F&E3/English

Department FuE3: Replication

Head of department: PD Dr. Matthias Worgull

The aim of our research activities is the replication of micro and nanostructures. Work is performed in the two topics

• Nano- and Microreplication

and

• Microthermoforming

The activities in research and development are focused on the following replication processes:

• Micro Hot Embossing
• Nanoimprint
• Microthermoforming
• Ultrasonic Embossing

We are partly integrated in European research projects like COTECH (Converging Technologies) with the aim to develop efficient replication techniques.

Our technology is also available for external user within the frame of the KNMF (Karlsruher Nano Micro Facility) and EUMINAfab.

Current Team

• PD Dr. Matthias Worgull (Head of department)
• Heinz Dinglreiter (Groupleader Microthermoforming)
• Marc Schneider (Installation- and Processmanager)
• Alexander Kolew (Post-Doc)
• Norbert Schneider (PhD-Student)
• Michael Hartmann
• Julia Bur (Diploma student)
• Raschid Ezzat (Diploma student)
• Christoph Herrmann (HiWi)
• Ludmilla Popp (HiWi)
• Gerlinde Utsch (HiWi)

Nano- and Microreplication

We apply hot embossing and nanoimprint for the replication of micro and nanostructures. 5 hot embossing machines are available allowing the replication of structures on an area of max. 8 inch. The process of hot embossing is characterized by a high flexibility and a large diversity of process variations, like double sided positioned embossing or replication of through holes. The equipment of the hot embossing machines allows the fast replication of prototypes in different polymers up to replication of small series.

The diversity of suitable mold inserts corresponds to the lithographic structuring methods available at IMT, which are Deep X-Ray Lithography (LIGA), UV Lithography and Electron Beam Lithography. As an alternative to the lithographic processes mold inserts can also be fabricated by micromechanical machining like milling or also by laser machining. Already existing structures, like structures fabricated by etching processes can be copied into nickel mold inserts by electroplating.

An advantage of hot embossing is the fast change of the molding material by the use of different polymer films during each embossing cycle. The diversity of the used polymers comprises the group of thermoplastic polymers:

• Amorphous polymers like PS, PMMA, COC, PC, PSU
• Semicrystalline polymers like PP, POM, PET, LCP, PEEK
• Low-melting glass
• Metallic glass, amorphous metalls
• Feedstock for ceramic or metallic parts
• Metallic foils and duromers
• Renewable biodegradable polymers: liquid wood, polylactide

Microthermoforming

Microthermoforming is a process developed at IMT for the low cost fabrication of flexible, thin-walled hollow structures of polymer films.

With an hot embossing tool an approximately 10 – 50 µm thin polymer film will be heated up to the thermoelastic state and will be formed under gas pressure into evacuated micro cavities of a mold insert.

Actual research topics are

• Development of the technology from laboratory use up to the technology for microthermoforming machines for serial fabrication (in cooperation with Wickert Press / Landau)

• Development and engineering of tools for thermoforming

• Process development for the fabrication of CellChips® by microthermoforming for tissue engineering. (In collaboration with TU Ilmenau and IBG / KIT)

• Thermoforming of prestructured polymer films for the fabrication of 3 dimensional microstructures with a sub-micron or nanostructure on their surface. In a first step a polymer film is structured by hot embossing. In a second step this structured polymer film is formed in a 3 dimensional shape by microthermoforming without any destruction of the structures. By this process chain for example fluidic channels can be additionally structured with nanostructured hydrophilic or hydrophobic surfaces, at the bottom and even at the sidewalls.

• Development of micro blow molding for the fabrication of 3 dimensional hollow structures. By this process the replication of hollow structures like micropipes with nanostructured surfaces inside will be developed.

Ultrasonic structuring

The ultrasonic technology is characterized by excellent properties like short process times, low energy consumption, or repeatability of the welding or punching results. Further also polymers can be processed in an efficient and gentle way.

A new field of application of ultrasonic structuring is the field of Tissue Engineering. This new research area refers to an interdisciplinary approach of the science in biology, materials research and engineering. The so called CellChip® was developed at the Forschungszentrum Karlsruhe and is characterized by a kind of scaffold structures for the three dimensional cultivation of cells. The fundamental idea of the planar arrangement of identical micro container with porous bottoms is the consistent supply of the cells inside the containers with culture medium.

Within the frame of the research activities for the fabrication of CellChips the structuring with ultrasonic vibration so called ultrasonic embossing could be determined as a suitable structuring method. With this method microstructures can be replicated in polymer in a time period of a few seconds. Similar to the hot embossing process a thin is heated up and the metal mold insert will be replicated by an embossing step. The energy needed for the melting of the polymer film will be applied by ultrasonic vibration of the sonotrode. Typical amplitudes of the oscillation are in a range of several 10 µm and a frequency of 20 up to 70 kHz. These oscillations acts on the polymer foil by the sonotrode pressing the polymer foil against the structured mold insert. Because of the cyclic deformation the polymer foil will be heated up locally and will be pressed against the structured mold insert. After a short cooling time in the range of a few seconds the microstructures can be demolded.

For the structuring by ultrasonic oscillation commercial available machines are suitable. The mold inserts can be fabricated by electroplating of Nickel or by mechanical machining e.g. in high quality steel. Suitable molding materials are thermoplastic polymer materials with high form stability.

The advantage of this process is the local structuring of already existing components like Microtiterplates without modification of the shape of the component. Ultrasonic embossing is therefore an excellent extension of the established replication processes injection molding, hot embossing, and thermoforming. Short cycle times, simple molding tools, commercial available machines and an easy handling are characteristics of this replication technology.

Role to Role structuring

Further development in nano- and microstructuring with respect to large area and high throughput is represented by role to role structuring, the newest research area of the department.