium oxide layer (Gd<inf>2</inf>O<inf>3</inf>). The source/drain region of ZnO Thin-film transistor is treated by simple O2 plasma instead of complicated processes, such as ion implantation and activation. By O<inf>2</inf> plasma treatment, the source/drain series resistance successfully reduced. With Pr<inf>2</inf>O<inf>3</inf> and Gd<inf>2</inf>O<inf>3</inf>, high dielectric constant (high-κ) insulator gate dielectrics, gate leakage current, On/OFF current ratio, and radio frequency performance successfully improved to their use for portable, battery powered, and circuit design applications. The coupling of the gate electric field is enhanced by using high-κ gate dielectrics.

Low Surface Traps Induced Noise ZrZnO Thin-Film Transistor Using Field-Plate Metal Technology

This study proposes a high-performance top-gate ZrZnO thin-film transistor (TFT) with a novel field-plate (FP) structure. The experimental results show that the Ion/Ioff ratio of the FP TFT is higher than that of a conventional structure. The leakage current and interface traps are reduced simultaneously. The measured low frequency noise spectra also demonstrated that the flicker noise generated by the surface traps can be suppressed by adopting field-plate metal structure for TFT. The field-plate ZrZnO TFT achieved a threshold voltage (VTH) of 0.5 V and the sub-threshold slope (SS) is 0.21 V/decade. In addition, the Ion/Ioff ratio also reached 2.65?104 and the Hooge parameter, ?H, is in the range, 10-5 to 10-4 which is a comparatively low trap induced noise range compared to previous studies.

Temperature dependency and reliability of through substrate via InAlN/GaN high electron mobility transistors as determined using low frequency noise measurement

The reliability of a InAlN/GaN/Si high electron mobility transistor device was studied using low frequency noise measurements under various stress conditions. By applying the through substrate via (TSV) technology beneath the active region of the device, buffer/transition layer trapping caused by the GaN/Si lattice mismatch was suppressed. In addition, a backside SiO2/Al heat sink material improved thermal stability and eliminated the vertical leakage current of the proposed device. Applying the TSV technology improved the subthreshold swing slope from 260 to 230 mV/dec, owing to the stronger channel modulation ability and reduced leakage current of the device. The latticed-matched InAlN/GaN heterostructure had a stable performance after high current operation stress. The suppression of buffer/transition layer traps of the TSV device is a dominant factor in device reliability after long-term high-electric-field stress.