Noraini Marsi

The Mechanical and Electrical Effects of MEMS Capacitive Pressure Sensor Based 3C-SiC for Extreme Temperature

This paper discusses the mechanical and electrical effects on 3C-SiC and Si thin film as a diaphragm for MEMS capacitive pressure sensor operating for extreme temperature which is 1000 K. This work compares the design of a diaphragm based MEMS capacitive pressure sensor employing 3C-SiC and Si thin films. A 3C-SiC diaphragm was bonded with a thickness of 380 μm Si substrate, and a cavity gap of 2.2 μm is formed between the wafers. The MEMS capacitive pressure sensor designs were simulated using COMSOL ver 4.3 software to compare the diaphragm deflection, capacitive performance analysis, von Mises stress, and total electrical energy performance. Both materials are designed with the same layout dimensional with different thicknesses of the diaphragm which are 1.0 μm, 1.6 μm, and 2.2 μm. It is observed that the 3C-SiC thin film is far superior materials to Si thin film mechanically in withstanding higher applied pressures and temperatures. For 3C-SiC and Si, the maximum von Mises stress achieved is 148.32 MPa and 125.48 MPa corresponding to capacitance value which is 1.93 pF and 1.22 pF, respectively. In terms of electrical performance, the maximum output capacitance of 1.93 pF is obtained with less total energy of 5.87 × 10−13 J, thus having a 50% saving as compared to Si.

Biopolymer doped with titanium dioxide superhydrophobic photocatalysis as self-clean coating for lightweight composite

The development of a lightweight composite (LC) based on Portland cement concrete with waste lightweight aggregate (WLA) additive was carried out to improve the sustainability and environmental impact and to offer potential cost savings without sacrificing strength. Treatment of the surface of the LC exposed to environmental attack by coating with biopolymer based on waste cooking oil doped with titanium dioxide photocatalysis (TOP) with superhydrophilic property was found to affect the mechanical properties of the LC in a systematic way. The results of compressive strength showed that the composite achieved the minimum required strength for lightweight construction materials of 17.2 MPa. Scratch resistance measurements showed that the highest percentages loading of superhydrophilic particles (up to 2.5% of biomonomer weight) for LCs surface coating gave the highest scratch resistance while the uncoated sample showed the least resistances. Scanning electron microscope (SEM) pictures revealed the difference between the surface roughness for LC with and without TOP coating. TOP is also formulated to provide self-cleaning LC surfaces based on two principal ways: (1) the development by coating the LC with a photocatalytic superhydrophilic, (2) if such a superhydrophilic is illuminated by light, the grease, dirt, and organic contaminants will be decomposed and can easily be swept away by rain.

Characterization of ProTEX® PSB Thin Film as a Photosensitive Layer for MEMS Capacitive Pressure Sensor Diaphragm Based on SiC-on-Si Wafer

The ProTEX® PSB thin film as a photosensitive layer has been released in the market as an alternative replacement for silicon nitride or silicon oxide wet etch masks. In this work, this film has been deposited on SiC-on-Si wafer for the back-etching of the bulk Si to leave SiC thin film to be used as a pressure sensor diaphragm. This paper will discuss the process flow to estimate the optimized ProTEX® PSB thin film thickness for the sufficient back-etching of the 300um bulk Si. This thickness is defined by the following parameters: spin-coating rotational speed, final cure temperature and hard bake time of coating. Several samples of ProTEX® PSB thin films have been preliminary characterized by infinite focus microscopy (IFM) and scanning electron microscopy (SEM) to examine the substrate surface conditions and the effects of undercut edges structure. Based on these data, it was determined that the optimum thickness of ProTEX® PSB for this project is 2.133 μm with the spin speed of 3000 rpm, the first bake temperature of 110 °C in 120 seconds and the second bake temperature of 240 °C in 60 seconds. We conclude that ProTEX® PSB can withstand the etch mask with etch rate of 1.28 μm/min for 8 hours and gives good quality effect of undercut edge on the SiC-on-Si wafer.

The Capacitance and Temperature Effects of the SiC- and Si-Based MEMS Pressure Sensor

This project develops the pressure sensor for monitoring the extreme conditions inside the gas turbine engine. The capacitive-based instead of piezoresistive-based pressure sensor is employed to avoid temperature drift. The deflecting (top) plate and the fixed (bottom) plate generate the capacitance, which is proportional to the applied input pressure and temperature. Two thin film materials of four different sizes are employed for the top plate, namely cubic silicon carbide (3C-SiC) and silicon (Si). Their performances in term of the sensitivity and linearity of the capacitance versus pressure are simulated at the temperature of 27°C, 500°C, 700°C and 1000°C. The results show that both materials display linear characteristics for temperature up to 500°C, although SiC-based sensor shows higher sensitivity. However, when the temperatures are increased to 700°C and 1000°C, the Si- based pressure sensor starts to malfunction at 50 MPa. However, the SiC-based pressure sensor continues to demonstrate high sensitivity and linearity at such high temperature and pressure. This paper validates the need of employing silicon carbide instead of silicon for sensing of extreme environments.

Electrical performances based on two different structured of micro supercapacitor electrodes

This paper discusses electrical performances of the micro supercapacitor such as cyclic voltammetry and charge discharge between two different structure of electrodes. The microsupercapacitor was constructed of Polypyrrole (Ppy) coated nickel electrode as current collector and polyvinyl alcohol (PVA) as solid state electrolyte. The electrochemical performances of the microsupercapacitor such as cyclic voltammetry also typically known as I-V curve and a typical time based charge discharge curve were investigated with different structured of electrode which is interdigital electrode and planar electrode for the same layout. In Comsol Multiphysics ver. 4.2a, the Secondary Current Distribution and Transport of Diluted Species has been selected as the Application module. I-V curve for the micro supercapacitor with the two structured of electrodes was simulated. The transport of a reduced and an oxidized species is described by time-dependent mass transfer principles for diffusion under dilute conditions. The maximum current response for the interdigital electrode is 5.5 A/m and for the planar electrode is 0.025 A/m. For the interdigital electrode, the maximum voltan achieved at 0.5 V same for the planar electrode with different time. Discharging process for interdigital and planar electrode occurred when the value of voltage decreasing and back to zero at 1s and 10 s respectively.

Design and simulation of piezoelectric micro power harvester for capturing acoustic vibrations

Piezoelectric Micro-Power Harvester (PMPH), harvests mechanical vibration sources available in the environment and converts it to usable electric power via piezoelectric effects. The low power requirements and small device dimensions enable PMPH to supply enough power necessary to a variety of applications such as wireless sensor nodes, wrist watches and cell phone signals, thus proving to be an excellent alternative source for traditional lithium iodide battery especially in body sensor nodes. In this paper we design PMPH that is able to harvest environmental vibration sounds and convert it to usable electrical power for artificial cochlea. Spring mass damper system with single degree of freedom is used to model PMPH. COMSOL Multiphysics 4.2 is used to simulate PMPH. a linear relationship between voltage and external load for piezoelectric materials during Static analysis is observed, Eigenfrequency is used to find the resonance frequencies for six modes of operation and its deflection shape, PMPH harvest the maximum acoustic vibration at first mode of operation at 589 Hz. Simulation results using Transient analysis show that PMPH total displacement about 6 μm and output voltage at center of piezoelectric material about 4*10-15Vp-p at steady state and can harvest acoustic vibration at 598Hz and convert it to electric power about 23nW, which is sufficient for cochlear implant application.

Development of a silicon carbide MEMS capacitive pressure sensor operating at 500 °C

In this paper, we present development of MEMS capacitive pressure sensor based silicon carbide (3C-SiC) materials. The sensor is made up of four elements: a 3C-SiC diaphragm, silicon substrate, a reliable stainless steel (SS) o-ring and (SS) vacuum clamper as the package. The designed are inherent simplicity and ruggedness of this physical configuration that acceptably performed for extreme environment applications such as in gas turbine engine. This study reported a reliability testing of a prototype package MEMS capacitive pressure sensor verified up to 500 °C through high temperature lab testing. At 500 °C, the reliability test results show that the sensitivity of 0.826 pF/MPa is achieved. Experimentally, sensor nonlinearity of 0.61 % is found with hysteresis of 3.13 %. The maximum temperature coefficient of output change is 0.073 %/°C measured at 5 MPa.

Characterization direct bonding of SiC/SiN layer on Si wafer for MEMS capacitive pressure sensor

Two silicon wafer size of 2.5 mm × 2.5 mm with 1 μm LPCVD silicon carbide (SiC) and 200 nm LPCVD silicon nitride, respectively has been characterize direct bonding between silicon nitride and silicon carbide surfaces. Chemical-mechanical polishing (CMP) treatment processes were performed to reduce the surface roughness of both surfaces before the surface are bonded to each other. The surface roughness shows about 1 μm before CMP treatment, while the smoothness of the surface roughness values as low as 20 nm was obtained after CMP treatment as measured by infinite focus microscopy (IFM). The interface between SiC/SiN layers on Si wafer was inspected by scanning electron microscopy (SEM). Heat treatment with different annealing temperatures is indentified that an optimized annealing process was at 400 °C for 2 hours to allow the bond-forming interface between silicon nitride and silicon carbide surfaces being bonded at 8.3467 MPa.

The Synthesis and Surface Properties of Newly Eco-Resin Based Coconut Oil for Superhydrophobic Coating

The paper presents the synthesis of newly eco-resin based on coconut oil for superhydrophobic coating. Superhydrophobicity of the coating provide a self-cleaning or water-repellent characteristic that prevents peeling, thereby extend the life expectancy of the coating. The use of newly synthesized eco-resin offer a sustainable, eco-friendly and cost effective source of nature. The synthesis and formulation of different percentages of coconut oil which is 20, 40, 60 and 80 weight by weight percentage (wt/wt%) consists of three phases to form superhydrophobic coating. The first phase involved alcoholysis step, condensation step and third phase purification through alcoholysis. The adhesion test (ASTM D3359-03) results was obtained the highest classification grading of 5B for coating at 80% (wt/wt) of coconut oil with 9 layer whereas the rate of adhesion is 9.87% of the area affected. It is shows that the small flakes of coating are detached at intersections. Scratch resistance test was evaluated in terms of pencil hardness grade, which is increased from grade HB to 6H and there is minor scratch occurs for 9 layer coating. The water droplet test was demonstrated that the advancing water contact angle up to 60% of coconut oil at 169.22o with the smooth surface roughness at 0.2448 μm.

The Effects of Biopolymers Composite Based Waste Cooking Oil and Titanium Dioxide Fillers as Superhydrophobic Coatings.

This project presents the effect of biopolymer composite surface coating on TiO2 fillers by analysing the static water contact angle, SEM micrographs, porosity, density and refractive index of biopolymer doped with different loading of TiO2. The different ratio loading of 0.5, 1.0, 1.5, 2.0 and 2.5 (wt/wt%) TiO2 can be used to improve the material properties in practical use for outdoor application especially to enhance the stability of surface coating. It is found that the smooth surfaces with a low ratio loading of TiO2 fillers on biopolymer composite surface coating increases the static water contact angle up to 162.29°. It is interpreted with respect to nano- features existing on the surface of the water repellent creates a thin superhydrphobic layer. The relationship between porosity and density is indirectly proportional where the higher the loading of TiO2 filler produce the lower porosity up to 0.86% of the surface coating. The movement from shorter to longer of wavelength was observed before and after exposure indicates that there are optimization of absorption of UV-B radiation as the amount of delocalisation.