Transfer Method of Carbon Nanotube Film for Embedded Transparent Electrode

We describe new transfer method of carbon nanotube (CNT) film onto the poly-dimethysiloxane (PDMS) based on the poor adhesion between Si wafer and Au layer. To combine the CNT film with the polymer-MEMS field, it is required to transfer CNT film onto the polymer substrates. CNT film was fabricated by vacuum filtration method and was transferred onto the Au-deposited Si wafer. Using photolithography process, CNT film was patterned and PDMS is pouring and curing on the wafer. After peeling off the PDMS, patterned CNT film was transferred which was embedded into the PDMS. The possibility of embedded CNT film in the micro system was demonstrated in the application of electro-thermal actuator.

High Throughput Continuous Fabrication of Large Surface Area Microstructured PDMS

Rapid creation of devices with microscale features is a vital step in the commercialization of a wide variety of technologies, such as microfluidics, fuel cells and self-healing materials. The current standard for creating many of these microstructured devices utilizes the inexpensive, flexible material poly-dimethylsiloxane (PDMS) to replicate microstructured molds. This process is inexpensive and fast for small batches of devices, but lacks scalability and the ability to produce large surface-area materials. The novel fabrication process presented in this paper uses a cylindrical mold with microscale surface patterns to cure liquid PDMS prepolymer into continuous microstructured films. Results show that this process can create continuous sheets of micropatterned devices at a rate of 3.94 in2/sec (100 mm2/sec), almost an order of magnitude faster than soft lithography, while still retaining submicron patterning accuracy.

Analytical Solutions for the Static Instability of Nano-Switches Under the Effect of Casimir Force and Electrostatic Actuation

This paper deals with the problem of static instability of nano switches under the effect of Casimir force and electrostatic actuation. The nonlinear fringing field effect has been accounted for in the model. Using a Galerkin decomposition method and considering only one mode, the nonlinear boundary value problem describing the static behavior of nano-switch, is reduced to a nonlinear boundary value ordinary differential equation which is solved using the homotopy perturbation method (HPM). In order to ensure the precision of the results, the number of included terms in the perturbation expansion has been investigated. Results have been compared with numerical results and also with previously published analytical results. It was observed that HPM modifies the overestimation of N/MEMS instability limits reported in the literature and can be used as an effective and accurate design tool in the analysis of N/MEMS.

Investigation of Oxide-Removal of Various Metal Particles for Fabricating MEMS-Based Corrosion Sensor

Recently, our research group has proposed a MEMS-based solid state corrosion sensor, which is based on embedding metal particle into elastomeric polymers to form a composite-based sensing material. The chemical and dimensional properties of the metal particles and polymer matrix will provide the tailorability in sensor sensitivity, selectivity, time response, and operating life-span. However, the oxidization of metallic particles prior to embedding is adverse for electrical transduction of such sensor. This paper will be based on the investigation of chemical etching protocols used to remove the oxide coating from metal particles without adversely alter the particle itself. The etching process must also be compatible with common MEMS fabrication processes and not limited by the wide range of particle sizes used (30nm–100um). More specifically, metal particles such as Titanium, Aluminum, Nickel, and Stainless Steel are currently being used and investigated.

Thermoplastic Fusion Bonding of Polymer-Based Micro Devices Using a Pressure Cooker

A novel method of thermoplastic fusion bonding (TPFB), or thermal bonding, for polymer fluidic devices was demonstrated. A pressure cooker was used in a simple sealing and packaging process with precise control of the critical parameters. Polymer devices were enclosed in a vacuum-sealed polymer container. This produced an even pressure distribution and a precise temperature boundary condition over the whole surface of the device. Deformation indicators were integrated on the devices to provide a rapid means of checking deformation and pressure distribution with the naked eye. Temperature, pressure, and time are the fundamental parameters of TPFB. The temperature and pressure are dominated by the material and contact area of the device. The temperature and pressure can be manipulated by controlling the water vapor pressure. The boiling solution guarantees an accurate, constant temperature boundary condition. Time can be eliminated as a variable by choosing a sufficient time to achieve good bonding, since there was no apparent damage to the microstructures after one hour. This new method of TPFB was demonstrated for sealing and packaging a PMMA (polymethylmethacrylate) microfluidic device. Good results were obtained using the vacuum sealed polymer container in the pressure cooker. This method is also suitable for scaling up for mass production.

Dynamic Pull-In Instability of Initially Curved Microbeams

In this study, dynamic pull-in instability and snap-through buckling of initially curved microbeams are investigated. The microbeams are actuated by suddenly applied electrostatic force. A finite element model is developed to discretize the governing equations and Newmark time discretization is employed to solve the discretized equations. The static pull-in behavior is investigated to validate the model. The results of the finite element model are compared with finite difference solutions and their convergence is examined. In addition, the influence of different parameters on dynamic pull-in instability and snap-through buckling is explored.

High Pressure On-Chip Valves for Thermoplastic Microfluidics

A high-pressure microvalve technology based on the integration of discrete elastomeric elements into rigid thermoplastic chips is described. The low-dead-volume valves employ deformable polydimethylsiloxane (PDMS) plugs actuated using a threaded stainless steel needle, allowing exceptionally high pressure resistance to be achieved. The simple fabrication process is made possible through the use of poly(ethylene glycol) (PEG) as a removable blocking material to avoid contamination of PDMS within the flow channel while yielding a smooth contact surface with the PDMS valve surface. Burst pressure tests reveal that the valves can withstand over 24MPa without leakage.

A Compact Nanostructure Integrated Pool Boiler for Microscale Cooling Applications

An efficient cooling system consisting of a plate, on which copper nanorods (nanorods of size ∼100nm) are integrated to copper thin film (which is deposited on Silicon substrate), a heater, an Aluminum base, and a pool was developed. Heat is transferred with high efficiency to the liquid within the pool above the base through the plate by boiling heat transfer. Near the boiling temperature of the fluid, vapor bubbles started to form with the existence of wall superheat. Phase change took place near the nanostructured plate, where the bubbles emerged from. Bubble formation and bubble motion inside the pool created an effective heat transfer from the plate surface to the pool. Nucleate boiling took place on the surface of the nanostructured plate helping the heat removal from the system to the liquid above. The heat transfer from nanostructured plate was studied using the experimental setup. The temperatures were recorded from the readings of thermocouples, which were successfully integrated to the system. The surface temperature at boiling inception was 102.1°C without the nanostructured plate while the surface temperature was successfully decreased to near 100°C with the existence of the nanostructured plate. In this study, it was proved that this device could have the potential to be an extremely useful device for small and excessive heat generating devices such as MEMS or Micro-processors. This device does not require any external energy to assist heat removal which is a great advantage compared to its counterparts.

Experimental Study of Structure-Electrical Transport Correlation in Single Disordered Carbon Nanowires

We present experimental results characterizing the changes in electrical transport of single disordered carbon nanowires (diameter 150–250 nm) to the changes in microstructure within the nanowires induced by synthesis temperature. The material system studied is a nanoporous, semiconducting disordered carbon nanowire obtained from the pyrolysis of a polymeric precursor (polyfurfuryl alcohol). Unlike the other allotropes of carbon such as diamond, graphite (graphenes) and fullerenes (CNT, buckyballs), disordered carbons lack crystalline order and hence can exhibit a range of electronic properties, dependent on the degree of disorder and the local microstructure. Such disordered carbon nanowires are therefore materials whose electronic properties can be engineered to specifications if we understand the structure-property correlations. Using dark DC conductivity tests, measurements were performed from 300K to 450K. The charge transport behavior in the nanowires is found to follow an activation-energy based conduction at high temperatures. The conductivity for nanowires synthesized from 600°C to 2000°C is calculated and is linked to changes in the microstructure using data obtained from SEM, TEM and Raman spectroscopy. The electrical properties of the nanowire are shown to be linked intrinsically to the microstructure and the degree of disorder, which in turn can be controlled to a great extent just by controlling the pyrolysis temperature. This ability to tune the electrical property, specifically conductivity, and map it to the structural changes within the disordered material makes it a candidate material for use in active/passive electronic components, and as versatile transducers for sensors.

Experimental Approach for Developing and Testing Predictive Self-Assembly Models

Testing methods and apparatus for studying capillary self-assembly processes are presented. This system permits the control of key self-assembly process variables so that relationships between process rates and yields and the process variables can be tested. Part arrival energies and angles are controlled by dropping through a fluid at terminal velocity onto fixed substrate binding sites. Using this system, the assembly probability at the low energy limit is shown to match a simple area fraction relationship.