Over the last few years a number of sensing platforms are being investigated for their use in drug development, microanalysis or medical diagnosis. Lab-on-a-chip (LOC) are devices integrating more than one laboratory functions on a single device chip of a very small size, and typically consist of two main components: microfluidic handling systems and sensors. The physical mechanisms that are generally used for microfluidics and sensors are different, hence making the integration of these components difficult and costly. In this work we present a lab-on-a-chip system based on surface acoustic waves (for fluid manipulation) and film bulk acoustic resonators (for sensing). Coupling surface acoustic waves into liquids induces acoustic streaming and motion of micro-droplets, whilst it is well-known that bulk acoustic waves can be used to fabricate microgravimetric sensors. Both technologies offer exceptional sensitivity and can be fabricated from piezoelectric thin films deposited on Si substrates, reducing the fabrication time/cost of the LOC devices.
This paper describes a MEMS (micro-electromechanical systems) modulator suitable for optical system network
signaling. Several actuator mechanisms exist that potentially satisfied this purpose, electrostatic actuation was identified
as the most suitable for the application due to speed of operation and low power consumption. MEMS geometry and
analytical mode models were developed and applications performance estimated including multiphysics phenomena.
Finite element analysis was undertaken using the commercially available software suite, COMSOL(R), performing static
and dynamic simulations and analyses in the time and frequency domains. The proposal is that the MEMS modulator
would be integrated with other optical components encased in a hermetically sealed vacuum environment, resulting in a
lightly damped response with decaying oscillation. A two-step drive signal was developed and simulated using the multidomain,
simulation package SIMULINK®. The optimized MEMS design and two-step driver realized a MEMS optical
modulator meeting the required specification. Finally a proposal for integration within an optical transmitter assembly is
Metal based thermal microactuators normally have lower operation temperatures than those of Si-based ones; hence they have great potential for applications. However, metal-based thermal actuators easily suffer from degradation such as plastic deformation. In this study, planar thermal actuators were made by a single mask
process using electroplated nickel as the active material, and their thermal degradation has been studied. Electrical tests show that the Ni-based thermal actuators deliver a maximum displacement of ~20 m at an average temperature of ~420 °C, much lower than that of Si-based microactuators. However, the displacement strongly depends on the frequency and peak voltage of the pulse applied. Back bending was clearly observed at a maximum temperature as low as 240 °C. Both forward and backward displacements increase with increasing the
temperature up to ~450 °C, and then decreases with power. Scanning electron microscopy observation clearly showed that Ni structure deforms and reflows at power above 50mW. The compressive stress is believed to be responsible for Ni piling-up (creep), while the tensile stress upon removing the pulse current is responsible for
necking at the hottest section of the device. Energy dispersive X-ray diffraction analysis revealed severe oxidation of the Ni-structure induced by Joule-heating of the current.
A TiNi/diamond-like-carbon (DLC) microcage for biological application has been designed, fabricated and
characterized. A compressively stressed DLC film with TiNi pattern on top lifts the fingers upwards once they are
released from the substrate, and the microcage can be closed through shape memory effect of top TiNi film with
temperature below 80°C. Further heating above 100°C, the gradual opening of the microcage can be obtained due to
thermal bimorph effect. The biocompatibility of both the TiNi and DLC films has been proved using a cell-culture
This paper compared the three different methods for determination of thin film modulus or MEMS applications: 1) scanning bending cantilever, 2) nanoindentation and 3) resonance frequency method. Surface profilometer was used to scan along the micro-machined cantilevers at different loads and produce the bending profile, from which the Youngss modulus can be extracted. Indentation profiled produced by Nano-indenter can deduce Young's modulus and hardness of the thin film materials. AFM vibrometer is used to detect the resonance of the thin film cantilever, from which the stiffness, and therefore the Young's modulus can be derived. The material properties of silicon nitride characterized by three methods are consistent and comparable with one another. The following MEMS materials: SiN, Ni, Ni/SiN bimorph, Nano-Diamond, SiC have been characterized and compared by using different method. Their advantages and disadvantages are also discussed.
A number of in-plane spring-like micro-electro-thermal-actuators with large displacements were proposed. The devices take the advantage of the large difference in the thermal expansion coefficients between the conductive arms and the insulator clamping beams. The constraint beams in one type (the spring) of these devices are horizontally positioned to restrict the expansion of the active arms in the x-direction, and to produce a displacement in the y-direction only. In other two types of actuators (the deflector and the contractor), the constraint beams are positioned parallel to the active arms. When the constraint beams are on the inside of the active arms, the actuator produces an outward deflection in the y-direction. When they are on the outside of the active arms, the actuator produces an inward contraction. Analytical model and finite element analysis were used to simulate the performances. It showed that at a constant temperature, analytical model is sufficient to predict the displacement of these devices. The displacements are all proportional to the temperature and the number of the chevron sections. A two-mask process is under development to fabricate these devices, using Si3N4 as the insulator beams, and electroplated Ni as the conductive beams.
Mechanical characterization is vital for the design of MEMS/NEMS. Many methods have been developed to measure the mechanical properties of materials; however, most of them are either too complicated, or expensive for industrial application, or not accurate. This paper describes a new characterization method to extract the mechanical properties of the materials that is simple, inexpensive and applicable to a wide range of materials. The beams of the material under tests, are patterned by laser micromachining and released by KOH etch. Surface profilometer is used to scan along μ-machined cantilevers and produce a bending profile, from which the Young’s modulus can be extracted. The errors due to initial curling and anticlastic (width) effect have been carefully studied. A new ANSYS FEA model is developed to evaluate the effects and test structure designs. SiNx, Ni, SiC and nanocrystal diamond cantilevers have been fabricated and their mechanical properties, e.g. Young’s modulus have been evaluated as 154+/-12GPa, 202+/-16GPa, 360+/-50GPa and 504+/-50GPa, respectively. These results are consistent with those measured by nano-indentation. Residual stress gradient has also been extracted by surface profilometer, which is comparable with the results inferred from Zygo interferometer measurements. It is also possible to extract plate modulus and Poisson ratio with minimal error achieved. This method can be extended to AFM or nanometer-stylus profilometer for NEMS mechanical characterization.
Three types of micropumps based on TiNi shape memory alloy thin films were designed and fabricated. The TiNi films were prepared on silicon substrate by co-sputtering TiNi target and a separate Ti target at room temperature, and then post annealed at 650°C. The first pump design is based on a single TiNi/Si bimorph membrane structure with inlet and outlet. The second design is based on three layer structures bonded together, with one TiNi/Si active membrane structure and two layers of check valves. The third design is based on two TiNi/SU-8 composite structures, with TiNi as an actuation element, and SU-8/Si as a spring-back structure. The three types of micropump structures were fabricated based on the conventional MEMS processes.
The in-plane motion of microelectrothermal actuator ("heatuator") has been analyzed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni metal is about ~60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they provide a relatively large deflection and large force, for a low operating temperature and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process conditions have been optimized to obtain stress-free films suitable for microelectromechanical systems applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilizing the heatuator have also been fabricated and tested.
TiNi films were deposited on silicon by co-sputtering TiNi target and a separate Ti target at a temperature of 450°C. Results from differential scanning calorimeter, in-situ X-ray diffraction and curvature measurement revealed clearly martensitic transformation upon heating and cooling. Two types of TiNi/Si optical micromirror structures with a Si mirror cap (20 micron thick) and TiNi/Si actuation beams were designed and fabricated. For the first design, three elbow shaped Si beams with TiNi electrodes were used as the arms to actuate the mirror. In the second design, a V-shaped cantilever based on TiNi/Si bimorph beams was used as the actuation mechanism for micromirror. TiNi electrodes were patterned and wet-etched in a solutions of HF:HNO3:H2O (1:1:20) with an etch rate of 0.6 μm/min. The TiNi/Si microbeams were flat at room temperature, and bent up with applying voltage in TiNi electrodes (due to phase transformation and shape memory effect), thus causing the changes in angles of micromirror.
Wireless capsule endoscopy (WCE) is a new technology to evaluate the patient with obscure gastrointestinal bleeding. However, there is still some deficiency existing in the current WCE, for example, lack of ability to biopsy and precisely locate the pathology. This study aimed to prepare and characterize TiNiCu shape memory alloy thin films for developing microgripper for biopsy (tissue sampling and tagging) applications. Ti50Ni41Cu9 thin films were prepared by co-sputtering of TiNi and Cu targets, and their transformation temperatures were slightly above that of human body. Results from differential scanning calorimetry, in-situ X-ray diffraction, curvature and electrical resistance measurement revealed clearly martensitic transformation of the deposited TiNiCu films upon heating and cooling. The biocompatibility of the TiNiCu films in the simulated gastric and intestinal solutions was also studied. Results showed the release of Ni and Cu ions is much less than the toxic level and the film did not lose shape memory effect even after 10-day immersion in the simulated solutions. TiNiCu/Si micro-cantilevers with and without electrodes were fabricated using the conventional micromachining methods and apparent shape memory effect upon heating and cooling was demonstrated.
The in-plane motion of microelectrothermal actuator ("heatuator") has been analysed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni-metal is about ~60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they
provide a relatively large deflection and large force, for a low operating temperature, and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process
conditions have been optimised to obtain stress-free films suitable for MEMS applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilising the heatuator have also been fabricated and tested.