Shih-Cheng Yang

Improved device linearity of AlGaAs/InGaAs HFETs by a second mesa etching

The conventional mesa isolation process in AlGaAs/InGaAs heterostructure FETs results in the gate contacting the exposed highly doped region at the mesa sidewalls, forming a parasitic gate leakage path. In this work, we suppress the gate leakage from the mesa-sidewall and enhance microwave power performance by performing an additional second mesa etching. The device gate leakage characteristics under high-input power swing are particularly investigated to reveal an improvement in device linearity, which is sensitive to the sidewall gate leakage. This modified device (M-HFETs) provides not only a higher linear RF output power but also a lower IM3 product than those characteristics in conventional HFETs.

Enhanced power performance of enhancement-mode Al/sub 0.5/Ga/sub 0.5/As/In/sub 0.15/Ga/sub 0.85/As pHEMTs using a low-k BCB passivation

Surface passivation technology plays an important role, especially in E-mode pHEMTs applications, and a new passivation technology has been proposed in this study. This novel benzocyclobutene (BCB) passivation layer takes advantage of the low dielectric permittivity (2.7) and a low loss tangent (0.0008). In this letter, we not only suppress the gate-to-drain leakage current but also improve the device power performance under a high input power swing by using a BCB passivation layer. The passivated 1.0 /spl mu/m-long gate pHEMTs exhibit a better off-state performance than the unpassivated ones. The maximum output power under a 2.4-GHz operation is 118 mW/mm, with a linear power gain of 11.1 dB and a power-added efficiency is 60%.

AlGaAs/InGaAs heterostructure doped-channel FET's exhibiting good electrical performance at high temperatures

High-power and high-efficiency GaAs heterostructure field-effect transistors (FETs) are attracting tremendous attention in RF power amplifier applications. However, thermal effects can be an important issue in RF power devices, owing to the huge amount of heat generated during their operation. In this paper, the temperature-dependent characteristics of Al/sub 0.3/Ga/sub 0.7/As/In/sub 0.15/Ga/sub 0.85/ As doped-channel FETs (DCFETs) are investigated and compared with conventional pseudomorphic-HEMTs (pHEMTs) devices, in terms of their dc, microwave and RF power performance at temperatures ranging from room temperature to 150/spl deg/C. Due to conducting carriers being less influenced by temperature and the better Schottky diode characteristics that can be obtained in DCFETs, the intrinsic device parameters and output performance remain almost constant at high temperatures, which also results in better device reliability. The performance variation of DCFETs associated with temperatures from 25/spl deg/C to 150/spl deg/C all fall within a single digit, i.e., output power (P/sub out/, 16.2 dBm versus 15.8 dBm), power gain (G/sub p/, 16.6 dB versus 15.1 dB), power added efficiency (PAE, 34.2% versus 31.3%), which is not the case for conventional pHEMTs. Therefore, DC devices are very promising for microwave power device applications operating at high temperature.

High performance BCB-bridged AlGaAs/InGaAs power HFETs

A novel low-k benzocyclobutene (BCB) bridged and passivated layer for AlGaAs/InGaAs doped-channel power field effect transistors (FETs) with high reliability and linearity has been developed and characterized. In this study, we applied a low-k BCB-bridged interlayer to replace the conventional air-bridged process and the SiN/sub x/ passivation technology of the 1 mm-wide power device fabrication. This novel and easy technique demonstrates a low power gain degradation under a high input power swing, and exhibits an improved adjacent channel power ratio (ACPR) than those of the air-bridged one, due to its lower gate leakage current. The power gain degradation ratio of BCB-bridged devices under a high input power operation (P/sub in/ = 5 /spl sim/ 10 dBm) is 0.51 dB/dBm, and this value is 0.65 dB/dBm of the conventional air-bridged device. Furthermore, this novel technology has been qualified by using the 85-85 industrial specification (temperature = 85 C, humidity = 85%) for 500 h. These results demonstrate a robust doped-channel HFET power device with a BCB passivation and bridged technology of future power device applications.

A novel double-recessed 0.2-μm T-gate process for heterostructure InGaP-InGaAs doped-channel FET fabrication

A double-recessed T-gate process has been successfully developed to fabricate 0.2-/spl mu/m gate-length heterostructure InGaP-InGaAs doped-channel FETs (DCFETs) to increase the gate-to-drain breakdown voltage. This technology uses direct electron-beam lithography with a single exposure of a four-layer stack polymethylmethacrylate and polydimethylmethacrylate (photoresists). After the combination of chemical and dry etchings, the double gate-recessed DCFETs exhibit improved DC and RF power performance, as compared with the conventional ones, resulting from the gate-leakage current. The Schottky gate breakdown voltage enhances from 5 to 7 V, and the output power increases from 148 to 288 mW/mm at 5.2 GHz.

(Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P/In/sub 0.15/Ga/sub 0.85/As (x=0, 0. 3, 1. 0) heterostructure doped-channel FETs for microwave power applications

The quaternary (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P (0/spl les//spl times//spl les/1) compounds on GaAs substrates are important materials used as a Schottky layer in microwave devices. In this report, we systematically investigated the electrical properties of quaternary (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P materials and concluded that the best composition for improving the device performance is by substituting 30% (x=0.3) of Ga atoms for Al atoms in GaInP material. The Schottky barrier heights (/spl phi/B) of (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P layers were 0.85/spl sim/1.00 eV. We successfully realized the (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P/In/sub 0.15/Ga/sub 0.85/As (x=0, 0.3, 1.0) doped-channel FETs (DCFETs) and demonstrated excellent dc, microwave, and power characteristics.

RIE gate-recessed (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P/InGaAs double doped-channel FETs using CHF 3 +BCl 3 mixing plasma

BCl/sub 3/+CHF/sub 3/ gas mixtures for the reactive ion etching process were applied to the gate-recess for fabricating (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P quaternary heterostructure double doped-channel FETs (D-DCFET), where a high uniformity of Vth was achieved. With the merits of this wide bandgap (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P layer, microwave power performance of this heterostructure D-DCFET demonstrates a compatible performance for devices fabricated on AlGaAs/InGaAs heterostructures.

Improved Gate Leakage and Microwave Power Performance by Inserting A Thin Praseodymium Gate Metal Layer in AlGaAs/InGaAs Doped-Channel Field Effect Transistors

The Praseodymium (Pr) inserted gate AlGaAs/InGaAs heterostructure doped-channel field effect transistors (DCFETs) exhibit improved dc and rf power performance, as compared with the conventional ones, resulting from the gate leakage current reduction. The Schottky gate breakdown voltage enhances from 8 V to 15 V, and a power-added efficiency (PAE) improves from 38% to 43% at 1.8 GHz.

K-band monolithic InGaP-InGaAs DCFET amplifier using BCB coplanar waveguide technology

A K-band (20 GHz) monolithic amplifier was developed and fabricated by adopting a low-/spl kappa/ benzocyclobutene (BCB) coplanar waveguide (CPW) line and InGaP-InGaAs doped-channel HFETs (DCFETs). This monolithic microwave integrated circuit (MMIC) utilizes a high impedance BCB CPW microstrip line (Z/sub 0/=70 /spl Omega/) for the biasing circuits, and a Z/sub 0/=50 /spl Omega/ line for the RF signal transmission. The low dielectric constant characteristic of the BCB interlayer is beneficial for a common-ground bridge process, which reduces the parasitics. The calculated loss tan/spl delta/ is 0.036 for the BCB at 20 GHz. The one-stage MMIC amplifier achieves an S/sub 21/ of 5 dB at 20 GHz, which is the first demonstration of the K-band InGaP-InGaAs DCFET monolithic circuit.

A capacitive peaking of InGaP/GaAs HBT transimpedance amplifier

Integrated InGaP/GaAs HBT transimpedance amplifier (TZ) circuits were designed, fabricated and characterized. In this study, we propose using a capacitive-peaking (C-peaking) technique to increase the bandwidth of the transimpedance amplifier. Based on a Butterworth-type approach, we can easily enhance the bandwidth of the amplifier by this C-peaking technique without sacrificing its low-frequency TZ gain. The low-frequency transimpedance gain of our designed amplifier is 51.4 dB/spl Omega/, and the measured 3 dB bandwidth is enhanced from 9 GHz to 11.8 GHz.