SIMULATION STUDY OF CONVEX CORNER UNDERCUTTING IN KOH AND TMAH FOR A MEMS PIEZORESISTIVE ACCELEROMETER

Undercutting is a common problem in wet anisotropic etching. This problem in turn, influences the performance and sensitivity of MEMS devices. This paper investigates the use of corner compensation to prevent convex corner undercutting in a MEMS piezoresistive accelerometer. The Intellisuite CAD simulation software was used for designing the mask with corner compensation and for analysing wet anisotropic etching profiles in potassium hydroxide (KOH) and tetra-methyl-ammonium-hydroxide (TMAH) solutions at different concentrations and temperatures. Perfect 90 degrees corners on the proof mass was successfully etched using a corner compensation design at etching temperature of 63 °C for KOH and 67.7 °C for TMAH with 25 wt% and 10.3 wt% concentration levels, respectively. Etching in TMAH required lower concentration level, thus making the etching process safer. However, TMAH required longer time to etch perfect convex corners compared to KOH. Nevertheless, both KOH and TMAH etchants have been successfully used to etch perfect convex corners by using the designed corner compensation mask.

SINTESIS DAN KARAKTERISASI PARTIKEL NANOSPERIK TIO2 MELALUI METODE HIDROTERMAL GELOMBANG MIKRO

ABSTRACTSimple synthesis of nanospherical TiO2 by microwave hydrothermal method has beeninvestigated. Titanium tetra isopropoxide (TTIP) and tetra methyl ammonium hydroxide(TMAOH) were used as precursor. The crystal phase and microstructure were characterized byX-Ray Diffraction (XRD) and transmission electron microscopy (TEM) including selected areadiffraction (SAED). The presence of intense peak in the XRD patterns confirmed to anatase andin good agreement with SAED patterns. Nanospherical of particles were clearly seen in theTEM image and the size of particles was approximately 4-5 nm.Keywords : microwave hydrothermal, colloidal titanates, structure directing agent,nanospherical TiO2

Experimental Study of Internal Forced Convection of Ferrofluid Flow in Porous Media

This work presents an experimental study of the effect of a magnetic field on laminar forced convection of a ferrofluid flowing in a tube filled with permeable material. The walls of the tube are subjected to a uniform heat flux and the permeable bed consists of uniform spheres of 3-mm diameter. The ferrofluid synthesis is based on reacting iron (II) and iron (III) in an aqueous ammonia solution to form magnetite, Fe3O4. The magnetite is mixed with aqueous tetra methyl ammonium hydroxide, (CH3)4NOH, solution. The dependency of the pressure drop on the volume fraction, and comparison of the pressure drop and the temperature distribution of the tube wall is studied. Also comparison of the wall temperature distribution, convection heat transfer coefficient and the Nusselt numbers of ferrofluids with different volume fractions is investigated for various Reynolds numbers (147 < Re < 205 ). It is observed that the heat transfer is enhanced by using a porous media, increasing the volume fraction had a similar effect. The pressure coefficient decreases for higher Reynolds number. The effect of magnetic field in four strategies, named modes, on ferrofluid flow through the porous media is presented.

Optimization of the Process Modules for a Top-Down Silicon Nanowire Fabrication Using Optical Lithography and Orientation Dependent Etching

A top-down silicon nanowire fabrication using a combination of optical lithography and orientation dependent etching has been developed using Silicon-on Insulator (SOI) as the starting substrate. The design of experiments for the optimization of the process flow especially on the orientation dependent etching using potassium hydroxide (KOH) and Tetra-Methyl Ammonium Hydroxide (TMAH) are presented in this paper. Based on the etching experiments using silicon substrates, KOH with added isopropyl alcohol (IPA) had shown to have a consistent etch rate with acceptable silicon surface roughness as compared with its other counterparts. The concern regarding the effect of line edge roughness (LER) as a result of optical lithography was highlighted and, therefore, the optimization of the patterning procedure was also discussed and presented.

Preparation of Large Size Pyramidal Texture on N-Type Monocrystalline Silicon Using TMAH Solution for Heterojunction Solar Cells

Pyramidal texture is one traditional method to realize antireflection for c-Si solar cells, due to its low cost and simplicity. As one high efficiency silicon solar cell, amorphous/crystalline silicon heterojunction (SHJ) solar cell has attracted much attention all over the world. The heterojunction interface with very low defects and interface states is critical to the SHJ solar cell performance. In order to obtain high quality interface passivation by depositing a very thin intrinsic amorphous silicon layer on the textured Si conformally, large size pyramidal texture with no metal ion contamination is required. In this work, we utilized tetra-methyl ammonium hydroxide (TMAH) instead of NaOH in the alkaline etching to prepare pyramidal texture on N-type monocrystalline silicon to avoid the possible Na+ contamination. By optimizing the etching conditions, uniform large size pyramidal texture with pyramid size of about 10 μm was fabricated successfully. Furthermore, excellent antireflection performance was demonstrated on such textured Si surface. The average reflectance was lower than 10% in the visible and near infrared spectrum range. Such pyramidally textured Si wafers will be very suitable for SHJ solar cells.

Al Bondpads, Halogens, and an ESCA-Based Search for the Invisible Cause of Poor Throughput at Wafer Probe

The authors use electron spectroscopy for chemical analysis and Auger electron analysis to study the interaction of Cl and F with Al thin-films deposited as thin-films on Si wafers and as Al bondpads. The motivation behind the study is F contamination being the putative source of poor throughput at wafer probe. F species stemming from NH4F and XeF2 exposure behave quite differently from HF on the Al surface. Whereas HF tends to attack the Al metal and leave an extended oxygenated-fluorinated surface, NH4F and XeF2 promote the formation of a stable, non-deliquescent fluoride salt of aluminum. HCl is far less corrosive to Al than HF, leaving a thin chlorinated-oxygenated surface. Immersion of Al thin-films in tetra-methyl-ammonium hydroxide (TMAH) and NH4OH provided non-halogenated surfaces for comparison. With exposure to air, the surface coated with the fluorinated Al salt (NH4F) adsorbs oxygen from the air to form a segregated AlF3/Al2O3 bilayer that remains stable with a total thickness on the order of 5 nm to 10 nm. Furthermore, wafers treated with NH4F display stellar throughput performance at wafer test despite having surface F contamination. A mechanical rather than chemical model is proposed to explain the improved performance at wafer probe with the immersion of wafers in a bath containing fluoride salts before wafer probe.

Evaluation of methanogenic treatment of TMAH (tetra-methyl ammonium hydroxide) in a full-scale TFT-LCD wastewater treatment process

This study evaluated TMAH biodegradation under methanogenic conditions. Under methanogenic conditions, a sludge from a full-scale UASB treating TFT-LCD wastewater was able to degrade 2,000 mg/L of TMAH within 10 h and attained a specific degradation rate of 19.2 mgTMAH/gVSS-h. Furthermore, several chemicals including some surfactants, DMSO, and sulfate were examined for their potential inhibitory effects on TMAH biodegradation under methanogenic conditions. The results indicated that surfactant S1 (up to 2%) and DMSO (up to 1,000 mg/L) presented negligible inhibitory effects on TMAH degradation, while surfactant S2 (0.2–1%) might inhibit methanogenic reaction without any TMAH degradation for 3–5 h. At sulfate concentrations higher than 300 mg/L, a complete inhibition of methanogenic reaction and TMAH biodegradation was observed. Results from cloning and sequencing of archaeal 16S rRNA gene fragments showed that Methanosarcina barkeri and Methanosarcina mazei were the dominant methanogens in the UASB treating TMAH-containing TFT-LCD wastewater.