Edward Y. Chang

Thermal stability of Cu/Ta/GaAs multilayers

Copper metallization for GaAs was evaluated by using Cu/Ta/GaAs multilayers for its thermal stability. A thin Ta layer of 40 nm was sputtered on the GaAs substrate as the diffusion barrier before copper film metallization. As judged from sheet resistance, x-ray diffraction, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films with GaAs were very stable up to 500 °C without migration into GaAs. After 550 °C annealing, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaAs2. At 600 °C annealing, the reaction GaAs with Ta and Cu formed TaAs, TaAs2, and Cu3Ga, resulting from Cu migration and interfacial instability.

5 mm high-power-density dual-delta-doped power HEMT's for 3 V L-band applications

A high-power-density dual-/spl delta/-doped AlGaAs-InGaAs-GaAs high electron mobility transistor (HEMT) for personal communication applications has been developed. A 5.0 mm gate-width device operating at a drain bias of 3.0 V gave an output power over 1 W. The 1 /spl mu/m gate-length HEMT exhibited a current density of 425 mA/mm at V/sub gs/=0.5 V. The maximum transconductance of the device was 270 mS/mm. The effective knee voltage was as low as 0.3 V. At the class AB operation, the HEMT demonstrated an output power density of 200 mW/mm, 64% power-added efficiency and 18.2 dB linear gain at 900 MHz. This is the highest power density of a dual-/spl delta/-doped AlGaAs-InGaAs-GaAs HEMT reported to date for low voltage (3 V) wireless applications.

High-efficiency and low-distortion directly-ion-implanted GaAs power MESFETs for digital personal handy-phone applications

We report a high-efficiency and low-distortion GaAs power MESFET using direct ion implantation technology for the digital wireless personal handy-phone system (PHS). When qualified by 1.9-GHz /spl pi//4-shifted quadrature phase shift keying (QPSK) modulated PHS standard signals, the 2.2-V-operation device with a gate width (Wg) of 2 mm exhibited a power-added efficiency (PAE) of 57.2 % and an adjacent channel leakage power (P/sub adj/) of -58 dBc at an output power of 21.3 dBm. The MESFET with the optimized direct ion implantation conditions and fabrication process achieved the highest PAE for PHS applications. The low-cost MMIC-oriented direct ion implantation technology has demonstrated the state-of-the-art results for new-generation PHS handsets for the first time.

2-V-operation /spl delta/-doped power HEMT's for personal handy-phone systems

A high-efficiency and high-power-density /spl delta/-doped AlGaAs/InGaAs HEMT with low adjacent channel leakage has been developed for the digital wireless personal handy-phone system (PHS). When qualified by 1.9-GHz /spl pi//4-shifted quadrature phase shift keying (QPSK) modulated PHS standard signals, the 2.0-V-operation HEMT with a 1-mm gate width demonstrated a power-added efficiency of 45.3% and an output power density of 105 mW/mm. This is the highest power density ever reported by power transistors for the PHS. State-of-the-art results for the PHS operating at 2.0 V were achieved by the S-doped power HEMT for the first time.

Study of Schottky contacts on n‐Ga0.51In0.49P by low‐pressure metal‐organic chemical‐vapor deposition

A comprehensive study of the Schottky contacts on Ga0.51In0.49P has been made. The Ga0.51In0.49P epitaxial layer was successfully grown on the GaAs substrate by low‐pressure metal‐organic chemical‐vapor deposition to form a lattice‐matched heterostructure. Three different types of films, including single‐layer metal (Pt, Ni, Pd, Au, Co, Mo, W, Cr, Ti, Al, Ta, and In), metal silicides (WSi2, W5Si3 PtSi, and Pt2Si), and TiW nitrides (TiWNX) as the Schottky contacts metals on Ga0.51In0.49P were studied. Due to the high‐band‐gap nature of Ga0.51In0.49P, the Schottky contacts on Ga0.51In0.49P demonstrate good characteristics. The barrier heights range from 0.79 to 1.19 eV depending on the selection of the metals and the annealing conditions. Among single‐metal films, Pt film demonstrates the best thermal stability. A barrier height of 1.09 eV and an ideality factor of 1.06 were obtained even after the Pt Schottky diode was furnace annealed at 500 °C for 30 min. For refractory compounds, the TiWNX film with the...

A Simple Fabrication Process of T-Shaped Gates Using a Deep-UV/Electron-Beam/Deep-UV Tri-Layer Resist System and Electron-Beam Lithography

A new fabrication process of T-shaped gates has been developed using a deep-UV/electron-beam/deep-UV (DUV/EB/DUV) tri-layer resist system and electron-beam lithography for the first time. The simple process accomplished a submicron T-shaped gate by a single exposure and a single development step. The narrow/wide/narrow opening of the DUV/EB/DUV resist structure can be accurately controlled by the e-beam dosage and the development conditions. Differences in the sensitivities of the DUV resist and the EB resist were investigated. Due to the lower sensitivity of the adopted DUV resist to the electron beam, the smaller opening of the DUV resist layer was obtained. The higher sensitivity of the EB resist resulted in a wider opening in the middle resist layer. A 0.15-µm-gate-length T-shaped gate can be easily formed by the short-process-time and low-production-cost hybrid DUV/EB/DUV resist approach.

High-power-density and high-efficiency atomic-planar-doped AlGaAs/InGaAs quantum-well power high-electron-mobility transistors for 2.4 V medium-power wireless communication applications

A high-power-density and high-efficiency molecular-beam-epitaxy-grown atomic-planar-doped AlGaAs/InGaAs quantum-well power high-electron-mobility transistor (HEMT) was developed for low-voltage medium-power wireless communication applications. The HEMT exhibited a maximum drain current of 420 mA/mm and a maximum transconductance of 275 mS/mm. A two-dimensional electron gas with a high sheet charge density and a high electron mobility in the InGaAs quantum well contributed to the high current density and high transconductance of the HEMT and enhanced the device power performance at low operating voltage. An output power density of 177 mW/mm and a power-added efficiency of 61% were achieved by the 2 mm HEMT at a drain voltage of 2.4 V and a frequency of 900 MHz. At 2.1 V drain voltage and 2.4 GHz frequency, the device demonstrated an output power of 24.4 dBm and a power-added efficiency of 57.4%. An adjacent channel leakage power of -55 dBc was attained for the 1.9-GHz π/4-shifted quadrature phase shift keying modulation when the output power was 22.2 dBm and the drain voltage was 2.4 V.

Highly Selective GaAs/Al0.2Ga0.8As Wet Etch Process for the Gate Recess of Low-Voltage-Power Pseudomorphic High-Electron-Mobility Transistor

A selective wet etch process for the gate recess of the GaAs power pseudomorphic high-electron-mobility transistors (pHEMTs) was developed. The power pHEMTs used in this study were epitaxially grown power Al0.2Ga0.8As/In0.2Ga0.8As pHEMTs with a 250 A GaAs cap layer and a 300 A Al0.2Ga0.8As electron-donating layer. The electron-donating layer was used as the etch-stop layer for the gate recess. A selectivity of 3400:1 was achieved for GaAs/Al0.2Ga0.8As layers using citric acid/tripotassium citrate/hydrogen peroxide etching solutions in this study. This is the highest selectivity for GaAs/AlxGa1-xAs selective etching reported so far. The pHEMTs processed using this selective etching demonstrated good device power performance, and the wet recess process did not cause any contamination or damage to the device. The test data indicates that this selective etch process can be of practical use for forming the gate recess of the power pHEMTs with good device performance and excellent electrical uniformity.

Study of La2O3/HfO2Gate Dielectric for n-InAs Metal-Oxide-Semiconductor Capacitor

In this study, we investigate the composite La2O3/HfO2 high k dielectric as the gate oxide for n-InAs metal-oxide semiconductor (MOS) capacitor. The La2O3 was used for its high k value and HfO2 was used as the diffusion barrier and was deposited between La2O3 and InGaAs to prevent the Inter-diffusion between InAs and La2O3 layers after post deposition annealing (PDA). Finally, we demonstrate the La2O3/HfO2 composite oxide structure as the high K dielectric for n-InAs MOS capacitor with enhanced capacitance for the MOS capacitor.

A Strategic Review of Recent Progress in Metamorphic Quantum Well Based Heterostructure Electronic Devices

Recent expansion in the demand for high performance applications require high performance devices. It can be achieved by utilizing features of the quantum well based heterostructures on metamorphic buffer. Based on this metamorphic technique two electronic devices, named high electron mobility transistors (MHEMTs) & heterojunction bipolar transistors (MHBTs) are the areas of interest now-a-days. This paper reviews the remarkable progress being made in the development of InP based MHEMT & MHBT in the context of material properties, device structures, DC and RF performances for the development of low cost, high performance power amplifier (PA) and low noise amplifier (LNA) with high linearity applications.