Young Seek Cho

Conducting Polymer Material Characterization Using High Frequency Planar Transmission Line Measurement

A conducting polymer, poly 3-hexylthiophene (P3HT) is characterized with the metal-insulator-semiconductor (MIS) measurement method and the high frequency planar circuit method. From the MIS measurement method, the relative dielectric constant of the P3HT film is estimated to be 4.4. For the high frequency planar circuit method, a coplanar waveguide is fabricated on the P3HT film. When applying +20 V to the CPW on P3HT film, the P3HT film is in accumulation mode and becomes lossy. The CPW on P3HT film is 1.5 dB lossier than the CPW on SiO2 film without P3HT film at 50 GHz.

Development and Characterization of Optimum Heat Sink for 30 W Chip on Board LED Down-Light

An optimum heat sink for a 30 W chip on board (COB) LED down-light is designed, fabricated, and characterized. By using the SolidWorks Flow simulator and thermal analysis software, the thermal characteristics of the optimum heat sink is analyzed. Four different types of heat sink are simulated and an optimum structure of the heat sink is found. The simulated temperature of the heat sink when operating the LED down-light is , which is only a difference of from the measured temperature. In order to reduce the temperature further, a copper spreader is introduced to the heat sink. The temperature of the heat sink with the copper spreader is lower than without the copper spreader.

Development of smart LED lighting system using multi-sensor module and bluetooth low energy technology

A smart LED lighting system is designed and implemented using a multi-sensor module and Bluetooth Low Energy (LE) technology. In order to monitor the environmental information such as ambient light intensity, temperature, and/or activity of human or other objects, a multi-sensor module including an ambient light sensor, temperature sensor, and motion sensor is combined to a microcontroller. By collecting environmental information, the LED lighting system can be controlled automatically. Through the Bluetooth LE technology, a user can monitor the environmental information on a smartphone and/or control the LED lighting system manually. Two features, multi-sensor module and Bluetooth LE, let the LED lighting system be more intelligent, energy efficient, and convenient lighting system.

Novel integration technique for flip-chip bonding circuit in wafer scale packaging

A novel integration technique for flip-chip bonding a circuit in wafer scale packaging is presented. The solder is a multilayered structure which consists of 95 at.% Sn and 5 at.% Au. The metal-to-metal bonding process was carried out around 230degC in air. The solder bond pads have an area of 625mum2 with the height of 2.3mum. To characterize the integration technique a variety of designs for a flip-chip interconnections are fabricated and measured for a flip-chip mounted coplanar waveguide (CPW). Modeled predictions of the design show significant performance improvement can be achieved by considering the impact of the substrate and associated parasitics on the mounted chip and transition region in the design. In this paper, we discuss design, modeling and measurement of wide band transition for flip chipped circuits in wafer scale packaging. A locally scaled flip-chip structure is proposed to compensate effective dielectric constant at the transition part of the interconnect

Design and Implementation of LED Dimming System with Intelligent Sensor Module

An intelligent light emitting diode (LED) dimming system is designed and implemented for energy-saving lighting systems. An LED light bulb is powered by an LED driver controlled by a microcontroller using pulse width modulation (PWM) signals. By changing the duty cycle of the PWM signals, the LED driver generates a driving current of up to 1,000 mA. The current consumption by the LED light bulb exhibits a very linear characteristic that indicates that the level of LED dimming can be finely tuned. Multiple sensors—lighting intensity and ultrasonic range sensors—are combined with the LED dimming system to realize an automatically controllable LED lighting system. The light intensity sensor is capable of sensing ambient light. The ultrasonic range sensor can detect objects from 0.15 to 5.6 m at a resolution of 0.0254 m. The collected information by the light intensity and ultrasonic range sensors is processed by the microcontroller that in turn automatically controls the brightness of the LED light bulb. The algorithm of the software for the LED dimming system is also described.

Development of Ultrabroadband (DC–50 GHz) Wafer-Scale Packaging Method for Low-Profile Bump Flip-Chip Technology

A locally matched flip-chip (LMFC) interconnect that uses a capacitive compensation technique to minimize impedance mismatch in coplanar waveguide lines is described. With an optimum percentage change in capacitance of 55plusmn5%, we observe return loss below 25 dB over 90% of a 50 GHz bandwidth. When compared to a conventional flip-chip method, the minimum performance improvement in return loss is 10 dB and the insertion loss is smooth up to 30 GHz. The LMFC interconnect consists of two micromachined features: 1) an air cavity underneath the chip and 2) local trenches in the transition region of the flip-chip interconnect interface. A comparison of different LMFC interconnect designs to the conventional flip-chip approach is made, and design rules to obtain local trench dimensions are discussed.

High speed digital signal analysis of ultra-broadband micromachined flip-chip interconnect designs

Multi-gigabits digital signal transmission in flip-chip interconnect is studied. It is indicated that a conventional flip-chip (CFC) interconnect has two distinct problems. Adding two micromachined features, air cavity and trenches, can improve the transmission characteristic of the CFC interconnect, which is called locally matched flip-chip (LMFC) interconnect. The measured S-parameters, which are the parameters in the frequency domain, show that the LMFC interconnect has the bandwidth of return loss below 20 dB up to 50 GHz. Based on the frequency domain response, the CFC and LMFC flip-chip interconnects are characterized in the time domain using eye-diagram. The simulated eye-diagram performance of the LMFC interconnect indicates that introducing the air cavity and trench to the CFC interconnect improves the multi-gigabits digital signal transmission significantly and the LMFC interconnect could operate at 40 Gb/s bit rate.

Development of Digital Vacuum Pressure Sensor Using MEMS Analog Pirani Gauge

A digital vacuum pressure sensor is designed, fabricated, and characterized using a packaged MEMS analog Pirani gauge. The packaged MEMS analog Pirani gauge requires a current source to heat up a heater in the Pirani gauge. To investigate the feasibility of digitization for the analog Pirani gauge, its implementation is performed with a zero-temperature coefficient current source and microcontroller that are commercially available. The measurement results using the digital vacuum pressure sensor showed that its operating range is 0.05–760 Torr, which is the same as the measurement results of the packaged MEMS analog pressure sensor. The results confirm that it is feasible to integrate the analog Pirani gauge with a commercially available current source and microcontroller. The successful hybrid integration of the analog Pirani gauge and digital circuits is an encouraging result for monolithic integration with a precision current source and ADCs in the state of CMOS dies.

Design and Implementation of Wireless Sensor Network for Freeze Dryer

A wireless sensor network (WSN) is designed and implemented for a freeze dryer. Freeze-drying technology is widely used in the fields of pharmacy and biotechnology as well as the food and agriculture industries. Taking into account the demand for high-resolution pressure and temperature measurements in a freeze dryer, the proposed WSN has a significant advantage of creating a monitoring environment in a freeze dryer. The proposed WSN uses a ZigBee/IEEE 802.15.4 network with an altimeter module that contains a high-resolution pressure and temperature sensor with a serial digital data interface. The ZigBee network is suitable for low-energy and low-data-rate applications in the field of wireless communication. The altimeter module is capable of sensing pressure in the range of 7.5–975 Torr (10–1300 mbar) and temperature in the range of -40C to 125C with a DC power consumption of 3 W. The implemented WSN is installed in a commercial laboratory freeze dryer in order to demonstrate its functionality and efficiency. A comparison with the temperature profile measured by a thermocouple installed in the freeze dryer reveals that the resolution of the temperature profile measured by WSN is superior to that measured by the thermocouple.

Two-Way Relaying-Based Two-Hop Two-User Multiple-Input Multiple-Output System

In multi-hop communication systems, two-way relaying is one of the solutions to mitigate the spectral efficiency loss caused by a half-duplex transmission. In this paper, a simple two-way relaying scheme is proposed for two-hop two-user multiple input multiple output (MIMO) systems. In the proposed system, a base station and a relay station (RS), both equipped with two antennas, form a point-to-point MIMO channel, while the RS and two single-antenna mobile users form a point-tomultipoint multiuser (MU)-MIMO channel. Numerical examples show that the proposed system achieves a significant sum rate gain as compared to a one-way relaying system as the distance between a relay and the two users decreases. We also show that although we can expand the proposed scheme to more than two users, its performance gain as compared to that of oneway relaying decreases with an increase in the number of users.