Design, characterization and fabrication of the MEMS micro-grippers
Samples for MEMS microstructures and for the materials were characterized by microphysiscal characterization techniques: nanoindentation, AFM, and by SEM, electrical and thermal measurements. For the preliminary experimental technological processes we used silicon substrate and different sacrificial layers (SiO2, Omnicoat) and structural materials (biocompatible polymers as SU8, metals: Cr/Au, Au, polysilicon), and specific micromachining techniques. We realized the masks design and the manufacturing. The design were realized using CLEWIN software and the physical masks were manufactured. Preliminary experimental technological processes were performed.

• Characterization and testing of the materials and the fabrication process for MEMS micro-gripper manufacturing for microrobotic applications

Different conditions were used for the preparation of the SU-8 polymer samples in order to investigate the material properties. We investigated polymeric SU-8 samples prepared on a silicon substrate and hard-baked on a hot plate at different temperatures: 125°C, 165°C, 185°C, 195°C, 205°C and 215°C.
The nanoanalysis of mechanical and tribological properties of polymeric layers at different temperatures using Atomic Force Microscope (AFM) and nanoindentation were realized by the UTC-N and IMT Bucharest partners. A thermal stage was used by the UTC-N to control the temperature of investigated samples in the range of 20°C to 100°C using a Peltier system.
The mechanical properties like hardness and modulus of elasticity and the measurements of their behavior at different temperatures were analyzed.

Figure 1 AFM 3D image of the SU8 layer hard-baked at 195°C.


Figure 2 Modulus of elasticity vs applied temperature

Figure 3 Hardness vs applied temperature


• Design and simulation of MEMS micro-grippers

We realized the design and simulations of MEMS micro-grippers based on cascaded chevron V-shaped electro-thermal actuators. The FEM simulations were realized using Coventorware 2014 software tool. Coupled analyses electro-thermo-mechanical were performed in order to analyze the structure behavior.
The micro-grippers were designed using the principle of electrically driven thermal actuation in the normally open operating mode. The micro heaters are embedded in two polymer layers for electrically isolation and to improve thermal efficiency and to reduce out-of-plane displacements.

Figure 4 Schematic design of the SU-8 micro-gripper normally open;

                            a)                                                                         b)
Figure 5
FEM coupled electro-thermo-mechanical simulations results: a) Temperature distribution for 22 mA; b) The in-plane deflections at 22 mA (Coventorware 2014 simulation)


Fabrication of the micro-grippers

The micro-grippers were fabricated using biocompatible materials, such as SU-8 polymer used as structural layer and based on a wet release using the Omnicoat stripper.

Figure 6 Optical microscope picture of the fabricated electro-thermal SU-8 and Cr/Au/Cr micro-gripper in IMT Bucharest.


• Dissemination of the results

Scientific papers and conference presentations, patent request:

- M. Al Zandi, R-C. Voicu, R. Muller, C.Wang, Testing and Characterisation of Electrothermal Microgrippers with Embedded Microheaters,  Proc. of Symposium on Design, Test, Integration & Packaging of MEMS/MOEMS-DTIP2016, Budapest, pp. 256-260, 2016

- R-C. Voicu, Design, numerical simulation and experimental investigation of an SU-8 microgripper based on the cascaded V-shaped electrothermal actuators, Journal of Physics: Conference Series (JPCS) vol. 757 no. 1, 2016, 012015

- R-C. Voicu, M. Pustan, R. Gavrila, C. Barleanu, R. Muller, Nanomechanical characterization and thermal investigations of SU-8 biocompatible polymer used for MEMS microgrippers fabrication, Book of abstracts 11th International Conference on Surfaces, Coatings and Nanostructured Materials (NANOSMAT2016)

- R-C. Voicu, C. Tibeica, R. Müller, A. Dinescu, M. Pustan, C. Birleanu, Design, Simulation and Testing of Polymeric Microgrippers with V-shaped Electrothermal Actuators and Encapsulated Heaters, Proc. of IEEE International Semiconductor Conference CAS 2016, 10-12 October Sinaia, 2016, pp. 89-92

- D. Ulieru, X. Vila, A. Topor, “The innovative micromanufacturing solutions of high sensitivity actuators mechanical structure for micro-manipulation”, Innovation Village Section, 24/27 Oct.2016, Book of Abstracts, ALPEXPO, Grenoble, Franta

- M. Al-Zandi, C. Wang, R. Voicu, R. Muller, Measurement and Characterisation of Displacement and Temperature of Polymer Based Electrothermal Microgrippers, Microsystem Technologies, Accepted: 17 January 2017,  DOI 10.1007/s00542-017-3298-8

- R-C. Voicu, C. Tibeica, R. Müller, A. Dinescu, M. Pustan, C.Birleanu, SU-8 Microgrippers based on V-shaped Electrothermal Actuators with Implanted Heaters, Romanian Journal of Information Science and Technology (ROMJIST) Vol. 19 no. 3, pp. 269-281, 2016

- M. Pustan, R. Voicu, C. Birleanu, F. Rusu, S. Craciun, Analysis of Temperature Effect on Mechanical and Tribological Properties of SU-8 Photoresist Material, Book of abstracts, 10-th International Conference on Materials Science & Engineering BRAMAT2017, 8 - 11 March 2017

- patent request OSIM nr. A/00360/20.05.2016: „Process of fabrication of electro-thermally actuated mems devices with metallic layer embedded in SU-8 polymer used as end-effectors for micromanipulation”, Inventor(s): R. C. Voicu; R. Muller;