Magnetic nanocrystal modified epoxy photoresist for microfabrication of AFM probes

MAGNETIC NANOCRYSTAL MODIFIED EPOXY PHOTORESIST FOR MICROFABRICATION OF AFM PROBES

Nanocomposites based on an organic polymer and inorganic nanocrystals (NCs) represent a class of high impact functional materials able to convey the unique size and shape dependent properties of nano-objects to highly processable resists.[1] In this work, a novel magnetic nanocomposite based on a negative tone epoxy photoresist and magnetic colloidal Fe2O3 NCs has been manufactured for fabricating AFM probes. Epoxy-type photoresist grant superior lithographic performances when patterned by standard near- ultraviolet (UV) optical lithography, providing structures with high aspect-ratio and nearly vertical sidewalls. Such resists are at present employed in optical and micromechanical applications for the fabrication of optical waveguides, microfluidic systems and scanning probes.[2] However, these materials lack of any inherent functionality, e.g. electrical conductivity, luminescence, magnetism, piezoresistivity and dielectricity. Hence, the incorporation of NCs can confer them new properties maintaining the patterning resolutions required for the manufacturing of highly miniaturized devices. These added properties can be interesting for the fabrication of novel micro/nanoelectromechanical systems (MEMS/NEMS). The current challenge consists on incorporating NCs in the photoresist host matrix to add functionality preserving at the same time the polymer photostructurability. The NC addition has relied on the efficient dispersion of pre-synthesized functional nanosized fillers into the pre-made epoxy photoresist, by using a common solvent as recently reported by the authors in the incorporation of highly luminescent CdSe@ZnS NCs in the same epoxy photoresist.[3] Here, the magnetic properties, UV-photostructurability and mechanical characteristics of the nanocomposite have been investigated. The results show that, after the incorporation, the Fe2O3 NCs preserve their magnetism which is conveyed to the photoresist and retained after the UV-lithography process (Figure 1).

2010

High-aspect ratio three-dimensional photoresin-based microstructures doped with luminescent nanocrystals

Jürgen Brugger, Vahid Fakhfouri

Incorporation of nanoparticles into photostructurable polymer materials enables the engineering of novel, highly integrated micro/nanosystems (MEMS/NEMS) with enhanced intrinsic functional properties. For instance, nanoparticles with (semi)conducting, optical or magnetic properties can be incorporated into polymers in order to convey their inherent functionalities to the final material, which can then be exploited for sensor and actuator applications. The current challenge is two-fold: (a) the incorporation of the functional nanoparticles into the polymer matrix and (b) the maintaining of the structurability of photosensitive polymers by UV lithography. In this paper we present a novel approach to further advance this field by combining luminescent nanocrystals (NCs) of cadmium selenide coated by a shell of zinc sulfide (CdSe@ZnS) with epoxy-based photosensitive resins. This class of material is well-known for polymer MEMS applications due to its superb structurability by UV lithography and mechanical properties. Here, colloidal methods have been used to provide luminescent CdSe@ZnS NCs with tunable size, exhibiting size-dependent optoelectronic properties. The presence of an organic ligand shell makes the NCs soluble in organic solvents and thus enables their processing and incorporation into polymers. The luminescent NCs (4.7 nm) were successfully incorporated in the epoxy-based resin by exploiting their solubility in a suitable common solvent. The NC-doped resin has been spin-coated on a silicon wafer, baked, exposed to UV light through a mask and developed. The same processing was applied to un-doped resin used as reference material. The obtained structures were inspected by means of optical, scanning electron, fluorescent and atomic force microscopy, as well as surface profilemetry. The results confirm the overall UV-structuring capability of the modified polymer. The emission properties of the NCs were demonstrated to be retained upon incorporation in the resin and spin coating. The luminescent properties of the NCs were retained after patterning by UV photolithography, although some aggregation of NCs was observed. The presence of organic ligand shell at the colloidal NC surface shows to be relevant for the subsequent processing of the doped photo-resin. The presented route looks promising for the microfabrication of polymer MEMS with inherent functionalities. Further optimization needs to be implemented also in view of a possible extension to incorporation of different types of colloidal NCs.

2006

Improved and new properties of resist materials by doping with nanoparticles and nanocrystals

Jürgen Brugger, Vahid Fakhfouri

Increasing interest in specific applications in the field of micro- and nano-electromechanical systems (MEMS and NEMS) has raised the request for new functional polymeric materials. Epoxy based photoresists are being broadly used for the fabrication of micromechanical devices and for the definition of patterns with high aspect ratio in the micrometer scale. SU-8, the well known thick photo resist with superior lithographic properties over a wide range of thicknesses, have made a tremendous impact on the development in this field by simple fabrication of permanent plastics elements with vertical sidewalls and a high aspect ratio. For new low cost applications organic materials are required which can be patterned and exhibit properties comparable to inorganic materials, such as high hardness, magnetism, conductivity or luminescence. For the manufacture of polymer waveguide systems materials with comparable lithographic processing but with sufficient difference in the refractive index are required. Hybrid materials consisting of inorganic nanoparticles in polymer matrices represent a novel class of materials for nano patterning with unique properties, which arise from the synergism between the properties of both components. The resulting novel materials can be processed and patterned using established techniques whereas the incorporated nanoparticles and nanocrystals convey their inherent functionalities and properties to the final material or composites. The suitability of silica epoxy photosensitive material as cladding material for waveguiding application and luminescent nanocrystal doped epoxy resist as model composite for the investigations of different core/ shell surface modifying methods and for light sensing and emitting application will be demonstrated.

2007

High-aspect ratio three-dimensional photoresin-based microstructures doped with luminescent nanocrystals

Jürgen Brugger, Vahid Fakhfouri

2006

MAGNETIC NANOCRYSTAL MODIFIED EPOXY PHOTORESIST FOR MICROFABRICATION OF AFM PROBES

Jürgen Brugger, Cristina Martin Olmos

2010