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Materials and Fabrication Technology

Development of Micro- and Nano-fabrication Technologies: including controlled nano-fabrication, inkjet micro-fabrication, 3D fabrication by micro-electro-discharge machining, catalytic chemical vapor deposition of carbon nanotubes, Si nanowire growth, high resolution lithography and microscopy, microfluidic devices.

Faculty involved:

Research Topics include:

Carbon Nanotubes

Carbon nanotubes, nanometer-diameter tubes made of carbon atoms, have been gaining ever-increasing popularity since their discovery in 1991 due to their outstanding electronic and mechanical properties. Nanotubes can be used in a wide range of applications including electronic devices such as quantum dots and transistors, electron emitters for flat-panel displays and electron-beam systems, chemical and biological sensors, light-weight composites and nanoscale actuators to name a few.

Electron sources

Electrons can be emitted from a material into vacuum by heating the material to very high temperatures (thermionic emission), the application of a strong external field (field-electron emission), illumination by light (photo-electron emission), or a combination of these. Electron sources are in high demand in applications such as vacuum tubes, electron microscopy and lithography equipment for micro/nanofabrication, field-emission displays, synchrotrons, electron holography and interferometry, and vacuum nano-electronics.

Flexible Electronics

Inkjet Technology

Inkjet technology printing provides a very versatile and low-cost microfabrication capability that has attracted significant research and industrial interest. Inkjet technology can be used to pattern a variety of liquids including polymers, proteins, and various solvents. This technique is used for non-contact patterning onto rigid, flexible, rough, smooth, and 3-D substrates. This process is accurate, high resolution, high speed, and consumes very little material as compared to a lithographic process. As a result, inkjet fabrication can be used for rapid prototyping and is capable of producing large batches of device variants that can later be grouped and evaluated based on various performance characteristics. The inks can be fused with nanostructures such as nanowires, nanotubes, and quantum dots to modify material properties targeting new applications. Inkjet technology has already been widely applied to the fabrication of polymer transistors, organic light emitting diodes (OLEDs), artificial tissue scaffolds, polymer sensors, and many other devices. MiNa members are using this technology to fabricated polymer based devices such as transistors, and chemical sensors. As well, we are using this technology to explore novel frontiers of biology such as constructing tissue scaffolds and printing cells.

Micro electro-discharge machining

Micro electro-discharge machining (micro-EDM) utilizes high-frequency pulses of ultimately miniaturized spark discharge to thermally remove the target material using microscopic electrodes. Micro-EDM is a very powerful technique for micro-scale engineering because it can be used to micromachine any type of electrical conductors. This capability can potentially be exploited to vastly expand the material base of MEMS, offering a variety of new application opportunities for MEMS. The research is pushing the limit toward high throughput and nano domain and exploring the application with a focus on biomedical devices such as sensor-integrated antenna stents.


Organic Materials

Research Projects include:

The demand for multifunctional and high-performance integrated circuits and systems has necessiated three-dimensional (3D) integration with through silicon via (TSV) technology. The thermomechanical stress originating from the mismatch in the coefficient of thermal expansion of Cu and silicon is a serious concern on mechanical reliability and electrical variability.
The thermomechanical stress originating from the mismatch in the coefficient of thermal expansion of Cu and silicon is a serious concern on mechanical reliability and electrical variability. This project investigates the stress distribution dependence on TSVs diameters and operation temperatures using micro-Raman and COMSOL simulations, and the impact on the keep-out-zone.
Development of an Artificial Mechanical Skin Model for Microneedle Insertion Profiling
We develop a new mechanism for changing the architecture of microfluidic channels during device operation. Two co-streaming fluids are separated through a temporal wall using targeted gel formation inside a microfluidic channel. We derive explanations for this mechanism including scaling arguments for the wall thickness.
Plants capture photons very efficiently. Can we learn from them in making photovoltaic devices? We are investigating the use of photosynthetic protein complexes in solar cells, with the aim of creating very low cost solar cells.
3D integration of integrated circuits is one of the major approaches in research to increase packing density, communication bandwidth and to reduce wire length and energy consumption. Through silicon via is one of the key technology in achieving 3D integration. Cu is used to fill TSVs, which also introduce thermal mismatch stress in the surrounding Si. This project investigate stress dependence on TSV microstructure and annealing process.
This project is in collaboration with Texas Instruments. It is to systematically investigate P diffusion behavior in SiGe and SiGe:C.
A technology for 3D printing of biological tissue constructs that will better mimic the human physiology and expedite the drug discovery process. The first stage of this work is to develop a disposable and bio-compatible droplet-on-demand (DOD) system.
We systematically study SiGe interdiffusion: 1) we established a unified interdiffusivity model for SiGe interdiffusion under relaxed or tensile strain over the full Ge content range from experimental data and diffusion theories. 2) We will investigate the impact of compressive strain on SiGe interdiffusion in middle to high Ge range. 3) We will study how interdiffusion depends on different dopants and doping levels.
Contractile polymers are applied to the tips of neuro-vascular catheters in order to help them navigate through the complex blood vessels found in the brain.
It is well known that carbon nanotubes and arrays of metal nanowires are ultra-strong. What is less well known is that voltage can be applied to make these materials contract and expand, creating impressive muscle like actuation. We are studying this new method of actuation and its initial applications.
Our research group is developing a variety of sensing devices fabricated using inkjet printing. We are exploring physical and chemical sensing technology for applications in air quality monitoring, structural health monitoring, breath analysis, and other important applications.
A significant challenge in research on nanostructures is the lack of sufficient control over the fabrication processes. Therefore, an important aspect of our research is the study of nanostructure fabrication processes with the goal of achieving higher levels of control and reproducibility.
High-resolution imaging, in particular using electron microscopes, is an integral part of device research. For nanoscale structures, artefacts such as those arising from sample charging and contamination deposition can severely affect the imaging process.
We use techniques ranging from classical, continuum modeling, to molecular dynamics, to quantum mechanical simulations using the density functional theory and first-principles techniques such as the Hartree-Fock method. We investigate the mechanical properties, electronic structure, transport characteristics and optical properties of nanodevices.
Compared to other patterning techniques, inkjet printing provides a very versatile and low cost microfabrication capability that can be used to implement organic electronic devices including printable sensors, transistors, LEDs, and photovoltaics. Inkjet technology can be used to pattern a variety of liquids including polymers, proteins, and various solvents. Inkjet patterns can be made on a variety of substrates and in 3D.
Inkjet patterning of mammalian cells
We design microfluidic environments for targeted investigations of colloid transport. Focus of this work are particle-particle interactions, as well as particle-wall interactions. This study will lead to design recommendations for robust microfluidic devices.
We develop methods to enhance current microfabrication technologies. Focus of this work is on material functionality and user friendliness.
Advanced Fabrication
Reversible cell trapping in microfluidic channels using hydrogels
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Application of printing methods in producing organic transistors has promised low-cost electronics, but a printed transistor has a poor performance due to the thick semiconductor layer. Also, most of organic transistors operate at high voltages (> 40V). We are investigating two types of organic transistors, OMESFET and dual gate transistor, to overcome the voltage problem and enhance the performance in a thick film transistor.
A magnetically actuated MEMS scanner with a microfabricated ferromagnetic nickel platform and thermosetting polydimethylsiloxane (PDMS) microlens is demonstrated. The device is driven by an external AC magnetic field, eliminating chip circuitry and thermal deformation from joule heating. The resonant frequency of 215.2 Hz and scanning angle of 23 of the scanner have been demonstrated.
Protein adsorption at the biomaterial-tissue interface is the first and critical event that initializes a cascade of host responses, including platelet activation, blood coagulation, and complement activation.1 Many approaches have been used to prevent such non-specific biological interactions.This research is investigating an engineering surface that uses micromechanical vibration to minimize protein adsorption.
By embedding low dimensional (0D, 1D, 2D) materials such as nanowires, nanotubes and quantum dots in polymers, we want improve the conversion efficiency and extend the use of solar energy, as a viable clean energy solution. Significant improvements in photocurrent and photoabsorption of polymers doped with carbon nanotubes are promising for nanocomposite solar cells.