Innovative actuation principles

There is a huge need for more permforming actuators for microrobotics and microsystems. Indeed the need of always smaller and smarter microsystems and microrobots induce strong needs for actuators able to induce larger displacements, more DoF, increase the bandwidth, improve the resolution and having smaller size. Here we focussed on piezoelectric materials due to their high interest. Nevertheless, the key limitation of piezomatrials for studied applications relies in the low displacements. To tackel this key lock, we investigate two complementary ways : studying novel piezoelectric materials such as PMN-PT and novel microfabrication processes such as multilayers with thick films.

 

Study of PMN-PT [011] and [001]

This works reports the development of a duo-bimorph cantilevered actuator made of PMN-PT material and intended for large-stroke micro-scale manipulation. The principle of operation is piezoelectric, but with a series of material-induced particularities: PMN-PT is reputed for its very high piezoelectric and electromechanical coupling characteristics, but exhibits a lower coercive field which prevents driving in a fully bipolar manner. Instead of the uniaxial [001] plate, by using the anisotropic [011] cut, a positive transverse d31 piezoelectric coefficient may be exploited. This allows the extension of the structure with the applied voltage, which is particularly beneficial for micro-gripping. After an introductory part in piezo-materials and duo-bimorph structures, a comprehensive static three-dimensional displacement modeling is provided by means of constitutive matrix equations. The actuator micro-manufacturing is presented, followed by the experimental characterization. Compared to the classical PZT structures, the actuation is increased by a factor of two, up to 600 μm in the transversal plane and up to 20 μm longitudinally. Some perspectives related to 3 DoF (Degrees of Freedom) micro-manipulation tasks are finally approached.

 

 

PMN-PT [001] piezoelectric microactuator are integrated in smart Micro-Opto-Electrical-Mechanicals Systems (MOEMS). Unlike most piezoelectric materials, PMN-PT [001] can generate large-stroke out-of-plane displacement. This is due to its very high longitudinal piezoelectric coefficient of up to 4500pm/V. After an introduction on MOEMS actuation and a short description of the Reconfigurable Free Space Micro-Optical Bench (RFS-MoB) in which the studied actuator may be included is presented, a bulk microactuator is proposed. FEM simulations then follow highlighting some tradeoffs: increased displacement with the reduction in size while decreasing the optical aberration. It was observed that for actuators with surfaces over 500x500μm2 and 200μm in thickness, displacement larger than 325nm is achievable. The actuator profile impacts directly on the free surface shape and the size of the usable area of the microactuator varies in size with the applied voltage.

 

 

 

Study of PZT thick film based multi-layers

Two main fabrication processes are currently used for the fabrication of piezoelectric actuators, providing very different behaviors: (i) the use of a bulk lead zirconate titanate (PZT) layer and (ii) the use of thin film growth. In this paper, we propose a trade-off between these two extreme processes and technologies in order to explore the performance of new actuators. This resulted in the design and fabrication of thick film PZT unimorph cantilevers. They allowed a high level of performance, both in the static displacement) and dynamic (first resonance frequency) regimes, in addition to being small in size. Such cantilever sizes are obtained through the wafer scale bonding and thinning of a PZT plate onto a silicon on insulator wafer. The piezoelectric cantilevers have a 26 μm thick PZT layer with a 5 μm thick silicon layer, over a length of 4 mm and a width of 150 μm. Experimental characterization has shown that the static displacements obtained are in excess of 4.8 μm/V and the resonance frequencies are up to 1103 Hz, which are useful for large displacements and low voltage actuators.

 

Samples of publications

Vincent Chalvet, Didace Habineza, Micky Rakotondrabe and Cédric Clévy, 'Hysteresis characterization of novel thick-film PZT microactuators', Elsevier Physica B: Condensed Matter (Physica B), accepted 2015.

Alex Bienaimé, Vincent Chalvet, Cédric Clévy, Ludovic Manuel-Gauthier, Thomas Baron and Micky Rakotondrabe, 'Static / dynamic trade-off performance of PZT thickfilm micro-actuators', IOP - Journal of Micromechanics and Microengineering(JMM), 25 075017 doi:10.1088/0960-1317/25/7/075017.

D. A. Ciubotariu, C. Clévy, I. A. Ivan  and P. Lutz, Shape Behavior analysis of a PMN-PT [001] actuated MOEMS micro-mirror, IEEE/ASME - AIM International Conference on Intelligent Mechatronics, Busan, Korea, 2015.

D. A. Ciubotariu, C. Clévy, I. A. Ivan  and P. Lutz, Actuated MOEMS Micro-Mirror based on PMN-PT Piezoelectric Material, ISOT International Symposium on Optomechatronic Technologies, 2014.

D. A.Ciubotariu, I. A. Ivan, C. Clévy and P. Lutz, Size-dependent Analysis and Experiments of Bulk PMN-PT [001] Piezoelectric Actuator for MOEMS Micro-Mirrors, IEEE/ASME AIM International Conference on Advanced Intelligent Mechatronics, Besançon, France, 2014.

 

People involved

Joël Agnus (SPECIMEN team),  Cédric Clévy, Adrian Cuibotariu, Philippe Lutz, Micky Rakotondrabe

 

Contact

Cédric Clévy, cclevy 'at' femto-st 'dot' fr