Badariah Bais

Optimization of HNA etching parameters to produce high aspect ratio solid silicon microneedles

High aspect ratio solid silicon microneedles with a concave conic shape were fabricated. Hydrofluoric acid–nitric acid–acetic acid (HNA) etching parameters were characterized and optimized to produce microneedles that have long and narrow bodies with smooth surfaces, suitable for transdermal drug delivery applications. The etching parameters were characterized by varying the HNA composition, the optical masks window size, the etching temperature and bath agitation. An L9 orthogonal Taguchi experiment with three factors, each having three levels, was utilized to determine the optimal fabrication parameters. Isoetch contours for HNA composition with 0% and 10% acetic acid concentrations were presented and a high nitric acid region was identified to produce microneedles with smooth surfaces. It is observed that an increase in window size indiscriminately increases the etch rate in both the vertical and lateral directions, while an increase in etching temperature beyond 35 °C causes the etching to become rapid and uncontrollable. Bath agitation and sample placement could be manipulated to achieve a higher vertical etch rate compared to its lateral counterpart in order to construct high aspect ratio microneedles. The Taguchi experiment performed suggests that a HNA composition of 2:7:1 (HF:HNO3:CH3COOH), window size of 500 µm and agitation rate of 450 RPM are optimal. Solid silicon microneedles with an average height of 159.4 µm, an average base width of 110.9 µm, an aspect ratio of 1.44, and a tip angle and diameter of 19.2° and 0.38 µm respectively were successfully fabricated.

Design and analysis of MEMS piezoresistive SiO 2 cantilever-based sensor with stress concentration region for biosensing applications

This paper uses finite element method to obtain the optimal performance of piezoresistive microcantilever sensor by optimizing the geometrical dimension of both cantilever and piezoresistor. A 250 mum times 100 mum times 1 mum SiO2 cantilever integrated with 0.2 mum thick Si piezoresistor was used in this study. The sensor performance was measured on the basis of displacement sensitivity and surface stress sensitivity. The resulting maximum displacement value is about 0.7 nm for an applied load of 250 pN. A comparison between polySi and SiO2 cantilever has been carried out which shows the latter gives higher displacement for the same applied load. The sensor sensitivity was investigated by varying cantilever thickness as well as piezoresistor thickness. Simulation results show that the cantilever sensitivity is maximum when both the cantilever and the piezoresistor thicknesses are at minimum. Simulations were also conducted on the effects of incorporating various stress concentration region (SCR) designs at the bottom of the cantilevers. Cantilevers with incorporated stress concentration regions shows improved sensitivity over the cantilever without SCR. The cantilever with a rectangular shaped SCR extended up to the edge of the cantilever width yields a maximum Mises stress of 0.73 kPa compares to the other designs. For the same design, the cantilever with minimum SCR thickness of 0.2 mum yields maximum stress which results in maximum sensitivity.

The effects of temperature and KOH concentration on silicon etching rate and membrane surface roughness

The characterization of the KOH aqueous solution was done in order to study the effects of temperature and KOH concentration on the silicon etching rate for membrane formation. The study was done for temperatures ranging from 65/spl deg/C to 80/spl deg/C and KOH concentration ranging from 15% to 55%. Experiments showed that the temperature of 80/spl deg/C and KOH concentration of 35% will yield the optimum etching rate with the minimum surface roughness. A silicon membrane of thickness 48 /spl mu/m was produced with KOH concentration of 35% at the temperature of 75/spl deg/C for 7 hours and 45 minutes and the etching profile analyzed.

Characterization of HNA etchant for silicon microneedles array fabrication

Research on microneedles has been increasing rapidly to overcome the drawbacks of hypodermic needle which can results in painful injection, tissue damage and uncontrollable delivery rate. This paper presents process characterization of wet isotropic etching for solid microneedles array development. Work has been carried out to investigate the isotropic etching behavior in 17 different compositions of HNA solution. The experimental responses of vertical etch rate and lateral etch rate are presented. Resulting surface profiles from various HNA compositions are also reported. The etching properties will be applied to develop recipe to fabricate the optimum solid microneedles.

ZnAl2O4-Based Microwave Dielectric Ceramics as GPS Patch Antenna: A Review

This paper describes the potentials of zinc aluminate (ZnAl2O4) based microwave dielectric ceramics as patch antenna for GPS applications. Nowadays the GPS operating frequencies has been shifted from microwave technology to millimeter-wave technology. Various microwave dielectric ceramics (MDC) have been explored and widely used in telecommunication industries. Among the most interesting materials of that kind, zinc aluminate (ZnAl2O4) is recognized as one of the most promising non-metals and offers many advantages as GPS patch antenna. By modifying ZnAl2O4 compound with other materials, it is found to have high quality factor (Q>5,000), low dielectric constant (εr<20), and near zero temperature coefficient of resonant frequency (τf∼0). The studies also evidence the typical value of εr for GPS patch antenna and microwave substrate in the range of 4<εr<20 and 4<εr<10, respectively. The study also shows that the ZnAl2O4-based MDC can be successfully fabricated as microstrip patch antenna, which meets the requirements of GPS application.

Suspension design analysis on the performance of MEMS area-changed lateral capacitive accelerometer

In this paper, variations of folded beam suspension design are analyzed and simulated in order to study its effect on the performance of an area-changed MEMS lateral capacitive accelerometer. The simulation was carried out using Coventorware2003. Mechanical issues like spring constants, stress distributions, cross-axis sensitivities and shock survivability are discussed.

Hybrid Simulation Approach on MEMS Piezoresistive Microcantilever Sensor for Biosensing Applications

This paper uses a hybrid simulation approach in CoventorWare design environment which combines finite element analysis and circuit simulation modeling to obtain the optimal performance of piezoresistive microcantilever sensor. A 250 μm x 100 μm x 1 μm SiO2 cantilever integrated with 0.2 μm thick Si piezoresistor were used in this study. A finite element analysis on piezoresistive microcantilever sensor was conducted in CoventorWare Analyzer environment which incorporates MemMech and MemPZR modules. The sensor sensitivity was obtained by measuring resistivity changes in piezoresistive material in response to surface stress changes of microcantilever. The simulation results were later integrated with system-level simulation solver called Architect to enable the optimization of the sensor circuit output. It involves a hybrid approach which uniquely combined FEM analysis and piezoresistive modeling using circuit simulation environment which results in optimal performance of MEMS piezoresistive microcantilever sensor.

Structure Design and Fabrication of an Area-changed Bulk Micromachined Capacitive Accelerometer

In this paper, a lateral capacitive MEMS accelerometer for low-g applications was designed and fabricated. The accelerometer is chosen to be based on an area-changed detection scheme. Area-changed accelerometers can provide alternatives in designing high sensitivity and low mechanical noise floor sensors as it is capable of providing a large proof mass. Based on the calculation of sensitivity and basic resonance frequency, three kinds of accelerometers were designed and optimized. Bulk silicon is chosen as the proof mass material and a three-mask micromachining technology was adopted to fabricate the active structures of the accelerometer. Deep RIE and wafer bonding techniques are utilized as it offers solutions in fabricating the thick proof mass and high aspect ratio sensing element structures with small sensing gaps to achieve high sensitivity and low noise performance.

Microfabrication of Si3N4-polyimide membrane for thermo-pneumatic actuator

Purpose – The purpose of this paper is to discuss the fabrication technology and test of thermo-pneumatic actuator utilizing Si3N4-polyimide thin film membrane. Thin film polyimide membrane capped with Si3N4 thin layer is used as actuator membrane which is able to deform through thermal forces inside an isolated chamber. The fabricated membrane will be suitable for thermo-pneumatic-based membrane actuation for lab-on-chip application. Design/methodology/approach – The actuator device consisting of a micro-heater, a Si-based micro-chamber and a heat-sensitive square-shaped membrane is fabricated using surface and bulk-micromachining process, with an additional adhesive bonding process. The polyimide membrane is capped with a thin silicon nitride layer that is fabricated by using etch stop technique and spin coating. Findings – The deformation property of the membrane depend on the volumetric expansion of air particles in the heat chamber as a result of temperature increase generated from the micro-heater i...

Synthesization of nickel nanoparticles embedded in SU8 polymer for electromagnetic actuator membrane

A study of synthesization and magnetic properties of cured polymer composite on nickel (Ni) as an actuator membrane is prepared in this work. SU8 3050 polymer is used to mix with magnetic nanoparticles Ni to produce a hybrid material. The mixing process are done by using mechanical stirrer, ultrasonication and manually hand stirring. In this work an easy sol-gel method is selected to embed magnetic particles into the polymer matrix. Characterization of particle distribution is observed by metallurgical microscopy and scanning electron microscope (SEM). It is observed that the spreading of Ni particles inside the polymer chain are constant without clustering effects. Magnetization curves of each sample are traced at room temperature using vibration sample magnetometer (VSM). A good compromising magnetic properties with patternable high aspect ratio structures have been successfully fabricated using a standard MEMS process.