Moo Whan Shin

Thermal modeling and measurement of GaN-based HFET devices

In this letter, we present our thermal study results of GaN-based heterojunction field effect transistors (HFETs). In thermal computation, PAMICE code was used to calculate temperatures in a three-dimension (3-D) model. In the thermal measurement, nematic liquid crystal thermography was employed to determine the peak temperature on the surface of the device chip. The calculated and directly measured temperatures agree well. These methods are valuable in predicting the thermal performance of GaN-based HFET devices, in particular the power devices.

Thermal modeling and measurement of AlGaN-GaN HFETs built on sapphire and SiC substrates

We present thermal modeling and measurement results of AlGaN-GaN heterojunction field effect transistors fabricated on sapphire and SiC substrates, respectively. The device structures are identical except for the substrate material used to grow the AlGaN-GaN heterostructure. One objective is to study the effect of substrate material on the thermal and electrical performance of the resulting devices. To compute the temperature profiles, in-house PAMICE code developed for a three-dimensional structure was used. To measure the temperatures on the chip surface, nematic liquid crystal thermography was used. This technique is nondestructive and can be performed in realtime during device operation. It has submicrometer spatial resolution and /spl plusmn/1/spl deg/C temperature accuracy. The measured temperatures agree well with the calculated ones. The relationship between the measured temperature and power is almost linear for both types of devices. The junction-to-case thermal resistance of the device fabricated on sapphire substrate is 4.4 times that of the device built on SiC substrate.

Synthesis of carbazole-containing PPV and its application to the electroluminescent devices

Abstract Carbazole-containing PPV (CC-PPV) was chemically synthesized and demonstrated to be electroluminescent for application to a light emitting diode (LED). Soluble CC-PPV copolymer was prepared from dialdehyde monomer and diphosphonium salt in a mixed solvent (ethanol/chloroform) by the well-known Wittig reaction. The UV–Vis absorption spectrum of CC-PPV copolymer in chloroform has a maximum absorption wavelength at 408 nm, which is caused by the π–π* transition of the conjugated system. In PL spectrum, maximum wavelength of emission was found at 512 nm. From the thermogravimetric analysis (TGA) it was confirmed that the synthesized CC-PPV has a thermal stability up to 180°C. For the fabrication of a LED, the synthesized CC-PPV was dissolved in toluene to prepare an 1.0 wt% solution and the film cast from this solution was demonstrated to be light-emitting at an applied voltage of 3.7 V.

Thermal study of GaN-based HFET devices

The most important aspects of GaN-based devices are high breakdown field and high operating temperature. One highspeed device structure is the HFET (heterojunction field effect transistor) where two-dimensional electron gas (2DEG) is formed on AlGaN/GaN heterointerface. The electrons in 2DEG have significantly higher mobility than that in the conduction channel of a conventional metal-semiconductor field effect transistor (MESFET). Traditionally, GaN-based devices are fabricated on sapphire substrates. Since the sapphire substrate has relatively low thermal conductivity (0.28 W/cmK), it is necessary to carry out thermal analysis to ensure that the peak operating temperature of the device is within the acceptable range. Much effort has been exerted to provide sufficient thermal analysis in the past. In this paper, we present our thermal simulation using codes previously developed based on analytical solutions in our laboratory and compare the result of thermal simulation to actual thermal measurement results using nematic liquid crystal. Thermal simulation results agree reasonably well with measurement profiles.

Processing Effects of the Polyvinyl-Butyrol-Based Binder on the Performance of Electroluminescent Diodes

Abstract The processing effects of polyvinyl-butyrol (PVB)-based binding organics (PBBO) on the characteristics of the ZnS:Cu electroluminescent (EL) devices are discussed. The characteristics of the EL devices fabricated using the PBBO are compared with those of devices fabricated using a membrane switch composition (MSC). It is demonstrated that the performance of the PBBO be comparable with the MSC. The brightness and the output current of devices using PBBO at 100 V and 400 Hz are 55 cd/m2 and 2.2 mA, respectively. The reliability test performed under the harsh environment (333 K and 90 % RH) exhibits the life time (time at the half of the original brightness) of device longer than 140 hr.