Che-Kai Lin

Low Hysteresis Dispersion La2O3 AlGaN ∕ GaN MOS-HEMTs

AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using electron-beam evaporated high-dielectric-constant (high-k) lanthanum oxide layer (La 2 O 3 ) as the gate insulator have been investigated and compared with the traditional GaN HEMTs. The dielectric constant of the La 2 O 3 insulator layer developed in this study was 13.1. In addition, a negligible hysteresis voltage shift in the capacitance-voltage curves can be obtained after high temperature annealing. The compositions and the crystalline structures of La 2 O 3 with different annealing temperatures were observed by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. The La 2 O 3 thin film achieved a good thermal stability after 200, 400, and 600°C postdeposition annealing owing to its high binding energy (835.7 eV) characteristics. Moreover, the gate leakage current of a traditional metal gate GaN HEMT can be suppressed for 1 order of magnitude after inserting a La 2 O 3 insulator between Ni and AlGaN, resulting in a better pulsed-mode operation. The device linearity was also improved due to its flat and wide transconductance (g m ) distribution, which was analyzed by a polynomial curve-fitting technique. Therefore, La 2 O 3 is a potential candidate high-k material for the gate insulator to enhance the GaN-based field effect transistor performance while scaling down the device dimension and device reliability at high power operation.

Comprehensive Study of GaAs MOSFETs Using Gadolinium Oxide and Praseodymium Oxide Layers

The high-dielectric-constant (high-k) gadolinium oxide layer (Gd 2 O 3 ) and praseodymium oxide layer (Pr 2 O 3 ) are demonstrated as gate dielectric insulator materials in GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) using in situ high oxygen flow rate electron-beam deposition technology. The dielectric constants of the Gd 2 O 3 and Pr 2 O 3 layers developed in this study were 9.2 and 9.8, respectively. The Schottky gate turn-on voltages of GaAs MOSFETs with Gd 2 O 3 and Pr 2 O 3 insulators were 2.23 and 2.25 V, respectively, representing an improvement on the conventional p-type high electron mobility transistors (0.85 V). Moreover, the Gd 2 O 3 MOSFETs had a higher thermal stability and thermal linearity than the Pr 2 O 3 MOSFET (temperature range 100-400 K) due to its high binding energy, as revealed by X-ray photoelectron spectroscopy.

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.

Enhanced optical responsivity of InAlAs∕InGaAs metamorphic high mobility electron mobility using indium tin oxide transparent gate technology

The high optical responsivity of a transparent gate metamorphic high electron mobility transistor (TG-MHEMT) on GaAs substrate is demonstrated. The transmittance of a 1.3μm emission wavelength for sputtered indium tin oxide TG-MHEMT gate fingers was 90% after 2min of annealing at 300°C and the sheet resistance was 31.3Ωmm. Compared to the back side illumination of a MHEMT phototransistor, which is beneficial for improving photoresponse, the TG-MHEMT can avoid the inconvenient back side thin-down and polish processes. Experimental results demonstrate that TG-MHEMT has good optical performance at a wavelength of λ=1.3μm and comparable to that of the conventional metal gate MHEMT. The increase in drain current and decrease in threshold voltage caused by the illumination can be explained by the photovoltaic effect beneath the transparent gate. The responsivity of TG-MHEMT is roughly 20.6A∕W for a wavelength of λ=1.3μm.

High Performance AlGaN ∕ GaN HEMT with Lattice Matched ZnO Gate Interlayer

AlGaN/GaN high electron mobility transistor (HEMT) with ZnO gate interlayer layer was proposed in this work. It markedly suppressed the gate leakage current and enhanced microwave performances due to the matched lattice constant for insulator and semiconductor. After 2 min 600°C annealing, the x-ray diffraction analysis indicates that ZnO thin films achieved a highly crystalline characteristic, which exhibited a similar lattice constant (a = 3.2498, c = 5.2066) to GaN (a = 3.1890, c = 5.1855). This ZnO thin film also shows a good thermal stability after 500, 600, and 700°C postdeposition annealing due to its high binding energy ( 1022.35 eV) characteristics. By capacitance―voltage and low-frequency noise measurements, ZnO-gate HEMT shows a negligible hysteresis and a low surface state density. At 2.4 GHz operation, the power-added efficiency (PAE) was 31.27%, and the linear power gain (G p ) was 16.6 dB for ZnO-gate HEMT. In contrary, PAE was 23%, and G p was 14 dB for the conventional device. These measured results elucidated that a high quality ZnO/GaN interface was suitable for developing a high performance GaN HEMT.

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.

GaAs Enhancement-Mode MOSHEMT with Pt/ZrO2/Ti/Au Composited Gate Structure

The properties of a GaAs enhancement-mode metal-oxide-semiconductor high electron mobility transistor (E-MOSHEMT) were demonstrated using an electron-beam deposited Pt/ZrO 2 composited gate structure. X-ray photoelectron spectroscopy was conducted to measure the binding energies of ZrO 2 thin films with various postannealing temperatures, and its structural properties remained stable up to 600°C. A 20 nm thick Pt metal layer between AlGaAs and ZrO 2 was used as a buried metal to control the device threshold voltage (V th ) for the enhancement-mode operation. By calculating the capacitance―voltage (C-V) measured curves, the dielectric constant of ZrO 2 was 12.6 and the voltage shift of the C-V hysteresis phenomena can be reduced to 4.5 mV after 400°C postannealing. Measured load-pull power results have also shown that Zr0 2 E-MOSHEMT achieved a better power added efficiency at a high input swing owing to the gate leakage current reduction. The electron-beam evaporated Pt/ZrO 2 /Ti/Au composited gate MOSHEMT is suitable for high volume production due to its in situ insulator and metal gate deposition in the same chamber.

Optoelectronic Mixer Based on Composite Transparent Gate InAlAs–InGaAs Metamorphic HEMTs

In this study, sputtered indium-tin-oxide (ITO) formed ITO/Au/ITO was used to form composite transparent gate InAlAs-InGaAs metamorphic HEMTs (CTG-MHEMT), with an optoelectronic mixer significantly markedly improved front-side optical coupling efficiency. The proposed CTG-MHEMT exhibits a high responsivity (λ = 1310 nm) of 1.71 A/W under optimal bias conditions. A -3 dB electrical bandwidth of 400 MHz is produced by the photovoltaic effect and dominated by the long lifetime of the excess holes. The -3 dB electrical bandwidth associated with the photoconductive effect is 2.3 GHz, and is determined mainly by the short electron life time. A power gain cut-off frequency (fmax) of CTG-MHEMT of 18.2 GHz was achieved. This value, is much larger than that of TG-MHEMT (14.6 GHz) because Au nano particles improved the gate resistance. The optoelectronic mixing efficiency was enhanced by tuning the gate bias conditions. The CTG-MHEMT optoelectronic mixer is a cost-effective device, and based on the optical and electrical characteristics, is a promising candidate for simplifying the system architecture in fiber-optic microwave transmission applications.

Device performance of AlGaN/GaN MOS-HEMTs using La 2 O 3 high-k oxide gate insulator

AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using La<inf>2</inf>O<inf>3</inf> as gate oxide by electron-beam evaporated have been investigated and compared with the regular HEMTs [1]. The La<inf>2</inf>O<inf>3</inf> thin film achieved a good thermal stability after 200°C, 400°C and 600°C post-deposition annealing due to its high binding energy (835.7 eV) characteristics. Our measurements have shown that La<inf>2</inf>O<inf>3</inf> MOS-HEMTs exhibiting the best characteristics, including the lowest gate leakage current, the largest gate voltage swing, and pulsed-mode operation. In addition, a negligible hysteresis voltage shift in the C-V curve can be improved significantly after high temperatures annealing.

High Thermal Stability AlGaAs/InGaAs Enhancement-Mode pHEMT Using Iridium Buried-Gate Technology

The dc, flicker noise, power, and temperature dependence of AlGaAs/InGaAs enhancement-mode pseudomorphic high electron mobility transistors (E-pHEMTs) were investigated using iridium (Ir) buried-gate technology. Although the conventional platinum (Pt)-buried gate has a high metal work function, which is beneficial for increasing the Schottky barrier height of the E-pHEMT, the high rate of intermixing of the Pt-GaAs interface owing to the effect of the continuous production of PtAs 2 on the device influenced the threshold voltage (V th ) and transconductance (g m ) at high temperatures or over the long-term operation. Variations in these parameters make Pt-gate E-pHEMT-related circuits impractical. Furthermore, a PtAs 2 interlayer produced a serious gate leakage current and unstable Schottky barrier height. This study presents the Ir-GaAs Schottky contact because Ir, buried in GaAs, absorbs surface oxygen atoms, forming IrO 2 after annealing at 200°C. Thermally stable IrO 2 inhibited the overdiffusion of Ir at high temperatures and simultaneously suppressed device flicker noise. The V th of Ir/Ti/Au Schottky gate E-pHEMT was 0.238 V and this value shifted to 0.244 V after annealing at 200°C. However, the V th shifted from 0.084 to 0.231 V after annealing of the Pt/Ti/Au Schottky gate E-pHEMT because the Pt sunk into a deeper channel. The slope of the curve of power gain cutoff frequency (f max ) as a function of temperature was -1.5 X 10 -2 GHz/°C for an Ir/Ti/Au-gate E-pHEMT; it was -6.9 X 10 -2 GHz/°C for a Pt/Ti/Au-gate E-pHEMT. The slight variation in the dc and radio-frequency characteristics of the Ir/Ti/Augate E-pHEMT at temperatures from 0 to 150°C revealed that the Ir-GaAs interface has great potential for high power transistors.