Yuelin Wang

Fabrication and characterization of a microsystem for a micro-scale heat transfer study

A micro-system consisting of micro-channels with integrated temperature sensors was successfully designed and fabricated for the study of the heat-transfer properties of fluid flow in micro-domains. Surface micro-machining technology was used to construct the micro-channels with dimensions of about 40 µm × 1.4 µm × 4000 µm. Polysilicon thermistors, 4 µm × 4 µm × 0.4 µm in size were suspended across the channels and directly exposed to the fluid for local temperature measurements. The micro-channels and the micro-sensors were calibrated and the micro-system was characterized. The integrated micro-system performance was theoretically analysed to provide a framework for the interpretation of the experimental data, and the various heat-transfer mechanisms are subsequently discussed.

Design and fabrication of a nanofluidic channel by selective thermal oxidation and etching back of silicon dioxide made on a silicon substrate

Based on the law that the oxidation rate of Si decreases with the oxidation time, a method to fabricate a nanochannel is presented. In this method, the depth of the channel is precisely controlled by the oxidation time. Nanochannels are fabricated with depths of several tens of nanometers, width of 20 µm and lengths of several millimeters. SEM images show that the channel is fabricated well. It is shown that the flow rate increases linearly with the inlet pressure for water, NaCl solution and oil. Besides, the flow rate increases with the temperature. The capillary phenomenon is also observed in the nanochannel.

A novel fabrication method of silicon nano-needles using MEMS TMAH etching techniques

Nano-needles play important roles in nanoscale operations. However, current nano-needle fabrication is usually expensive and controling the sizes and angles is complicated. We have developed a simple and low cost silicon nano-needle fabrication method using traditional microelectromechanical system (MEMS) tetramethyl ammonium hydroxide (TMAH) etching techniques. We take advantage of the fact that the decrease of the silicon etch rate in TMAH solutions exhibits an inverse fourth power dependence on the boron doping concentration in our nano-needle fabrication. Silicon nano-needles, with high aspect ratio and sharp angles θ as small as 2.9°, are obtained, which could be used for bio-sensors and nano-handling procedures, such as penetrating living cells. An analytic model is proposed to explain the etching evolution of the experimental results, which is used to predict the needle angle, length, and etching time. Based on our method, nano-needles with small acute angle θ can be obtained.

Novel structure of passive ring waveguide resonator on silicon substrate

A novel optical waveguide rectangular ring resonator is designed and fabricated in silicon-on-insulator (SOl). The resonator is composed of four straight waveguides connected by four 90° directional change-turning mirrors. This merged structure allows compact size and low loss. The input and output waveguides to couple energy into and out from the resonator are also designed and optimized in this work.

Sacrificial layer etching process in joint channels

A sacrificial layer etching process in joint channels is studied in this paper. If the etching process proceeds from a wide channel to a narrow one, the etching front presents a straight line during the whole process according to the experiments. If the etching process proceeds from a narrow channel connected with a wide channel, it is an arc rather than a straight line when the etching front reaches the wide channel. Some other interesting phenomena are also observed during etching the joint structure. For a narrow–wide channel, the etching rate decreases suddenly near the joint area, while for a wide–narrow channel, the etching rate increases quickly near the joint area and decreases gradually after that. A new model is proposed to explain these phenomena, which is proved to match the experimental data well.

Design of S-band TT&C Transponder for Pico-Satellites

An S-band tracking and control transponder with the weight less than 50g is reported in this work. The transponder employs the unified carrier TT&C (Tracking, Telemetry and control) system of the international standard. Some advanced electronic technologies are used in the transponder to simplify the structure and reduce the weight of the transponder. The receive sensitivity is -80dBm and the output power is lOOmW, making it suitable for LEO satellite with the orbit altitude lower than 1000km.

A Novel Structure of Passive Ring Resonator on Silicon Substrate

A novel structure of optic ring resonator is proposed in this work. The resonator is composed of 4 straight lines of wave-guide to form a squared ring and 4 integrated mirrors in the corners of the square. This structure of resonator avoids the curved wave-guide which is necessary in normal structured resonator. The out and input wave-guides to couple energy into and out from the resonator are also designed and optimized in this work.