Jin-Cherl Her

SiNx Prepassivation of AlGaN/GaN High-Electron-Mobility Transistors Using Remote-Mode Plasma-Enhanced Chemical Vapor Deposition

The surface of AlGaN/GaN high-electron-mobility transistors (HEMTs) tends to be easily damaged during device fabrication, especially during high-temperature annealing. In order to resolve this problem, a prepassivation process was developed using remote-mode plasma-enhanced chemical vapor deposition (RPECVD) systems. It is important in the prepassivation process to protect the region under the gate during high-temperature ohmic annealing and utilize a low-damage SiNx etching process to minimize any surface damage. It was observed that the DC characteristics were significantly improved and the current collapse phenomenon was markedly suppressed for AlGaN/GaN HEMTs by employing the prepassivation process proposed in this work in comparison with a conventional process. According to the experimental results, the prepassivation process coupled with a gate field plate successfully suppressed the current collapse phenomenon in AlGaN/GaN HEMTs. RF output power densities of 6.9 W/mm at 2.3 GHz and >8.9 W/mm at 4 GHz were achieved for AlGaN/GaN HEMTs on Si and SiC substrates, respectively.

High breakdown voltage GaN Schottky barrier diode employing floating metal rings on AlGaN/GaN hetero-junction

We have reported a lateral GaN SBDs on AlGaN/GaN hetero-junction employing floating metal rings (FMRs) which exhibit a very high breakdown voltage, a low leakage current and a low on-state voltage. We have obtained a very high breakdown voltage of 930V without any additional process step. We have also optimized design parameters of FMR, such as the space between main junction and FMR and the number of rings. Our experimental results show that FMR which is rather simple may be suitable for lateral GaN SBD.

Suppression of Leakage Current of Ni/Au Schottky Barrier Diode Fabricated on AlGaN/GaN Heterostructure by Oxidation

We have proposed and fabricated a lateral GaN Schottky barrier diode (SBD) that increases the breakdown voltage and decreases the leakage current by the oxidation of a Ni/Au Schottky contact. After an oxidation, the anode current was increased under a high anode bias, whereas the turn-on voltage was slightly increased. The leakage current was considerably decreased to less than 1 nA after the oxidations of 5 and 10 min. A high breakdown voltage of 750 V was measured in the proposed GaN SBD when multiple floating metal rings (FMRs) were used for edge termination and oxidation was employed. We have also measured the reverse recovery waveforms at room temperature and 125 °C and the fabricated GaN SBDs show very fast reverse recovery characteristics.

Silicon Dioxide Passivation of AlGaN/GaN HEMTs for High Breakdown Voltage

A new inductively coupled plasma-chemical vapor deposition (ICP-CVD) SiO2 passivation for high voltage switching AlGaN/GaN high electron mobility transistors (HEMTs) is proposed to increase the breakdown voltage and the forward drain current. AlGaN/GaN HEMTs are fabricated and measured before and after SiO2 passivation. The measured off-state breakdown voltage of SiO2 passivated device is 455 V, whereas that of the unpassivated device is 238 V. The surface leakage current of AlGaN/GaN HEMTs are decreased due to SiO2 passivation. The forward drain currents of SiO2 passivated devices are increased by 20 %~35 % because two-dimensional electron gas (2DEG) charge is increased and the electron injections to the surface traps are decreased. SiO2 passivation is more suitable for high voltage switching AlGaN/GaN HEMTs than Si3N4 passivation due to a high breakdown voltage and a low leakage current

A new vertical GaN Schottky barrier diode with floating metal ring for high breakdown voltage

A vertical GaN Schottky barrier diode (SBD) employing a floating metal ring as an edge termination is described. The breakdown voltage is larger than a device without any termination that has been fabricated on a bulk GaN substrate. Fabricated GaN SBD exhibits a high breakdown voltage of 353 V and very fast reverse recovery characteristics of 28 ns. The breakdown voltage of a device without termination is 159 V. It should be noted that the proposed device does not require any additional processes.

AlGaN/GaN High-Electron-Mobility Transistor Employing an Additional Gate for High-Voltage Switching Applications

We have proposed and fabricated an AlGaN/GaN high-electron-mobility transistor (HEMT) with an additional gate, which exhibits a low leakage current and a high breakdown voltage for high-voltage switching applications. The additional gate between the main gate and the drain is specially designed to decrease the electric field concentration at the drain side of the main gate. The leakage current of the proposed HEMT is decreased considerably and the breakdown voltage increases without sacrificing the transconductance and the drain current. The experimental results show that the off-state breakdown voltage and the leakage current of the proposed HEMT are 362 V and 75 nA while those of the conventional HEMT are 196 V and 428 nA, respectively.

An AlGaN/GaN HEMT power switch employing a field plate and a floating gate

We have proposed and fabricated AlGaN/GaN high electron mobility transistors (HEMTs) which increase the gate-drain breakdown voltage by employing a floating gate and a field plate. Experimental results show that the breakdown voltage of the proposed devices was successfully increased compared with that of the devices which employ only the floating gate in our previous report. High breakdown voltage of 484 V is obtained while the breakdown voltage of the conventional devices is 250 V. The leakage current is reduced considerably from 88 to 8.5 μA by employing the additional field plate. Measurement of dynamic characteristics shows that the proposed devices operate under high frequency inductive load switching without any current dispersion.

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.

New Inductively Coupled Plasma–Chemical Vapor Deposition SiO2 Passivation for High-Voltage Switching AlGaN/GaN Heterostructure Field-Effect Transistors

A new inductively coupled plasma–chemical vapor deposition (ICP–CVD) SiO2 passivation for high-voltage switching AlGaN/GaN heterostructure field-effect transistors (HFETs) is proposed to increase the breakdown voltage and forward drain current. The AlGaN/GaN HFETs are fabricated and measured before and after the passivation. The measured off-state breakdown voltage of the passivated device is 455 V, whereas that of the unpassivated device is 282 V. The forward drain currents of the passivated devices are increased by 20–35% because the two-dimensional electron gas (2DEG) concentration is increased and the electron injections to the surface states are decreased.

Electrostatic Discharge Effects on AlGaN/GaN High Electron Mobility Transistors on Sapphire Substrates

The effects of electrostatic discharge (ESD) on the variation of electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs), such as on-current, leakage current of gate and transconductance (gm), have been investigated. The failure phenomena of HEMTs due to the ESD stress have also been studied. We have applied the ESD stress by transmission line pulsing (TLP) method, which is widely used in ESD stress experiments, and measured the electrical characteristics before and after applying ESD stress. The on-current after applying ESD stress was increased because the space between the drain and the gate was narrowed due to the migration of the metal caused by the high electric field and temperature under the ESD stress. The leakage current was decreased and gm was changed slightly. The failure points were located mainly in the middle and on each side of the gate. AlGaN/GaN HEMTs, in contrast with GaAs HEMTs, have been shown to easily fail due to the poor thermal characteristics of the sapphire substrate.