Woo-Chang Choi

Methane Gas Sensing Properties of the Zinc Oxide Nanowhisker-derived Gas Sensor

A low power methane gas sensor with microheater was fabricated by silicon bulk micromachining technology. In order to heat up the sensing layer to operating temperature, a platinum (Pt) micro heater was embedded in the gas sensor. The line width and gap of the microheater was 20 and 4.5 , respectively. Zinc oxide (ZnO) nanowhisker arrays were grown on a sensor from a ZnO seed layer using a hydrothermal method. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growing ZnO nanowhiskers. Temperature distribution of the sensor was analyzed by infrared thermal camera. The optimum temperature for highest sensitivity was found to be although relatively high (64%) sensitivity was obtained even at as low a temperature as . The power consumption was 72 mW at , and only 25 mW at .

A Programmable Compensation Circuit for System-on-Chip Application

This paper presents a new programmable compensation circuit (PCC) for a System-on-Chip (SoC). The PCC is integrated with O.18-J.1m BiCMOS SiGe technology. It consists of RF Design-for-Testability (DFT) circuit, Resistor Array Bank (RAB) and digital signal processor (DSP). To verify performance of the PCC we built a 5-GHz low noise amplifier (LNA) with an on-chip RAB using the same technology. Proposed circuit helps it to provide DC output voltages, hence, making the RF system chain automatic. It automatically adjusts performance of an LNA with the processor in the SoC when it goes out of the normal range of operation. The PCC also compensates abnormal operation due to the unusual PVT (Process, Voltage and Thermal) variations in RF circuits.

H 2 S Micro Gas Sensor Based on a SnO 2 -CuO Multi-layer Thin Film

This paper proposes a micro gas sensor for measuring gas. This is based on a -CuO multi-layer thin film. The sensor has a silicon diaphragm, micro heater, and sensing layers. The micro heater is embedded in the sensing layer in order to increase the temperature to an operating temperature. The -CuO multi layer film is prepared by the alternating deposition method and thermal oxidation which uses an electron beam evaporator and a thermal furnace. To determine the effect of the number of layers, five sets of films are prepared, each with different number of layers. The sensitivities are measured by applying gas. It has a concentration of 1 ppm at an operating temperature of . At the same total thickness, the sensitivity of the sensor with multi sensing layers was improved, compared to the sensor with one sensing layer. The sensitivity of the sensor with five layers to 1 ppm of gas is approximately 68%. This is approximately 12% more than that of a sensor with one-layer.

Highly Productive Process Technologies of Cantilever-type Microprobe Arrays for Wafer Level Chip Testing

This paper describes the highly productive process technologies of microprobe arrays, which were used for a probe card to test a Dynamic Random Access Memory (DRAM) chip with fine pitch pads. Cantilever-type microprobe arrays were fabricated using conventional micro-electro-mechanical system (MEMS) process technologies. Bonding material, gold-tin (Au-Sn) paste, was used to bond the Ni-Co alloy microprobes to the ceramic space transformer. The electrical and mechanical characteristics of a probe card with fabricated microprobes were measured by a conventional probe card tester. A probe card assembled with the fabricated microprobes showed good x-y alignment and planarity errors within and , respectively. In addition, the average leakage current and contact resistance were approximately 1.04 nA and 0.054 ohm, respectively. The proposed highly productive microprobes can be applied to a MEMS probe card, to test a DRAM chip with fine pitch pads.

Ferroelectric Properties of Pb[(Zr,Sn)Ti]NbO 3 Thin Films with Various Composition Ratio

Ferroelectric (PNZST) thin films were deposited by a RF magnetron sputtering on (LSCO)/Pt/Ti//Si substrate using a PNZST target with excess PbO of 10 mole%. The crystallinity and electrical properties of the thin films with various composition ratio were investigated. The thin films deposited at the substrate temperature of and the power of 80 W were crystallized to a perovskite phase after rapid thermal annealing(RTA) at for 10 seconds in air. A PNZST thin films with Ti of 10 mole% showed the good crystallinity and ferroelectric properties. The remanent polarization and coercive field of the PNZST capacitor were about and 50 kV/cm, respectively. The reduction of the polarization after switching cycles was less than 10%.