Ming-Jyh Hwu

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%.

Single step electron-beam lithography for asymmetric recess and gamma gate in high electron mobility transistor fabrication

We have developed an asymmetric recess etch in conjunction with a gamma metal gate process for the fabrication of high electron mobility transistors (HEMTs). This process is based on direct electron-beam lithography with a single exposure of a three stack poly(dimethylglutarimide) and poly(methylmethacrylate) photoresists. It can modify the voltage drop over a wider region fabricated by the so called wide-recess technique as compared with the conventional approach, while maintaining a low source resistance, to reduce the electric field intensity at the gate edge, and therefore enhance the breakdown voltage. This gate engineering process for the 0.2 μm InAlAs/InGaAs metamorphic HEMTs achieved a 45% off-state breakdown voltage improvement as compared with the traditional bilayer T-gate device.

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.

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.

Novel C-band and K-band 3-D InGaP/InGaAs MMICs using low-k BCB interlayer

A C-band and a K-band In/sub 0.49/Ga/sub 0.51/P/ In/sub 0.15/Ga/sub 0.85/As doped-channel HFET (DCFET) monolithic amplifier were developed and fabricated by using a low-k benzocyclobutene (BCB) interlayer technology. With the photo-sensitive low-k BCB interlayer (/spl epsi/ = 2.7), not only the passivation layer, but the capacitor insulator, via holes, and bridge process of the C-band circuit can be realized simultaneously, where the process complexity and cost can be reduced. Besides, the K-band MMIC utilizes a high impedance BCB CPW microstrip line (Z/sub 0/ = 70 /spl Omega/) for the biasing circuit, and a BCB CPW line (Z/sub 0/ = 50 /spl Omega/) for the RF signal transmission path. The low dielectric constant characteristic of the BCB interlayer is beneficial for common-ground bridge process.

Submicron RIE recessed InGaP/InGaAs doped-channel FETs

High performance submicron In/sub 0.49/Ga/sub 0.51/P/In/sub 0.15/Ga/sub 0.85/As doped-channel heterostructure field effect transistors (HFETs) have been developed and characterized. In order to achieve a high uniformity of device characteristics crossing the wafer, BCl/sub 3/+CHF/sub 3/ reactive ion etching technology in gate-recessed process is applied to fabricate the InGaP/InGaAs doped-channel FETs. The unity current gain cut-off frequency (f/sub T/), maximum frequency of oscillation (f/sub max/), and threshold voltage have been investigated versus the gate-length. The improved microwave performance in smaller gate-length devices is mainly associated with the reduction of the input capacitance. The 0.2 /spl times/ 200-/spl mu/m/sup 2/ gate-dimension DCFET exhibits a saturated P/sub out/ of 18.9 dBm, a power density of 388 mW/mm, a PAE of 35%, and an associated gain of 14 dB at 2.4 GHz.

0.2-/spl mu/m gate-length InGaP-InGaAs DCFETs for C-band MMIC amplifier applications

A C-band In/sub 0.49/Ga/sub 0.51/P-In/sub 0.15/Ga/sub 0.85/As doped-channel FET (DCFET) monolithic power amplifier was designed and fabricated using low-k benzocyclobutene (BCB) interlayer technology. With a photosensitive low-k BCB interlayer (/spl epsiv/=2.7), not only can the circuits passivation layer, but also the capacitor insulator, via holes, and bridge process be realized simultaneously, where the process complexity and cost can be reduced. In addition, a 0.2-/spl mu/m T-shaped gate InGaP-InGaAs doped-channel FET with a high current density and a high linearity is introduced to the amplifier using the e-beam lithography. This C-band power amplifier can achieve a linear power gain of 9.3 dB and an output power of 15.3 dBm, which proves that this novel MMIC process using low-k BCB interlayer technology is attractive for microwave and millimeter wave circuit applications.

High linearity low-k BCB-bridged AlGaAs/InGaAs power HFETs

A novel low-k BCB (benzocyclobutene) bridged and passivated process for AlGaAs/InGaAs doped-channel power FETs with high reliability and linearity was characterized and developed. In this study, we applied the 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 process technique demonstrates a lower power gain degradation under a high input power swing, and exhibits an improved adjacent channel power ratio (ACPR) than the air-bridged ones 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 conventional air-bridged devices.