Jumril Yunas

Exploring the Innovational Potential of Biomimetics for Novel 3D MEMS

A novel way to describe the complexity of biological and engineering approaches depending on the number of different base materials is proposed: Either many materials are used (material dominates) or few materials (form dominates) or just one material (structure dominates). The complexity of the approach (in biology as well as in engineering) increases with decreasing number of base materials. Biomimetics, i.e., technology transfer from biology to engineering, is especially promising in MEMS development because of the material constraints in both fields. The Biomimicry Innovation Method is applied here for the first time to identify naturally nanostructured rigid functional materials, and subsequently analyse their prospect in terms of inspiring MEMS development.

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 Fabrication of MEMS Micropumps using Double Sided Etching

In this paper, we report a simple technique for the fabrication of planar valveless micropumps. The technique utilizes MEMS fabrication methods by using a double sided etch technique. Instead of using several masks and process steps, an anisotropic wet etch technique at both sides of a silicon substrate is implemented at the same time for creating the pump membrane and the diffuser/nozzle elements. A planar diffuser and a nozzle element of the pump, as well as a 150 μm thick silicon membrane, are designed and fabricated using only three pattern process steps. An actuator-chamber and a pump-chamber with depths of 250 μm are formed after 250 min KOH etching, while the diffuser/nozzle element with a depth of 50 μm are sequentially formed after chamber forming. The process is simple and reproducible which opens the opportunity for fast prototyping of MEMS micropumps.

Electrochemically deposited and etched membranes with precisely sized micropores for biological fluids microfiltration

This paper presents simple and economical, yet reliable techniques to fabricate a micro-fluidic filter for MEMS lab-on-chip (LoC) applications. The microporous filter is a crucial component in a MEMS LoC system. Microsized components and contaminants in biological fluids are selectively filtered using copper and silicon membranes with precisely controlled microsized pores. Two techniques were explored in microporous membrane fabrication, namely copper electroplating and electrochemical etching (ECE) of silicon. In the first technique, a copper membrane with evenly distributed micropores was fabricated by electroplating the copper layer on the silicon nitride membrane, which was later removed to leave the freestanding microporous membrane structure. The second approach involves the thinning of bulk silicon down to a few micrometers thick using KOH and etching the resulting silicon membrane in 5% HF by ECE to create micropores. Upon testing with nanoparticles of various sizes, it was observed that electroplated copper membrane passes nanoparticles up to 200?nm wide, while porous silicon membrane passes nanoparticles up to 380?nm in size. Due to process compatibility, simplicity, and low-cost fabrication, electroplated copper and porous silicon membranes enable synchronized microfilter fabrication and integration into the MEMS LoC system.

Comparative study of stack interwinding micro-transformers on silicon monolithic

Interwinding planar micro-transformers are developed using micro-machining technique. The transformers with a vertically stack coil structure on silicon monolithic substrate are designed to achieve high coupling and high inductance value in a relatively small coil area. In this work, various types of stack interwinding transformer are fabricated, measured and compared. The results show that the metal-to-metal effect of a multi-layer structure contributes to the significant increase of parasitic capacitances and hence limits the operating frequency. Moreover, the lumped element parameters are analyzed by extracting the measured S-parameter. This investigation can give important information for the future development of three-dimensional RF devices.

Low cost fabrication of microfluidic microchannels for Lab-On-a-Chip applications

Microfluidic systems are one of the new growing technologies which offer miniaturization of analysis systems. In this paper we present a simple and low cost fabrication of microchannels using in different applications in Micro Total Analysis Systems. This method uses typical microscopic glass slides as a substrate for fabrication of microchannels. Using photo-resist as a mask instead of some deposition methods makes the procedure more convenient and cost effective compare to other techniques. A smooth channel surface with acceptable sharp wall edges makes this procedure suitable for so many applications that vertical walls are not crucial. The comparison between fabrication of channels using wet etching procedures and molding techniques can help to select the more suitable one for any application which needs specific characteristics.

Superparamagnetic calcium ferrite nanoparticles synthesized using a simple sol-gel method for targeted drug delivery

The calcium ferrite nano-particles (CaFe2O4 NPs) were synthesized using a sol-gel method for targeted drug delivery application. The proposed nano-particles were initially prepared by mixing calcium and iron nitrates that were added with citric acid in order to prevent agglomeration and subsequently calcined at a temperature of 550°C to obtain small particle size. The prepared nanoparticles were characterized by using an XRD (X-ray diffraction), which revealed the configuration of orthorhombic structures of the CaFe2O4 nano-particles. A crystallite size of ~13.59 nm was obtained using a Scherers formula. Magnetic analysis using a VSM (Vibrating Sample Magnetometer analysis), revealed that the synthesized particles exhibited super-paramagnetic behavior having magnetization saturation of approximately 88.3emu/g. Detailed observation via the scanning electron microscopy (SEM) showed the calcium ferrite nano-particles were spherical in shape.

On the Way to the Bionic Man: A Novel Approach to MEMS Based on Biological Sensory Systems

The human senses are of extraordinary value, but we cannot change them, even if this proves to be a disadvantage in our modern times. However, we can assist, enhance and expand these senses via MEMS. This paper introduces data for a push-pull analysis method based on a concise summary of senses in organisms and MEMS sensors that already have reached the market, giving an overview where current MEMS technology excels (available solutions) and where natural sensor systems excel. It provides a knowledge base for further development of MEMS sensors. Some animals and even humans (with artificial lenses after cataract surgery) can see in the infrared and ultraviolet range; related MEMS with IR/UV sensitivity might assist us to determine the status of organisms. The hearing capabilities of bats (ultrasound) can inspire echolocation in man. Butterflies have exquisite thermoregulation; this might lead to MEMS that are better protected from overheating. Mice can smell important information about another mouse’s immune system and mosquitoes detect minuscule amounts of carbon dioxide and lactic acid; thereby inspired MEMS could serve as medical or environmental scanners. The senses for magnetism, vibrations and electroreception that are used by animals might satisfy the need for MEMS in navigation and orientation. MEMS that are skillfully added to the human body can provide additional perceptory data. Future research will identify where already available MEMS excel and which outstanding properties of sensory systems can easily be replicated by ‘off the shelf’ systems.

Piezoeletric Micropump for Drug Delivery System Fabricated Using Two Optical Masks

. In this study, a Piezoelectric Actuated Valveless Micropump (PAVM) has been designed and successfully fabricated using MEMS fabrication processes. A PZT: Pb (ZrTi) Ox (lead titanate zirconate) disc is used to actuate a silicon membrane by applying an alternating electrical field across the actuator. The resultant reciprocating movement of the pump membrane is then converted into pumping effect. Preliminary analysis of the fluidic characteristics of this micropump was performed using CoventorWare Simulator with MEMs-FSI (Fluid Structure Interaction) module to understand the working behaviour of the pump system. The pump is fabricated in a simple micromachining process with two optical masks using a double side polished silicon wafer. The tests carried out on the micropump have produced promising results to be used in the drug delivery system.

Sputtered Encapsulation as Wafer Level Packaging for Isolatable MEMS Devices: A Technique Demonstrated on a Capacitive Accelerometer

This paper discusses sputtered silicon encapsulation as a wafer level packaging approach for isolatable MEMS devices. Devices such as accelerometers, RF switches, inductors, and filters that do not require interaction with the surroundings to function, could thus be fully encapsulated at the wafer level after fabrication. A MEMSTech 50g capacitive accelerometer was used to demonstrate a sputtered encapsulation technique. Encapsulation with a very uniform surface profile was achieved using spin-on glass (SOG) as a sacrificial layer, SU-8 as base layer, RF sputtered silicon as main structural layer, eutectic gold-silicon as seal layer, and liquid crystal polymer (LCP) as outer encapsulant layer. SEM inspection and capacitance test indicated that the movable elements were released after encapsulation. Nanoindentation test confirmed that the encapsulated device is sufficiently robust to withstand a transfer molding process. Thus, an encapsulation technique that is robust, CMOS compatible, and economical has been successfully developed for packaging isolatable MEMS devices at the wafer level.