Ka Ming Wong

Low-Leakage-Current AlN/GaN MOSHFETs Using

Metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs) were fabricated with an AlN/GaN heterostructure grown on Si substrates. A 7-nm Al₂O₃ serving as both gate dielectric under the gate electrode and passivation layer in the access region was used. It was found that the Al₂O₃ was superior to SiN_x in increasing the 2-D electron gas (2DEG) density and thereby reducing the access resistance. In addition, the off-state leakage current (<i>I</i>_off) in these AlN/GaN MOSHFETs was reduced by four orders of magnitude to 7.6 × 10^-5 mA/mm as a result of the Al₂ O₃ gate dielectric, compared to that of AlN/GaN HFETs. Meanwhile, the subthreshold slope was improved to a nearly ideal value of 62 mV/dec because of the extremely low <i>I</i>_off. The MOSHFETs with 1-μm gate length exhibited good DC characteristics. A maximum drain current of 745 mA/mm and a peak extrinsic transconductance of 280 mS/mm were achieved.

\hbox{Al}_{2}\hbox{O}_{3}

A monolithic high-resolution (individual pixel size 300times300 mum2) active matrix (AM) programmed 8times8 micro-LED array was fabricated using flip-chip technology. The display was composed of an AM panel and a LED microarray. The AM panel included driving circuits composed of p-type MOS transistors for each pixel. The n-electrodes of the LED pixels in the microarray were connected together, and the p-electrodes were connected to individual outputs of the driving circuits on the AM panel. Using flip-chip technology, the LED microarray was then flipped onto the AM panel to create a microdisplay.

for Increased 2DEG

LEDs on Si offer excellent potential of low cost manufacturing for solid state lighting and display, taking advantage of the well-developed IC technologies of silicon. In this paper, we report how the performance of LEDs grown on Si can be improved. Multiple quantum well InGaN LED structure was grown on patterned silicon substrates and circular LEDs 160 µm in radius were processed. Fabricated LEDs were then transferred to an electroplated copper substrate with a reflective mirror inserted by a double-flip transfer process, to improve the light extraction efficiency and heat dissipation. The light output power of LEDs on copper increased by ~80% after the transfer. The operating current before the onset of light output power saturation also increased by 25% because of the good thermal conductivity of copper. The light output power of packaged LEDs on copper was 6.5 mW under 20 mA current injection and as high as 14 mW driven at 55 mA.

Monolithic LED Microdisplay on Active Matrix Substrate Using Flip-Chip Technology

In this letter, we have described the design and fabrication of a novel backlight-unit (BLU)-free full-color light emitting diode (LED) based projector. The prototype used three active matrix addressable light emitting diode on silicon (LEDoS) micro-displays with peak emission wavelengths of 630, 535, and 445 nm. The LEDoS micro-displays were realized by integrating monolithic micro-LED arrays and silicon-based integrated circuits using a flip-chip bonding technique. Since the LEDoS micro-displays are self-emitting, conventional BLUs used in liquid crystal displays were not needed. Using a trichroic prism to combine the light from the three LEDoS chips, we have produced the worlds first three-LEDoS projector. This BLU-free three-LEDoS projector consists of much fewer optical components and has significantly higher light utilization efficiency compared with conventional projectors.

Performance improvement of GaN-based light-emitting diodes grown on patterned Si substrate transferred to copper.

In this paper, we describe the design and fabrication of 360 PPI flip-chip mounted active matrix (AM) addressable light emitting diode on silicon (LEDoS) micro-displays. The LEDoS micro-displays are self-emitting devices which have higher light efficiency than liquid crystal based displays (LCDs) and longer lifetime than organic light emitting diodes (OLEDs) based displays . The LEDoS micro-displays were realized by integrating monolithic LED micro-arrays and silicon-based integrated circuit using a flip-chip bonding technique. The active matrix driving scheme was designed on the silicon to provide sufficient driving current and individual controllability of each LED pixel. Red, green, blue and Ultraviolet (UV) LEDoS micro-displays with a pixel size of 50 μm and pixel pitch of 70 μm were demonstrated. With a peripheral driving board, the LEDoS micro-display panels were programmed to show representative images and animations.

A Novel BLU-Free Full-Color LED Projector Using LED on Silicon Micro-Displays

III-nitride light-emitting diodes (LEDs) grown on Si (111) substrates have the potential of low-cost manufacturing for solid-state lighting and display, by taking advantage of the well-developed IC technologies of silicon. In this letter, LEDs grown on silicon substrates were transferred onto copper substrates, to maximize light extraction and heat dissipation. On Si substrates, 300 × 300 ¿m2 multiple quantum well InGaN LEDs were first grown and processed. The top surface of the fabricated devices was then temporarily bonded to a sapphire wafer and the Si substrate was chemically etched. Ti/Al/Ti/Au layers were deposited on the backside of LEDs. An 80-¿m-thick copper layer was electroplated and the temporary bonding was removed, resulting in LEDs on copper substrate. The optical output power of LEDs on copper increased by ~ 70% as compared to that of the LEDs on silicon. The improved performance was attributed to the removal of the light-absorbing Si substrate and the good thermal conductivity of copper.

360 PPI Flip-Chip Mounted Active Matrix Addressable Light Emitting Diode on Silicon (LEDoS) Micro-Displays

High-performance GaN-based green and yellow light-emitting diodes (LEDs) are grown on SiO2 nanorod patterned GaN/Si templates by metalorganic chemical vapor deposition. The high-density SiO2 nanorods are prepared by nonlithographic HCl-treated indium tin oxide and dry etching. The dislocation density of GaN is significantly reduced by nanoscale epitaxial lateral overgrowth. In addition to the much improved green LED (505 and 530 nm) results, the fabricated yellow (565 nm) InGaN/GaN-based multiquantum well (MQW) LEDs on Si substrates are demonstrated for the first time. High-quality GaN buffer and localized states in MQWs are correlated to obtaining high-efficiency long-wavelength emission in our devices.

Transfer of GaN-Based Light-Emitting Diodes From Silicon Growth Substrate to Copper

This letter reports the design and fabrication of optimized electrode structures for matrix addressable monolithic light-emitting diode arrays. The variation of forward voltages of LED pixels in the same row are greatly reduced from 2.62 V (81.9%) to 0.02 V (0.6%) in an 8×8 LED array. The LED arrays are designed with 8×8 square pixels, 500×500 μm2 with a 50-μm wide gap in between. A 24×24 large-scale blue LED panel is demonstrated with 0.06 V (1.8%) forward voltage variation by integrating nine LED array modules on a 2.2-cm diagonal silicon-based substrate. With a similar concept, a 30×30 green LED micro-display with scaled pixel pitch shows excellent display uniformity.

High-Performance Green and Yellow LEDs Grown on

In this paper, the first full-color active matrix programmable monolithic Light Emitting Diodes on Silicon (LEDoS) displays are fabricated using flip-chip technology. The forward voltage uniformity of the LED pixels was greatly improved by a double-side ground structure. A basic LED micro-array module was fabricated and the AM substrate has scaling-up ability. By integrating a certain number of LED micro-array modules onto a large-scale AM substrate, a large-scale display is obtained. By this scaling-up method, the utilization rate of the LED wafers is increased significantly. The yield of the LED pixels is improved simultaneously. Red, green and blue phosphors were excited by UV light to realize a full-color display.

{\rm SiO}_{2}

Lamb-wave mass-sensors were fabricated with MOCVD-grown GaN-based thin films on silicon substrates. Crystalline GaN provides an alternative choice of material for fabricating Lamb-wave sensors. The advantageous properties of this material include high acoustic velocity, high chemical, mechanical and thermal stability, and the potential to integrate with a wide range of GaN-based devices such as high electron mobility transistor (HEMT) circuits, light emitting diodes (LED) and other photonic devices. We successfully developed GaN-based Lamb-wave mass-sensors in small size (membrane size of ∼1mm × 1mm). The sensors showed good signal strength and mass sensitivity, comparable to other mass-sensors using conventional materials. This novel approach not only allows robust low-cost sensors to be fabricated, but also enables future integration with generic GaN-based devices on the same chip (i.e. lab-on-a-chip).