Azrul Azlan Hamzah

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.

HF Etching of Sacrificial Spin-on Glass in Straight and Junctioned Microchannels for MEMS Microstructure Release

Sacrificial spin-on glass (SOG) etching in straight and junctioned microchannels using hydrofluoric acid (HF) was investigated. SOG etch rates in both reaction-dominant and diffusion-dominant regimes for various HF concentrations were studied. An etching model based on a non-first-order chemical reaction/steady-state diffusion etching mechanism is presented to compensate for the etching effect at the channel junction. Straight microchannels 1500 μm in length and various widths were fabricated on silicon substrate by coating a hardened photoresist layer over rectangular-shaped SOG layers. Junctioned microchannels were fabricated on silicon by filling SOG into deep reactive ion etching (DRIE)-etched microchannels. The samples were time-etched in HF solution and etch-front propagation was observed under an optical microscope. It is observed that the SOG etch rate is linear in the reaction-limited region and drops approximately 70% in the diffusion-limited region. The SOG etch rate in microchannels is independent of channel width and depth. The SOG etch rate at the T-junction is 0.67 times lower than its etch rate in straight channels due to the instantaneous drop in HF concentration. This behavior is well embodied by the presented numerical model. Finally, 5% HF is suitable for release etch due to its acceptable etch rate while being less damaging to microelectromechanical system (MEMS) microstructures.

Deflection analysis of epitaxially deposited polysilicon encapsulation for MEMS devices

Numerical and simulation studies are done to determine deflection behavior of epitaxially deposited polysilicon encapsulation. Polysilicon encapsulation, which is used as physical protection for moving parts of MEMS devices, is applied with external pressure to replicate packaging processes. Polysilicon encapsulations thickness 10, 20, 30, and 40 micron with seal oxide of thickness 2, 4, 6, 8, and 10 micron are analyzed. Ritzs and energy methods are used to numerically approximate surface deflection of polysilicon encapsulation when perpendicularly loaded with a uniform pressure varying from 10 to 100 atm. Simulation was done using CoventorWare ver.2001.3 software. It is observed that numerical analysis values approximate theoretical values for small deflection (W >t). Thus, numerical analysis could be use to predict deflection behavior of encapsulation in that region.

A tapered aluminium microelectrode array for improvement of dielectrophoresis-based particle manipulation.

In this work, the dielectrophoretic force (FDEP) response of Aluminium Microelectrode Arrays with tapered profile is investigated through experimental measurements and numerical simulations. A standard CMOS processing technique with a step for the formation of a tapered profile resist is implemented in the fabrication of Tapered Aluminium Microelectrode Arrays (TAMA). The FDEP is investigated through analysis of the Clausius-Mossotti factor (CMF) and cross-over frequency (fxo). The performance of TAMA with various side wall angles is compared to that of microelectrodes with a straight cut sidewall profile over a wide range of frequencies through FEM numerical simulations. Additionally, electric field measurement (EFM) is performed through scanning probe microscopy (SPM) in order to obtain the region of force focus in both platforms. Results showed that the tapered profile microelectrodes with angles between 60° and 70° produce the highest electric field gradient on the particles. Also, the region of the strongest electric field in TAMA is located at the bottom and top edge of microelectrode while the strongest electric field in microelectrodes with straight cut profile is found at the top corner of the microelectrode. The latter property of microelectrodes improves the probability of capturing/repelling the particles at the microelectrode’s side wall.

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.

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.

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.

Finite element modeling of dielectrophoretic microelectrodes based on a array and ratchet type

This research describes an investigation of nonuniform electric field for dielectrophoretic forces (FDEP) application in particles and cells manipulation. In an electro kinetics occurrence, a miniaturized array and ratchet type microelectrodes has been simulated. The study of optimal FDEP behavior on the electric field distribution for both type microelectrodes was characterized and optimized by finite element method, (FEM). A set of array and ratchet type microelectrode are biased to generate asymmetric electric field distribution. Normalization of microelectrode simulation result shows that array and ratchet type produced a comparable electric field strength and direction. Deployment of additional dimension for array type electrode, three poles produced the highest of electric field strength of 7.513 e7 V/m and displacement field direction of 2.758 e-3 C/m2. Simulation results are used to design a higher sensitive and selective of a dielectrophoretic (DEP) microelectrode for selection, collection and processing of particle and cell using optimal FDEP that determination advancement in the development of dielectrophoretic a lab-on-a-chip. Ultimately, the findings of this work is possible to contribute in medical sciences research for the enrichment of stem cell from bone narrow and peripheral blood form via integration DEP into a lab on a chip, (DLOC) concept application.

Dielectrophoretic characterization of array type microelectrodes

This research describes an investigation of nonuniform electric field for dielectrophoretic forces, FDEP application in particles manipulation. In an electrokinetics occurrence, a miniaturized array type of two poles microelectrodes has been simulated using engineered particle and tested using graphite metalloid particles. The particles can be attracted towards the regions of strong electric field depending upon the particles is more polarisable than the suspending medium. Dielectrophoresis offers the controllable, selective and accurate manipulation of target graphite metalloid particles. The surface area of graphite attracted to microelectrodes gradually increased starting from 4 seconds for 3412, 3845, and 3764 um2, hence 4589, 4465 and 4739 um2 at the 6 seconds mark and finally 5588, 5569 and 5644 um2 after 8 seconds for three different test run respectively. Further study of optimal FDEP behavior on the electric field distribution for three poles microelectrodes was characterized by finite element method, (FEM). The outcome, FDEP response is further improved by additional poles microelectrodes from top side, instead of side by side in term the strength and direction of electric and displacement field. Ultimately, the findings of this work is possible to contribute in medical sciences research for the enrichment of stem cell from bone narrow and peripheral blood form via integration DEP into a lab on a chip, DLOC concept application.

Finite element analysis on magnetic force generation of electromagnetic microactuator for micropump

In this work, a theoretical analysis on the magnetic force generation of micro-actuator driven by planar microcoil is reported. The actuator design is optimized to increase the magnetic force and flux density that is useful for mechanical membrane deformation of an actuator. Therefore, this work is focused on the design and simulation of actuator material and structure using a finite element analysis method. As the results, the obtained magnetic force of maximum 11.4 mN has been observed for the actuator design having coil geometry of width w = 100 μm, space s =100 μm, turn N = 20 and thickness t =20 μm with NdFeB as magnet material. Hence, the optimized design geometry of the coil can be used as reference for the fabrication of electromagnetic actuator for micropump application.