Joint Laboratory on Electromechanical Transducers and Micro-converters for Medical applicationS – Lab-TMEMS

The importance of implantable or miniaturised medical devices in terms of public health is now recognised by many national and international authorities. It is a rapidly developing field with an increase of annual turnover that has been close to 10% for several years. Such devices play an important role in many medical applications and for well being such as assisting elderly or handicapped persons and helping them to remain at home, contributing to reliable diagnostics, to localised or targeted therapies or for guidance during surgery, etc… The devices addressed by this joint laboratory are miniature electromechanical converters that can transform mechanical energy into electrical energy or vice-versa. A joint platform will be setup, including modelling/design tools as well as characterisation and technological systems, in order to develop new devices. The two first developments will be:
• Implantable mechanical energy harvesters ((typ. 10×5×0,1 mm3) that use the heart’s movements to produce enough energy (mean power of 10 µWatt )so that systems can become autonomous;
• Small size ultrasonic emitting transducers to produce high intensity waves, i.e. HIFU (High Intensity Focused Ultrasound) that can locally destroy (burn) malignant tissues, more precisely brain tumours.

There are two main electromechanical conversion technologies that are compatible with the constraints imposed by miniaturisation: piezoelectric structures and devices based on electrostatic forces, i.e.cMUTs(capacitive Micromachined Ultrasonic Transducers). For energy harvesting, piezoelectricity is the best adapted because no external electrical source is required. For high intensity ultrasound generation, cMUTs have a high potential.

The Lab-TMEMS joint laboratory proposal comes after collaborations between GREMAN’s academic teams and VERMON’s R&D engineers through several projects. It aims at creating a joint platform that will reinforce collaborations in the long-term thanks to the combination of the two organisations’ expertise. This will allow to initiate work in novel fields and to extend electromechanical conversion technologies to new medical applications. During the next three years, the consortium’s objectives are to design, manufacture and validate two industrial demonstrators, one for each of the applications described above. The scientific and technological issues addressed by the joint laboratory will cover the complete value chain of the devices, i.e. modelling and design tools, material processing, MEMS technologies and finally integration.
For the HIFU cMUTs, the specificities will be:
• A novel modelling tool for high power operation,
• Choice of materials and their processing technologies adapted to high solicitations and with reduced dielectric ageing,
• 3D integration of cMUT chip with bio-compatible and low loss materials,
• Optimised electrical excitation to limit non-linear effects,

For energy harvesting devices, the specificities will be:
• Design of microgenerators that can harvest vibration energy at very low frequencies (around 10Hz) as compared to harvesters for industrial applications,
• Choice of high efficiency piezoelectric materials with and without lead,
• Depositand patterning of piezoelectric and passive layers, typically in the few tens of micrometers thickness range for which classical machining of bulk materials is not possible, which means that specific thick film technologies will be required.