Bong-Ryeol Park

Low Turn-On Voltage AlGaN/GaN-on-Si Rectifier With Gated Ohmic Anode

A novel AlGaN/GaN-on-Si rectifier with a gated ohmic anode has been proposed to reduce the turn-on voltage without breakdown-voltage degradation. The combination of an ohmic anode and a recessed Schottky gate is responsible for the low turn-on voltage and thus increases the forward current. In comparison with conventional Schottky diodes, the forward current at 1.5 V was increased by 2 to 3 times, whereas no breakdown-voltage degradation was observed. The proposed rectifier with an anode-to-cathode distance of 18 μm exhibited a turn-on voltage of 0.37 V, a forward current density of 92 mA/mm at 1.5 V, and a breakdown voltage of 1440 V.

High-Quality ICPCVD

We have developed a high-quality SiO2 deposition process using an inductively coupled plasma chemical vapor deposition system for use as a gate oxide of AlGaN/GaN-on-Si metal-oxide-semiconductor heterostructure field-effect transistor (MOSHFET) for power switching applications. A breakdown field of ~12 MV/cm was achieved using the optimized deposition conditions that were successfully applied in fabrication of the normally off AlGaN/GaN-on-Si MOSHFETs. The fabricated device exhibited excellent characteristics: a maximum drain current density of 375 mA/mm, a threshold voltage of 3 V, and a breakdown voltage of 820 V.

\hbox{SiO}_{2}

We have demonstrated state-of-the-art characteristics of AlGaN/GaN-on-Si heterojunction field effect transistors (HFETs) employing dual field plates. Both gate and drain field plate lengths were optimized in order to maximize the breakdown voltage. Great care was taken not only to optimize the field plate lengths but also to develop processing technologies such as mesa-first prepassivation, a recessed ohmic contact, and a sloped gate. A breakdown voltage of 1590 V with a specific on-resistance of 1.86 mΩ cm2 was achieved for the gate-to-drain distance of 15 µm in which the gate and drain field plate lengths were 2 and 1 µm, respectively.

for Normally Off AlGaN/GaN-on-Si Recessed MOSHFETs

We developed a Schottky barrier diode (SBD) embedded AlGaN/GaN switching transistor to allow negative current flow during off-state condition. An SBD was embedded in a recessed normally-off AlGaN/GaN-on-Si metal-oxide-semiconductor heterostructure field-effect transistor (MOSHFET). The fabricated device exhibited normally-off characteristics with a gate threshold voltage of 2.8 V, a diode turn-on voltage of 1.2 V, and a breakdown voltage of 849 V for the anode-to-drain distance of 8 µm. An on-resistance of 2.66 mΩcm2 was achieved at a gate voltage of 16 V in the forward transistor mode. Eliminating the need for an external diode, the SBD embedded switching transistor has advantages of significant reduction in parasitic inductance and chip area.

State-of-the-Art AlGaN/GaN-on-Si Heterojunction Field Effect Transistors with Dual Field Plates

We have developed a novel unidirectional AlGaN/GaN-on-Si heterojunction field-effect transistor (HFET) with reverse blocking drain. A recessed Schottky contact was incorporated into a conventional ohmic drain electrode to prevent the undesired reverse current flow while reducing the turn-on voltage in forward current characteristics. The combination of recessed Schottky and ohmic electrodes significantly reduced the turn-on voltage in comparison with a conventional Schottky drain. A turn-on voltage of 0.4 V, an off-state forward breakdown voltage of 615 V, and a reverse blocking drain voltage of −685 V were achieved for the gate-to-drain distance of 12 µm.

Schottky barrier diode embedded AlGaN/GaN switching transistor

We have demonstrated a novel AlGaN/GaN power switching device with an embedded Schottky barrier diode. The normally-off transistor mode was implemented with a recessed metal–oxide–semiconductor heterostructure field-effect transistor (MOSHFET) configuration in which a Schottky barrier diode (SBD) was embedded to flow the reverse current. The proposed device is very promising for use in high-efficiency converter and inverter ICs. The prototype device exhibited encouraging characteristics: a turn-on voltage of 2 V for the transistor and a forward turn-on voltage of 0.8 V for the embedded diode. The breakdown voltage for the anode-to-cathode distance of 10 µm was 966 V.

Unidirectional AlGaN/GaN-on-Si HFETs with reverse blocking drain

Thermal effects were investigated in a liquid crystal display (LCD) backlight unit (BLU) that was composed of light emitting diode (LED) arrays. The driving power for a single LED in a BLU is determined by the desired brightness of the LCD panel and the pitch distance between adjacent LEDs. As the pitch distance increases, individual LEDs need to be driven by a higher power in order to maintain the same brightness. Since the junction temperature of an LED plays an important role in LED performance, such as optical efficiency, intensity degradation, and lifetime, the maximum driving power for an LED should be limited by a critical level of the junction temperature. A guideline for designing LED BLU panels taking account of the junction temperature is presented using various parameters of LED arrays.

Normally-Off AlGaN/GaN-on-Si Power Switching Device with Embedded Schottky Barrier Diode

We have developed an AlGaN/GaN-on-Si metal-oxide-semiconductor heterostructure field-effect transistor (MOSHFET) based bidirectional switch with embedded diode bridges for power switching applications. Four Schottky barrier diodes were embedded in an AlGaN/GaN MOSHFET to minimize the parasitic elements and thus reduce the chip area. The fabricated device functioned as a normally OFF, bidirectional switch, where the gate threshold voltage was ~1 V in both forward and reverses modes. The maximum drain current density in forward and reverse operation was ~120 mA/mm with the gate voltage of 12 V. The forward and reverse OFF-state breakdown voltages were 861 and 946 V, respectively.

Thermal consideration in LED array design for LCD backlight unit applications

AbstractIn this study, a novel AlGaN/GaN power-switching device is proposed for use in high-efficiency DC-DC converters. The proposed structure is composed of a normally-off AlGaN/GaN metal-oxide-semiconductor heterojunction field-effect transistor (MOSHFET) and an embedded freewheeling Schottky barrier diode (SBD). The effects of the embedded freewheeling SBD on conversion efficiency were investigated based on circuit simulation of DCDC synchronous buck converters. The SBD embedment not only reduces the chip size and cost, but also improves the power conversion efficiency at high operation frequencies, due to the reduced off-state power loss.

Diode Bridge Embedded AlGaN/GaN Bidirectional Switch

In this study, the effects of forming gas post metallization annealing (PMA) on recessed AlGaN/GaN-on-Si MOSHFET were investigated. The device employed an ICPCVD SiO2 film as a gate oxide layer on which a Ni/Au gate was evaporated. The PMA process was carried out at 350 o C in forming gas