Search

We present a versatile and scalable method for the preparation of microfluidic channels with incorporated nano patterns. Since our approach is highly industrial driven, all used methods and materials are available in common micro-fabrication environment and are available in large quantities, respectively. In comparison to other fabrication methods capable of realizing multi-level patterns, we combine nanoimprint lithography with standard photolithography, and thereby overcome the problems of limited pattern dimensions as well as fabrication time, pathing the way for a new class of microfluidic devices.

Hybrid polymers constitute a class of optical materials combining properties of inorganic glass and organic polymers. The flexible synthesis and processing allows for specific tailoring of their properties as required for the fabrication of high-performance and reliable microoptical elements. While wafer-scale fabrication of microoptics using hybrid polymers is widely used in an industrial environment, they gain ever-increasing attention in additive manufacturing and 3D printing technologies. This chapter introduces the chemical concepts behind hybrid polymers, discusses their synthesis and processing, and gives a record on their application for the fabrication of microoptical and photonic elements using established wafer-scale as well as emerging additive manufacturing processes, in particular inkjet printing and two-photon polymerization direct laser writing.

We present a new epoxy-based negative-tone dry film photoresist (DFR) for fabricating multilayer microfluidic devices using a lamination process combined with a standard photolithography technology. As proof-of-concept, a complex 3D-hydrodynamic focusing device was produced via a six-layer lamination process of 33 µm-thick DFR layers. The bonding strength of the new DFR was tested on silicon, glass, and titanium substrates, respectively. A maximum bonding strength of 37 MPa was obtained for the dry film photoresist laminated on glass. No leakage was found, and burst tests proved excellent robustness and sealing reliability of the microchannels.

This work presents a new type of high-resolution dry-film resist laminates for the fabrication of extremely thick epoxy based polymer structures. Via a lamination process a resist thickness of up to d=360@mm can be applied by one single process step. Afterwards, the dry-film resist is patterned by standard UV-lithography. An epoxy based resist mixture which contains epoxy resins, reactive diluents, additives, and a photo acid generator is deposited onto a PET supporting film by doctor blading for fabrication of the resist film. The films can be cut defect-free into favoured sheet sizes. Currently, dry-film resists with a layer thickness of up to 400@mm can be produced reproducible. With the tested d=360@mm thick dry-film resist an aspect ratio of 15:1 (height:width) has been achieved. By lamination and UV-patterning of two layers resist a master for 700@mm thick electroplated Nickel structures was fabricated. Thereby, steep side walls with an angle deviation of @a

There are two basic types of nanoimprint lithography: hot embossing using thermoplastic or thermosetting polymers and UV-based nanoimprint lithography (UV-NIL) using UV-curable polymer systems. Since the interest in UV-NIL has been constantly increasing within the last years, the need of suitable low-viscosity resists has increased, too. The availability of such materials is one key element of the UV-NIL technology. In this contribution a novel, spin-coatable polymer system for UV-NIL is presented. Suitable polymer components were evaluated using photoDSC analysis. Their ratio was adjusted in such a way that the overall dynamic viscosity of the mixture remained low which was beneficial for the flow behaviour. Film thicknesses in the range of 150-500nm could be obtained by spin-coating. The new polymer system was characterised in UV-NIL processes and in plasma etching investigations. Imprinted micrometer as well as nanometer scale patterns with feature sizes in the range of 30nm to several microns are shown.

Plano-convex microlens arrays of organic-inorganic polymers with tailored optical properties are presented. The fine-tuning of each microlens within an array is achieved by confining inkjet printed drops of the polymeric ink onto pre-patterned substrates. The lens optical properties are thus freely specified, and high numerical apertures from 0.45 to 0.9 and focal lengths between 10 μm and 100 μm are demonstrated, confirming theoretical predictions. Combining nanoimprint lithography approaches and inkjet printing enables using the same material for the microlenses and their substrates, improving the optical performances. Microlens arrays with desired specifications are printed reaching yields up to 100% and high lens reproducibility with standard deviations of the apparent contact angle under 1° and of the numerical apertures and focal lengths under 6%. Microlens arrays involving lenses with different characteristics, e.g. multi focal length, and thus focal planes separated by only few microns are printed with the same reproducibility.

An all-polymer photonic crystal slab sensor is presented, and shown to exhibit narrow resonant reflection with a FWHM of less than 1 nm and a sensitivity of 31 nm/RIU when sensing media with refractive indices around that of water. This results in a detection limit of 4.5x10-6 RIU when measured in conjunction with a spectrometer of 12 pm/pixel resolution. The device is a two-layer structure, composed of a low refractive index polymer with a periodically modulated surface height, covered with a smooth upper-surface high refractive index inorganic-organic hybrid polymer modified with ZrO2-based nanoparticles. Furthermore, it is fabricated using inexpensive vacuum-less techniques involving only UV nanoreplication and polymer spin-casting, and is thus well suited for single-use biological and refractive index sensing applications.

The high throughput and large area nanostructuring of flexible substrates by continuous roller processes has great potential for future custom applications like wire grid polarizers, antireflection films, or super-hydrophobic surfaces. For each application different material characteristics have to be considered, e.g. refractive index, hydrophobicity, or dry etch stability. Herein, we show experimental results of nanoimprint lithography resist developments focused on inkjetable and photo-curable resists suitable for high throughput production, especially roll-to-roll NIL. The inkjet deposition of the novel materials is demonstrated by the use of different state-of-the-art inkjet printheads at room temperature. A plate-to-plate process on silicon substrates was successfully implemented on a NPS300 nano patterning stepper with previously inkjet dispensed NIL resist. Furthermore, we demonstrate a throughput of 30 m min-1 in a roller NIL process on PET. Dry etching of unstructured thin films on Si wafers was performed, and it was demonstrated that the etch stability in Si is tunable to a value of 3.5:1 by a concise selection of the resist components. The surface roughness of the etched films was measured to be < 2 nm, after etching of around 100 nm of the resist films what is an essential factor for a low line edge roughness. All resists reported herein can be deposited via inkjet dispensing at room temperature, are suitable for continuous high throughput imprinting on flexible substrates, and are applicable in step-wise NIL processes with good etch resistance in dry etch processes.

The use of working stamps for nanoimprint lithography is highly interesting for a number of reasons like an increased lifetime and often a better manufacturability of the master stamp. We present results on the use of Ormostamp as a material for working stamps in UV-NIL. Imprinting properties and anti-sticking treatments have been investigated. So far a minimum feature size of 50nm can be achieved.

Graphical abstractDisplay Omitted R2R-NIL is presented with high throughput roller speeds of 30mmin-1 and good pattern fidelity.The viscosity of the novel materials is below 20mPas, enabling inkjet dispensing at room temperature.Throughput variation from 1mmin-1 to 20mmin-1 decreased double bond conversion less than 5%. We report two newly developed photo-curable resists specifically engineered for inkjet dispensing facilitating nanoimprint lithography (NIL) in a high-throughput environment. The viscosity of the novel NIL resists was adjusted especially to enable inkjet dispensing at room temperature. The novel resists can be applied either in NIL batch processes or in high throughput processes like roll-to-roll NIL (R2R-NIL). Batch-wise imprints were performed on various substrates as Si or plastics demonstrating the distinctive application versatility of the novel materials. The very fast curing speed of these materials is discussed in detail with the aid of FT-IR and photo-DSC measurements. The experiments demonstrate a high degree of double bond conversion of about 80% after curing and a fast curing in a few seconds even at a low radiation intensity of 0.2mWcm-2. The novel materials show excellent adhesion on different substrates and high optical transparency. The high throughput capability of the novel materials is demonstrated by R2R-NIL processes performed at a web speed of up to 30mmin-1.

We report on our development strategy of photo-curable resists for nanoimprint lithography (NIL) based on modularity. Starting with a basic formulation, we address two topics: the integration of fluorinated additives and the enhancement of the dry etching stability. We prove both concepts by the introduction of two different resists derived from the same basic formulation. The viscosity of the novel resist materials was optimized for inkjet dispensing at room temperature (RT). The novel resist materials can be applied either in NIL batch processes or in high-throughput roller processes. Batch-wise imprints were performed on various substrates such as Si or plastics, demonstrating the distinctive application versatility of the novel materials. Dry etching of spincoated thin films on Si wafers was performed, demonstrating an etch stability versus Si of 3.5:1 by using the resist formulation with improved etching stability. Roll-to-roll NIL at high throughput on large areas was performed with web speeds of up to 30 mmin−1 with different stamp materials. We conclude that all resists reported herein can be deposited via inkjet dispensing at RT, are suitable for continuous high-throughput imprinting on flexible substrates, and are applicable in step-wise NIL processes with good etch resistance in dry etch processes.

Graphical abstractDisplay Omitted Highlights? We present a new thermal NIL resist for high-aspect-ratio patterns via a bilayer approach. ? The resist properties are tailored by free radical polymerization of specific comonomers. ? The resist shows excellent flowability and demoulding characteristics. ? A high oxygen RIE resistance demonstrates the suitability of the resist as a masking layer. We report a newly developed thermal nanoimprint (T-NIL) resist specifically engineered for the implementation in a bilayer system rendering the fabrication of high-aspect-ratio patterns. The synthesis of the T-NIL resist was accomplished by applying a free radical copolymerization of adequate comonomers. Due to the modular architecture of the terpolymer, the rather different material properties are directly adjusted by varying the amount of the comonomers and also by tuning the polymerization conditions like temperature and the amount of initiator. Following this synthetic strategy, the Si content for a sufficient oxygen plasma resistance as well as an excellent flowability behavior for a significant reduction of the overall processing cycle time could be easily achieved. Moreover, the already good mould release properties of the pure T-NIL resist can be further improved by the addition of a small amount of a fluorinated additive leading to a very low defect rate of the imprinted structures.

One of the key elements for the successful integration of nanoimprint lithography into industrial production processes is the availability of high-performance resist materials. In this contribution we present a novel low-viscosity and fast curing UV-NIL polymer, which is applied by spin-coating and designed for wafer-scale imprinting. Systematic investigations of photocurable components and photoinitiators led to the formulation of the polymer system mr-UVCur06. Film thicknesses in the range of 50 - 500 nm with excellent quality and uniformity could be obtained by spin-coating. Its suitability for UV-NIL processes was evaluated by means of imprinting tests and plasma etching investigations. This included investigations on imprinting with hard moulds, UV curing doses, resolution, etch rates using various plasma gases and pattern transfer. The beneficial flow behaviour of mr-UVCur06 led to short UV-NIL cycle times. Patterns of several orders of magnitude with feature sizes in the range of 30 nm to several tens of micrometers could be imprinted simultaneously. An example of a pattern transfer into Si was shown, where mr-UVCur06 was used as an polymer etch mask.

We report on the fabrication by nanoimprint lithography (NIL) and performance of metal stripe waveguides embedded in a polymer, capable of supporting long-range surface plasmon polariton (LRSPP) propagation.

We present a new organic photosensitive material for volume holographic recording. Advanced material composition and sample preparation eliminates the need for a protective layer and allows layer fabrication with variable thickness and a free surface. Optimized chemical formulation results in a high energetic sensitivity, high angular selectivity and high inducible refractive index contrast. We investigate the photoresponse and nonsinusoidal refractive index profiles. We demonstrate highly resolved optical structuring with up to 8000 lines per mm. Imaging of the holographic phase gratings is accomplished by optical microscopy.

Microlens arrays fabricated by a direct ink-jet printing of UV-curable hybrid polymer are reported. A periodic pattern of polymer drops was ink-jet printed on the surface-treated glass substrate and cured in the UV-light. Using this simple technique, we demonstrated periodic arrays of almost semi-spherical microlenses of 50 μm diameter size and a focal distance of 48μm. The optical characteristics of solitary μ-lenses and arrays comprising up to 64x64 microlenses are measured both in the near- and far-field zones. Large numerical aperture and short focal distance make the ink-jet printing of microlenses very attractive for applications in optical interconnects, large 2D VCSEL arrays and pixelated imagine sensors utilizing CCD or SPAD arrays, offering thus an efficient, simple and a cheap alternative to the conventionally used photolithography technique.