Kyoungchul Jang

Passivation Effects of 100 nm In0.4AlAs/In0.35GaAs Metamorphic High-Electron-Mobility Transistors with a Silicon Nitride Layer by Remote Plasma-Enhanced Chemical Vapor Deposition

In0.4AlAs/In0.35GaAs metamorphic high-electron-mobility transistors (MHEMTs) have been successfully fabricated. In order to reduce the surface effects on the barrier layer, Si3N4 layer passivation by remote plasma-enhanced chemical vapor deposition (PECVD) is utilized, which might suppress the surface trap density in side-recessed region and reduce the parasitic resistance. The device simulation was performed to derive the effects of surface trap in the side-recessed region. As the surface trap density decreases, ID.max increases because of the stabilization of the surface states in the side-recessed region. This result indicates that the increases of gm.max and ID.max are related with both the reduction of parasitic resistance and the gate-sinking effect. The fabricated 100 nm MHEMTs with the passivated of Si3N4 layer exhibited excellent characteristics such as a maximum extrinsic gm.max of 740 mS/mm and a cut off frequency ( fT) of 210 GHz.

High Performance 0.1 µm GaAs Pseudomorphic High Electron Mobility Transistors with Si Pulse-Doped Cap Layer for 77 GHz Car Radar Applications

In this study, 0.1 µm double-recessed T-gate GaAs pseudomorphic high electron mobility transistors (PHEMTs), in which an InGaAs layer and a Si pulse-doped layer in the cap structure are inserted, have been successfully fabricated. This cap structure improves ohmic contact. The ohmic contact resistance is as small as 0.07 Ωmm, consequently the source resistance is reduced by about 20% compared to that of a conventional cap structure. This device shows good DC and microwave performance such as an extrinsic transconductance of 620 mS/mm, a maximum saturated drain current of 780 mA/mm, a cut-off frequency fT of 140 GHz and a maximum oscillation frequency of 260 GHz. The reverse breakdown is 5.7 V at a gate current density of 1 mA/mm. The maximum available gain is about 7 dB at 77 GHz. It is well suited for car radar monolithic microwave integrated circuits (MMICs).

In0.49GaP/Al0.45GaAs barrier enhancement-mode pseudomorphic high electron mobility transistor with high gate turn-on voltage and high linearity

We present an In0.49GaP/Al0.45GaAs barrier enhancement-mode pseudomorphic high electron mobility transistor (E-pHEMT) with a high gate forward turn-on voltage and a high drain current linearity. Device simulation shows that the normally observed transconductance reduction at a high VGS in E-pHEMT with a high gate turn-on voltage is closely related to the low electron carrier density of the gate side recess region to the source. We insert Al0.45GaAs into the barrier for a higher gate forward turn-on voltage and adopt In0.49GaP as an etch stop, which has less surface defects, for a higher transconductance at a high gate bias. The fabricated 0.5 µm E-pHEMT exhibits a gate forward turn-on voltage of 1.05 V, a drain current of 450 mA/mm at Vgs=1.5 V, a high transconductance of 470 mS/mm and a high linearity with gate swing for a transconductance flat region of 0.7 V.

Compact RF Switch ICs Using Dielectric Overhang Gate Process and Stacked Inductor

In this paper, we present a compact quadrate-gate single-pole double-through RF switch. We could reduce the size of the multiple-gate high electron mobility transistor (HEMT) switch by reducing the length of the ohmic electrode and the distance between the source and drain electrodes without a severe degradation of switch performance. We developed the dielectric overhang gate process to reduce the distance between the source and drain electrodes of the multiple-gate HEMT switch. LC resonance using a stacked multilayer inductor was employed for the enhancement of isolation without extra area consumption.

In0.49GaP/Al0.45GaAs E-pHEMT with High Gate Forward Turn-on Voltage & High Transconductance Linearity

We present In0.49Gap/Al0.45GaAs Enhancement-mode pseudomorphic HEMT (E-pHEMT) with high gate forward turn-on voltage and high transconductance linearity. E-pHEMT’s with high gate forward turn-on voltage usually suffer from severe transconductance reduction at high Vgs. The low electron carrier density of ungated region of E-pHEMT, especially of gate side recess region, is closely related to that transconductance reduction. We adopted Al0.45GaAs as a barrier for higher gate forward turn-on voltage and In0.49Gap as an etch stop, which causes less deep levels, for higher transconductance at high gate bias. The gate forward turn-on voltage was around 1.1V. The transconductance of 0.5μm E-pHEMT was over 90% of gm.max for the gate voltage swing of 0.65V.

Compact RF Switches Using Dielectric Overhang Gate Process & Stacked Inductor

In this paper, we present a compact quadrate-gate single-pole double-through RF switch. We could reduce the size of the multiple-gate high electron mobility transistor (HEMT) switch by reducing the length of the ohmic electrode and the distance between the source and drain electrodes without a severe degradation of switch performance. We developed the dielectric overhang gate process to reduce the distance between the source and drain electrodes of the multiple-gate HEMT switch. LC resonance using a stacked multilayer inductor was employed for the enhancement of isolation without extra area consumption. [DOI: 10.1143/JJAP.45.3401]

Transconductance Linearity Improvement of Enhancement-Mode Pseudomorphic HEMT with High Gate Forward Turn-On Voltage

In this paper we discuss the sources of the transconductance reduction of enhancement-mode pseudomorphic high electron mobility transistor (E-pHEMT) at a high gate bias and methods of improving the transconductance at a high gate bias. E-pHEMT usually suffers from severe transconductance reduction at a high gate bias. Our simulation showed that this reduction is mainly due to the low channel carrier density and high access resistance of the ungated region rather than the parasitic MESFET phenomenon. An epi structure that facilitates electron transfer through the barrier layer of the ungated region and self align gate (SAG) process lead to an improvement in transconductance linearity.