Considerations on using SU-8 as a construction material for high aspect ratio structures

This paper discusses two material aspects of SU-8 that have up till now been insufficiently documented. We present initial results on the outgassing behavior and a study on the dielectric properties of SU-8 at high bias voltage. The dielectric strength is determined to be at least 2 MV/cm. These elements are investigated in the light of plans to manufacture an SU-8 based Micro-Channel Plate (MCP). Although the outgassing properties and dielectric strength are favorable the patterning capabilities are expected to limit the use of such an MCP

Development of a conductive photoresist with a mixture of SU-8 and HCL doped polyaniline

A novel electrically conductive photoresist has been formulated to fabricate microcomponents. The developed conductive photoresist is based upon SU-8 photopolymer, an insulating negative-tone epoxy, in which protonically doped polyaniline (PANI) nanoparticles have been dispersed to enhance the electrical properties. The characteristics of this new conductive photoresist have been studied via electrical measurements. The process for preparing the conductive films from the combination of EB (Emeraldine base) PANI, SU-8 and NMP (N-methyl-2-pyrrolidinone) will be presented. Different weight percentages (wt%) of SU-8 in the above combination have been prepared and spin coated to form thin-films which have been protonated with HCl. The conductivities of the thin- films were measured using a four point probe. The highest conductivity achieved was approximately 1.6 S/cm for the mixture of 10 wt% of SU-8 25 with EB-PANI mixed with NMP. The morphology of the thin-films was studied using a scanning electron microscopy (SEM)

Fabrication and testing of polydimethylsiloxane (PDMS) microchannel for lab-on-chip (LOC) magnetically-labelled biological cells separation

Microfluidics channel of micron-to millimeter in dimension has been widely used for fluid handling in transporting, mixing and separating biological cells in Lab-on-Chip (LoC) applications. In this research, fabrication and testing of Polydimethylsiloxane (PDMS) microfluidic channel for Lab-on-chip magnetically-labelled biological cells separation is presented. The microchannel is designed with one inlet and outlet. A reservoir or chamber is proposed as an extra component of the microchannel design for ease of trapping the intended biological cells in LoC magnetic separator system. The PDMS microchannel of circular-shaped chamber geometry has been successfully fabricated using replica molding technique from SU-8 negative photoresist mold. An agglomerate-free microbeads flowing has been observed using the fabricated PDMS microchannel. Trapping of microbeads in the trapping chamber with 2.0 A current supply in the continuous microfluidics flow > 100 µL/min has also been demonstrated. In conclusion, a separation of biological cells labelled with magnetic microbeads is expected to be realized using the fabricated PDMS microchannel

Single-mode waveguides with SU-8 polymer core and cladding for MOEMS applications

Fabrication and optical characterization of single-mode polymeric embedded waveguides are performed. A specific material combination (SU-8 2005 as core and the modified SU-8 mr-L 6050XP as cladding) is chosen in order to obtain a small refractive index difference for single-mode propagation combined with the conventional fabrication method UV lithography to facilitate the integration of different types of optical detection methods on lab-on-a-chip systems. We analyze the behavior of the refractive index and carefully observe how the value of the refractive index can be tailored during processing. We show that we can fabricate waveguides with an index difference in the order of 10-3 , where both the core material and the cladding material are based on SU-8. The refractive index measurements are performed on thin polymeric films, while further optical characterizations are performed on waveguides with a height of 4.5 mum. We study the mode profiles of these waveguides and confirm that only the fundamental mode is excited. We also study the absorption spectra of the material in the wavelength range 800-1600 nm combined with cut-back measurements. We find that the waveguides have a propagation loss of 0.2-3 dB/cm in this wavelength range

Process development of the device using in-house plate-to-plate tool with nanoimprint lithography technique for biochip application

Biochip is a promising device with capabilities of performing sorting, trapping and screening a large number of biological samples in a short time. Fabrication of biochip pattern process leads to an opening study towards the development of a working biochip. The traditional photolithography process have a limitation in achieving high throughput for biochip pattern fabrication. In this research, the fabrication process of biochip pattern was developed and the imprint parameter for biochip pattern using an in-house assembled plate-to-plate tool was investigated. The biochip patterns are prepared from existing projection lithography to create the mold. Using soft lithography technique, the biochip pattern was replicated invertly in the PDMS mold. The PDMS mold and in-house plate-to-plate fulfilled the requirement for UV-NIL to imprint biochip patterns on a flexible substrate. Dimension error difference (DED) is the difference between the original design dimensions to fabricated design dimensions. DED was characterized and investigated for precise pattern transfer. UV exposure of 140 W was able to produce the satisfied imprint pattern in biochip pattern mold fabrication. However, higher UV energy caused overexposure in the resist, resulting wider width and bridging. Besides that, crack regions were found when post bake exposure parameters are not properly optimized. The DED between biochip pattern mold and PDMS mold are less compared to biochip pattern mold fabrication in the photolithography process. Critical dimension in the biochip pattern was maintained in the imprint process. However, the higher imprint force will cause an overflow of the resist on the substrate, resulting unsatisfied pattern structure. The proposed parameters for imprinting biochip patterns using in-house plate-to-plate tool are 80 N range and 20 seconds of UV exposure

A novel single-use SU-8 microvalve for pressure-driven microfluidic applications

A novel microfluidic single-use valve for fluid injection and extraction in pressure-driven applications is presented in this paper. The device consists of a thin SU-8 membrane crossed by a resistor that withstands a mechanical stress induced by a pressure difference. When the resistor heats up the membrane, the SU-8 fracture strength drastically decreases causing the valve activation. This device has been designed, fabricated using inexpensive SU-8 and printed circuit board technologies and finally characterized. The hybrid thermal–mechanical microvalve operation principle has been demonstrated and experimental results have shown the device characteristics and performance. Specifically, this design was functional at pressures of 0.8 MPa and opened in less than 3.2 s with an applied power of 280 mW. The simple fabrication process and the absence of moving mechanical parts have made the valve suitable for large-scale integration in lab-on-chip microfluidic platforms

Functionalization of Surfaces Using Photolithography and Other Techniques

Coated materials are encountered on a daily basis, and are a part of almost everything manufactured today. Despite their ubiquity, investigations on their chemical functionality and structure still provide interesting research potential. This dissertation investigates two kinds of coatings, polymeric and self-assembled monolayers (SAMs). The polymeric coatings investigated are in the form of photoresists that are used to create substrates for laser ablation. Adjusting the composition of the photoresists leads to the formation of unique structures during this laser ablation. Another application of photoresists that was studied is the creation of transferable microstructures on a flexible substrate. These microstructures, in the form of arches, are created using multiphoton absorption polymerization. The creation of a patterned SAMs substrate with the potential application as a microarray was explored. Photolithography and soft lithography approaches were tested to create these amine-functionalized surfaces. In addition, silicon nitride surfaces were investigated as a suitable substrate for alkylphosphonate SAMs. A variety of surface techniques including sum frequency generation and X-ray photoelectron spectroscopy were employed to study these surfaces and ultimately the presence of a multilayer, more than one monolayer, was found

Creating Three-Dimensional Polymeric Microstructures by Multi-Beam Interference Lithography

It is attractive to produce true three-dimensional (3D) microstructures both rapidly and economically over a large area with negligible defects for a wide range of applications. Multi-beam interference lithography is one of the promising techniques that can create periodic microstructures in polymers without extensive lithography and etching steps. This review discusses the formation of interference patterns, their dependence on beam parameters, the lithographic process, and the applications to the formation of photonic crystals. Various photoresist systems, including thick films of negative-tone and positive-tone photoresists, liquid resins, organic-inorganic hybrids, and holographic polymer-dispersed liquid crystals, are also reviewed

Harnessing multi-photon absorption to produce three-dimensional magnetic structures at the nanoscale

Three-dimensional nanostructured magnetic materials have recently been the topic of intense interest since they provide access to a host of new physical phenomena. Examples include new spin textures that exhibit topological protection, magnetochiral effects and novel ultrafast magnetic phenomena such as the spin-Cherenkov effect. Two-photon lithography is a powerful methodology that is capable of realising 3D polymer nanostructures on the scale of 100 nm. Combining this with postprocessing and deposition methodologies allows 3D magnetic nanostructures of arbitrary geometry to be produced. In this article, the physics of two-photon lithography is first detailed, before reviewing the studies to date that have exploited this fabrication route. The article then moves on to consider how non-linear optical techniques and post-processing solutions can be used to realise structures with a feature size below 100 nm, before comparing two-photon lithography with other direct write methodologies and providing a discussion on future developments

Cryogenic deep reactive ion etching of silicon micro and nanostructures

This thesis focuses on cryogenic deep reactive ion etching (DRIE) and presents how it can be applied to the fabrication of silicon micro- and nanostructures that have applications in microfluidics and micromechanics. The cryogenic DRIE process relies on inductively coupled SF6/O2 plasma at temperatures below -100 °C. Low etching temperatures can cause some photoresist materials to crack, but Al2O3 has been shown to be a very well-suited masking material for cryogenic etching. The anisotropy of the etching process is enhanced by a thin passivation layer on sidewalls that prevents lateral etching. The main parameters that are used to adjust the thickness of the passivation layer are the process temperature and the O2 flow. Under adequate conditions vertical sidewalls are obtained, whereas passivation layers that are too thin result in negatively tapered sidewall slopes. Under conditions where a passivation layer is not formed, at higher temperatures and/or without oxygen flow, the etching profiles are isotropic. On the other hand, too high oxygen flow results in over passivation. Under conditions where the sidewall is slightly over passivated, its slopes are positively tapered, while more pronounced over passivation results in the formation of black silicon (or silicon nanograss, silicon nanoturf or columnar microstructures). Typically, vertical sidewall profiles are desirable. However, this thesis shall also demonstrate the usefulness of under and over passivation regimes. Here, highly anisotropic etching conditions are utilized to create trenches with vertical sidewalls, fluidic channels with regular micropillar arrays, and high aspect ratio silicon nanopillars. An isotropic etching process is utilized during the release of aluminum heaters fabricated on top of perforated free-standing Al2O3 membranes and silicon dioxide coated thermal silicon actuators. The fabrication process of three-dimensional sharp electrospray ionization (ESI) tips takes advantage of etching conditions that result in negatively tapered sidewalls. A self-feeding ESI interface for mass spectrometry (MS) is fabricated by combining a lidless micropillar filled channel with a sharp tip. Two approaches to the fabrication of silicon nanopillars are presented, both of which are suitable for wafer-scale manufacturing. One method combines silica nanoparticles with a highly anisotropic DRIE step, while the other method relies on highly over passivating conditions in a maskless DRIE process. Due to a large surface area and efficient light absorption in UV-range, silicon nanopillar structured surfaces are utilized as sample plates in laser desorption/ionization (LDI) MS. The wetting of nanopillar structured silicon surfaces is also studied. Fluoropolymer coated nanopillar structured surfaces have a contact angle of more than 170° and are ultrahydrophobic, whereas oxidized nanostructured surfaces are completely wetting. The accurate patterning of both completely wetting and ultrahydrophobic areas side by side allows complex droplet shapes and droplet splitters to be tailored