Chul-Ho Won

High-Performance GaN-Based Nanochannel FinFETs With/Without AlGaN/GaN Heterostructure

Two types of fin-shaped field-effect transistors (FinFETs), one with AlGaN/GaN heterojunction and the other with heavily doped heterojunction-free GaN layer operating in junctionless mode, have been fabricated and characterized. The threshold voltages of both devices shift toward positive direction from large negative value as the fin width decreases. Both devices exhibit high ON-state performance. The heterojunction-free GaN FinFETs show superior OFF-state performance because the current flows through the volume of the GaN channel layer, which can be fully depleted. The proposed GaN nanochannel FinFETs are very promising candidates not only for high performance, but also for high power applications.

New Method of Moving Control for Wireless Endoscopic Capsule Using Electrical Stimuli

In order to control the moving speed of an endoscopic capsule in the human intestine, electrical stimulation method is proposed in this paper. The miniaturized endoscopic capsule with the function of various electrical stimulations has been designed and implemented. An in-vivo animal experiment has been performed to show the ability of controlling the movement speed of the endoscopic capsule according to the level of electrical stimulation. In-vivo experiments were performed by inserting the implemented capsule into a pigs intestinal tract. From the experimental results, the activation of peristaltic movement and the relationship between the moving speed of capsule and the stimulation amplitude could be found. It is shown that the moving speed of capsule in the intestine can be controlled by adjustment of the stimulation level applied in the capsule electrodes. The results of the in-vivo experiment verify that the degree of contraction in the intestinal tract is closely related with the level of stimulating electrical voltage, suggesting that the moving speed of capsule in the human gastrointestinal tract can be controlled by externally adjusting the amplitude of stimulating pulse signal.

AlGaN/GaN FinFET With Extremely Broad Transconductance by Side-Wall Wet Etch

AlGaN/GaN-based fin-shaped field-effect transistors with very steep side-wall have been fabricated by utilizing electron-beam lithography and subsequent anisotropic side-wall wet etch in tetramethyl ammonium hydroxide solution. The investigate device demonstrated extremely broad transconductance (gm) ranging from ~0 to ~8 V at VD = 10 V, which is essential for high linearity device performance. Pulse measurement showed that the device exhibits negligible gate lag, but still suffers from drain lag. The device with LGD of 17 μm exhibited excellent OFF-state characteristic with subthreshold swing of ~58 mV/decade, low OFF-state leakage current of ~10-12 A, and breakdown voltage of ~400 V at VG = -9 V.

Telemetry Capsule for Pressure Monitoring in the Gastrointestinal Tract

In this paper, the pressure monitoring telemetry system has been designed and implemented for an accurate pressure measure-ment inside the gastrointestinal tract with minimizing pain and inconvenience. The system is composed of a miniaturized pres-sure measurement capsule and an external receiver. The per-formance of the telemetry capsule for monitoring pressure in the gastrointestinal tract is demonstrated by the results of animal in-vivo experiments.

Fabrication of the Wireless Systems for Controlling Movements of the Electrical Stimulus Capsule in the Small Intestines

Diseases of the gastro-intestinal tract are becoming more prevalent. New techniques and devices, such as the wireless capsule endoscope and the telemetry capsule, that are able to measure the various signals of the digestive organs (temperature, pH, and pressure), have been developed for the observation of the digestive organs. In these capsule devices, there are no methods of moving and grasping them. In order to make a swift diagnosis and to give proper medication, it is necessary to control the moving speed of the capsule. This paper presents a wireless system for the control of movements of an electrical stimulus capsule. This includes an electrical stimulus capsule which can be swallowed and an external transmitting control system. A receiver, a receiving antenna (small multi-loop), a transmitter, and a transmitting antenna (monopole) were designed and fabricated taking into consideration the MPE, power consumption, system size, signal-to-noise ratio and the modulation method. The wireless system, which was designed and implemented for the control of movements of the electrical stimulus capsule, was verified by in-vitro experiments which were performed on the small intestines of a pig. As a result, we found that when the small intestines are contracted by electrical stimuli, the capsule can move to the opposite direction, which means that the capsule can go up or down in the small intestines.

AlGaN/GaN High Electron Mobility Transistor-Based Biosensor for the Detection of C-Reactive Protein

In this paper, we propose an AlGaN/GaN high electron mobility transistor (HEMT)-based biosensor for the detection of C-reactive protein (CRP) using a null-balancing circuit. A null-balancing circuit was used to measure the output voltage of the sensor directly. The output voltage of the proposed biosensor was varied by antigen-antibody interactions on the gate surface due to CRP charges. The AlGaN/GaN HFET-based biosensor with null-balancing circuit applied shows that CRP can be detected in a wide range of concentrations, varying from 10 ng/mL to 1000 ng/mL. X-ray photoelectron spectroscopy was carried out to verify the immobilization of self-assembled monolayer with Au on the gated region.

Dual-wavelength sensitive AlGaN/GaN metal-insulator-semiconductor-insulator-metal ultraviolet sensor with balanced ultraviolet/visible rejection ratios

We proposed and fabricated a metal-insulator-semiconductor-insulator-metal type dual-wavelength sensitive UV sensor by using an AlGaN/GaN hetero-structure layer epitaxially grown on a sapphire substrate and a thin Al2O3 layer inserted between AlGaN and Ni Schottky electrodes to reduce dark current and improve the UV/visible rejection ratio. The proposed sensor shows high photo-responsive current to both UV wavelength regimes with a significantly improved UV/visible rejection ratio under the regime of the GaN-related UV response. Cut-off wavelengths can be controlled by changing the bias below and above 10 V.

Growth and characterization of semi-insulating carbon-doped/undoped GaN multiple-layer buffer

We have proposed a new semi-insulating GaN buffer layer, which consists of multiple carbon-doped and undoped GaN layer. The buffer layer showed sufficiently good semi-insulating characteristics, attributed to the depletion effect between the carbon-doped GaN and the undoped GaN layers, even though the thickness of the carbon-doped GaN layer in the periodic structure was designed to be very thin to minimize the total carbon incorporation into the buffer layer. The AlGaN/AlN/GaN heterostructure grown on the proposed buffer exhibited much better electrical and structural properties than that grown on the conventional thick carbon-doped semi-insulating GaN buffer layer, confirmed by Hall measurement, x-ray diffraction, and secondary ion mass spectrometry. The fabricated device also showed excellent buffer breakdown characteristics.

CPLD Based Bi-Directional Wireless Capsule Endoscopes

In the case of miniaturized telemetry capsules, such as a capsule endoscope that can acquire and transmit images from the intestines, the size and the power consumption of the module are restricted. In the capsule endoscopes, it is desirable that the control function can capacitate the sampling of digestive fluid and tissue, drug delivery, and locomotion. In this paper, the control function was embodied by bi-directional communication. A CPLD (complex programmable logic device) controller was designed and implemented for the bi-directional communication in capsule endoscope. The diameter of capsule was 12 mm and the length was 30 mm. The performance of implemented capsule was verified by in-vivo animal experiments.

Al(In)N/GaN Fin-Type HEMT With Very-Low Leakage Current and Enhanced

Superior device characteristics have been demonstrated with a novel Al(In)N/GaN-based steep fin-type high electron mobility transistor (HEMT) with a fin width (W_fin) of 120 nm, a fin height (H_fin) of 250 nm, and a gate length (L_G) of 200 nm. The proposed device achieved very low drain leakage(I_off) <; 8×10^-8 A/mm at 7 V and <;1×10^-6 A/mm at 100 V, which is four orders of improvement over I_OFF of conventional Al(In)N/GaN HEMTs. In addition, the device exhibits a high ON-state current (I_ON) of 1.12 A/mm, a steep sub-threshold swing (S) of 63 mV/decade, a low drain-induced barrier lowering of 18.5 mV/V, and a high power-gain cutoff frequency (f_T) of 21 GHz.