Chang-Taeg Seo

Fabrication of circular-type microchannel using photoresist reflow and isotropic etching for microfluidic devices

In this study, we fabricated circular channels using photoresist reflow and isotropic etching. A silicon substrate, using Si3N4 as a mask, was selectively etched using the hydrofluoric acid, nitric acid, acetic acid (HNA) etching system for fabricating the bottom hemisphere of the channels. Photoresist reflow was used to make the top of the channels round. Then Si3N4 was deposited on the reflowed photoresist. Since the deposited Si3N4 was approximately 6000 A thick, it was possible to observe the inside of the channel. We expect to apply such circular channels to simple bio-systems and microfluidic devices in which optical detection is required.

Fabrication of micro-probe beam using MEMS technology for new vertical silicon probe card

A silicon micro probe beam using a curled cantilever was designed and fabricated using microelectromechanical systems (MEMS) technology, such as porous silicon micromachining, reactive ion etching (RIE) and Au electroplating. The stress analysis of a micromachined micro probe beam was performed using finite-element ANSYS software. As a result, the basic structure was a multilayer composed of Au/Ni–Cr/Si3N4/n-epi layers. The width and length of the micro probe beam were 40 µm and 600 µm, respectively. Annealing is performed for 20 min at 500°C. The result shows that a deflection over 130 µm can be achieved for a silicon epitaxial layer 5 µm thick. The contact resistance of the micro probe beam was less than 2 Ω.

A Novel Comb-Type Differential Pressure Sensor with Silicon Beams Embedded in a Silicone Rubber Membrane

A novel differential pressure sensor has been developed with silicon beams embedded in a silicone rubber membrane. The transducer is usable for most applications involving exposure to harsh media. A piezoresistive differential pressure sensor using silicone rubber membrane has been fabricated on the selectively diffused (100)-oriented n/n+/n silicon substrates by a unique silicon micro-machining technique using porous silicon etching. The pressure sensitivity is about 4.75 mV/kPa and the non-linearity is less than 1.05% FS (full scale).

Characteristics of cantilever beam fabricated by silicon micromachining for flow sensor application

In this paper we report the thermal stress characteristics of multiarray cantilever beam and the result of experimental researches. The cantilever beam was fabricated using porous silicon micromachining techniques, surface tension and the difference in the thermal expansion coefficients between the two films on the cantilever beam. Then the height of the curled cantilever beam is measured as a function of the annealing temperature and time. Using these results, Piezoresistive flow sensors with micro cantilever structure were fabricated using (100), n/n/sup +//n three layer silicon wafer and their characteristics were then investigated. The proposed micro flow sensor consists of four identical silicon cantilever beam with piezoresistors. The total resistance and sheet resistance were obtained about 1K/spl Omega/ and 50/spl Omega/ respectively. The results show the dependence of the sensitivity on cantilever length and geometry.

Fabrication of cylinder type micro channel using photoresist reflow and isotropic etching

In this paper we have fabricated cylinder type micro channel using photoresist reflow and isotropic etching. Si substrate, using a Si/sub 3/N/sub 4/ (6000/spl Aring/) as a mask, was selectively etched using a HNA etching system for the bottom hemisphere of the channel. Photoresist reflow was used to make the top of the channel round. Then Si/sub 3/N/sub 4/ was deposited on the reflowed photoresist. Since the deposited Si/sub 3/N/sub 4/ was about 6000 /spl Aring/ thick it is possible to see the inside of the channel. This channel is expected to be applied to simple bio and microfluidic devices in which optical detection is needed.

Fabrications of a continuous-flow PCR-chip using dry film resist

In most miniaturized PCR-chip, the sample solution is introduced into a small chamber, and the DNA amplification is performed by thermal cycling. However, chamber heating and cooling rates are relatively low. But, the continuous-flow type PCR-chip involves the transfer of a PCR mixture through a micro-fluidic channel which passes through three different temperature regions. Therefore, it successfully addresses the problems of low heating and cooling rates. In this paper, a soda-lime glass substrate coated with a DFR of the fluid to cycle through different temperature zones was used to form a micro-channel structure and integrated Pt heater continuous-flow PCR.

A study on improving the surface morphology of recycled wafer forsolar cells using micro_blaster

Recently, recycling method of waste wafer has been an area of solar cell to cut costs. Micro_blasting is one of the promising candidates for recycling of waste wafer due to their extremely simple and cost-effective process. In this paper, we attempt to explore the effect of micro_blasting and DRE(damage removal etching) process for solar cell. The optimal process conditions of micro_blasting are as follows: sized powder, jetting pressure of 400 kPa, and scan_speed of 30 cm/s. And the particles formed on micro_blasted wafer were removed by DRE precess which was performed by using HNA(HF//) and TMAH(tetramethyl ammonium hydroxide). Structural analysis was done using a-step and the XRD patterns.

Fabrication of a micro-biochemical reactor with thick thermal isolation layer and integrated Pt heater/sensor in the micro-well

Recently many micro-biochemical reaction devices have been developed using MEMS technology because of the advantages of less required sample and reagent, fast reaction and less environmental contamination. The most important thing in biochemical reaction is temperature control. Unlike conventional micro-machined biochemical reactors which have an integrated heater and sensor at the backside of the wafer we have fabricated a thin Pt film heater and sensor on the bottom of the microwell at the frontside. In order to pattern inside the well, we used a thick negative Su-8 PR. As a desirable thermal isolation layer at the bottom of the well, we used a thick OPSL (oxidized porous silicon layer) formed by anodic reaction and multistep oxidation.

Enhancement of optical properties using bridge type electrodes for high efficiency photovoltaic cell

Recently, the important issues of photovoltaic cell are low cost and high efficiency. Making low cost and high efficiency photovoltaic cell, there are many effects to development of inexpensive wafer, simplify process and improve optical, electrical properties [1]. In this the study, the 2 step texturing method using micro blaster was developed to decrease reflection of incident lights. Bridge type electrode structures are suggested to expand the effective surface area and decrease the series resistance of finger electrode. We decided to use 10 µm size powders since efficiency of solar cell could rather reduce by using 50 µm size powders because of their extremely rough surface. And surface of after micro blaster etching with chemical etching method using HNA(HF: HNO3: CH3COOH = 4∶9∶7) solution, dry etching method using RIE, and oxide etching method removes oxide after wet oxidation process.