Abstract: Advances in microfabrication are enabling a large variety of miniaturized implantable systems for health monitoring and deficiency treatments. Today, the new generation of pacemaker called leadless pacemaker is directly implanted on the endocardium within a heart cavity without any lead (e.g. Micra by Medtronics).
However, electrical energy lifespan of the implants (<12 years) and large size of batteries are still a problem. Funded by the European project MANpower (FP7-NMP), the objective of my PhD work was to develop a solution based on mechanical energy harvesting from the heart motion to sustainably power this new generation of pacemaker.
This application imposes several critical requirements in term of size (<1cm³), power output in range (1-10 µW), reliability, durability (>20 years) and compatibility with MRI. This talk will present a 3D energy harvesting microsystem consisting in a spring-mass-type mechanical resonator associated with an electrostatic transducer. Its originality comes from a three-dimensional architecture, whose shape fits pretty well with the cylindrical shape of the pacemaker capsule. The use of the third dimension combined with an original design enables to get a pseudo multiplication frequency effect.
To fabricate this complex three-dimensional microsystem, we developed an additive manufacturing process based on the repetition of three main steps: the micromolding of a structural material (nickel), the electrodeposition of a sacrificial material (copper) and a mechanical planarization of the layer. Identification of imperfections related to the fabrication process and the materials used allowed us to improve the design of the transducer. Moreover, many manufacturing obstacles were overcome through the implementation of dedicated instrumentation. This new process has enabled to fabricate a first three-dimensional prototype of the electrostatic MEMS made of 10 layers of nickel for a total thickness of 200 µm with a minimum in-plane pattern size of 10 µm.