Sang-hyun Park

Carbon nanotube field emitter arrays having an electron beam focusing structure

An electron beam focusing structure was incorporated into the gated field emitter arrays where the emitters were screen-printed carbon nanotubes. The focusing structure was comprised of 8-μm-thick bulky SiOx focus gate insulator and Cr focus gate, and exhibited negligible leakage between the gate and the focus gate. In current–voltage measurements, it is found that the anode current strongly depends on both the focus gate and the anode bias voltages. Electron beams were focused well at the anode with a slight overfocusing effect, which is due to the wide electron beam divergence from carbon nanotubes. A new focusing structure based on the simulation is proposed to overcome the overfocusing.

Carbon Nanotube-Based Field-Emission Displays for Large-Area and Full-Color Applications.

Single-wall carbon nanotubes (SWNTs) were applied to electron emitters of field-emission displays (FEDs). Large-area FED devices with SWNT emitters were successfully fabricated in a diode mode using screen printing to demonstrate moving color images. They revealed excellent field-emission characteristics of a threshold electric field of approximately 2 V/µm. We have also investigated triode-type FED structures to achieve a high gray scale and high brightness. It was observed that electron emission from carbon nanotube emitters was controlled by the modulation of gate voltages.

Film Bulk Acoustic Resonator Fabrication for Radio Frequency Filter Applications

In this paper, a two-step radio frequency (RF) sputtering deposition technique for piezoelectric ZnO film formation and its successful application for film bulk acoustic resonator (FBAR) devices are presented. Several critical parameters of the RF sputtering process such as deposition pressure, RF power and O2 concentration were studied to clarify their effects on the material characteristics of the ZnO films. The ZnO films deposited by the proposed two-step deposition are shown to have the growth characteristic of strongly preferred orientation toward the c-axis. The FBAR devices with the ZnO films showed a large return loss of ~50 dB at the center frequency of 1.49 GHz. It was also found that the impedance matching of the FBAR could be easily achieved simply by controlling the resonance area of the resonator.

Two-step deposition process of piezoelectric ZnO film and its application for film bulk acoustic resonators

In this article, a two-step deposition technique of piezoelectric zinc oxide (ZnO) film formation using radio-frequency (rf) sputtering and its successful applications for film bulk acoustic resonators (FBAR) are presented. Several critical sputtering process parameters such as deposition pressure, rf power, and O2 concentration were investigated to understand their impacts on the resulting crystal structures and surface morphologies of the ZnO films. The ZnO films formed by the two-step deposition have shown the growth characteristic of the strongly preferred orientation toward c axis. The FBAR with the ZnO films showed a large return loss of ∼50 dB at the center frequency of 1.49 GHz. It was also found that the impedance matching of the FBAR could be easily achieved by simply controlling the resonance area of the resonator.

Improvement of field emission characteristics of carbon nanotubes through metal layer intermediation

A method of fabricating carbon nanotube (CNT)-based field emitters has been studied to improve field emission characteristics. From the supplementary substrate coated with CNTs, CNTs were transferred to the objective substrate through the metal intermediation (MI) layer where the heat and pressure were applied. CNTs were vertically aligned on the objective substrate after removing the supplementary substrate. The field enhancement effect of emitters can be increased by the formation of the sharp edges through CNT transfer process. This MI process allows one to lower the processing temperature below 300 °C and form the patterned CNT emitter arrays.

DNA as a support for glucose oxidase immobilization at prussian blue-modified glassy carbon electrode in biosensor preparation

An amperometric glucose biosensor has been developed using DNA as a matrix of Glucose oxidase (GOx) at Prussian-blue (PB)-modified glassy carbon (GC) electrode. GC electrode was chemically modified by the PB. GOx was immobilized together with DNA at the working area of the PB-modified electrode by placing a drop of the mixture of DNA and GOx. The response of the biosensor for glucose was evaluated amperometrically. Upon immobilization of glucose oxidase with DNA, the biosensor showed rapid response toward the glucose. On the other hand, no significant response was obtained in the absence of DNA. Experimental conditions influencing the biosensor performance were optimized and assessed. This biosensor offered an excellent electrochemical response for glucose concentration in micro mol level with high sensitivity and selectivity and short response time. The levels of the relative standard deviation (RSDs), (<4%) for the entire analyses reflected a highly reproducible sensor performance. Through the use of optimized conditions, a linear relationship between current and glucose concentration was obtained up to 4 x 10(-4) M. In addition, this biosensor showed high reproducibility and stability.

Field emission from carbon nanotube emitters fabricated by the metal intermediation layer

Multiwalled carbon nanotube (MWNT) emitters fabricated by the metal intermediation process were studied. This was intended to allow strong adhesion and high electrical contact between the cathode electrode and MWNT emitters. The process was performed by hot-pressed bonding of a metal layer to a MWNT film surface, where the metal layer was deposited on a main substrate. Through this process, MWNTs have open and sharp ends, and the metal layer and the MWNTs have strong electrical contact. Together with unchanged crystallinity of MWNTs as before the process, these effects improve the field emission properties, resulting in 64% reduction of turn on field and two to three orders of magnitude increase of current density.

Efficient random vector verification method for an embedded 32-bit RISC core

Processors require both intensive and extensive functional verification in their design phase to satisfy their general purposability. The proposed random vector verification method for CalmRISC/sup TM/-32 core meets this goal by contributing complementary assistance for conventional verification methods. It adopts a cycle-accurate instruction level simulator as a reference model, runs simulation in both the reference and the target HDL and reports errors if any difference is found between them. These processes are automatically performed in the unified environment. The instruction level simulator, the core part in the verification environment is able to simulate almost every aspect of RISC processors from functional behavior of each opcode to timing details in the pipeline flow in fast speed. Its design style from microprogramming scheme also makes its structure modular and flexible.

CalmRISC/sup TM/-32: a 32-bit low-power MCU core

Architecting todays embedded processor core faces several important design challenges: low power, high performance, and system-on-a-chip considerations. Moreover, support for high-level language constructs and operating systems becomes increasingly critical for acceptance to various applications. CalmRISC/sup TM/-32 effectively meets these challenges by incorporating a carefully designed instruction set, an energy-efficient pipeline design, debugging support with trace mode/CalmBreaker/sup TM/ (an in-circuit debugger), and a generic, yet efficient coprocessor interface. Using a 0.25 /spl mu/m static CMOS standard cell library and compiled datapath cells, the first implementation of CalmRISC/sup TM/-32 operates at 130 MHz (under worst conditions) and consumes 150 /spl mu/A/MHz at 2.5 V. This paper presents a brief description of the instruction set, the overall microarchitecture, and the coprocessor interface of CalmRISC/sup TM/-32.

Electrochemical Detection of Self-Assembled Viologen Modified Electrode as Mediator of Glucose Sensor

An amperometric glucose biosensor has been developed using viologen derivatives as a charge transfer mediator between a glucose oxidase (GOD) and a gold electrode. A highly stable selfassembled monolayer (SAM) of thiol-based viologen was immobilized onto the gold electrode of a quartz crystal microbalance (QCM) and GOD was immobilized onto the viologen modified electrode. This biosensor response to glucose was evaluated amperometrically in the potential of -300 ㎷. Upon immobilization of the glucose oxidase onto the viologen modified electrode, the biosensor showed rapid response towards glucose. Experimental conditions influencing the biosensor performance, such as pH potential, were optimized and assessed. This biosensor offered excellent electrochemical responses for glucose concentration below μ mol level with high sensitivity and selectivity and short response time. The levels of the RSDs (＜ 5 %) for the entire analyses reflected the highly reproducible sensor performance. A linear calibration range between the current and the glucose concentration was obtained up to 4.5 × 10 -4 M. The detection limit was determined to be 3.0 ×10 -6 M.