Quartz-based Nanomaterials On Silicon for a Sensorized world – Q-NOSS

Piezoelectric materials are the key elements of motion sensors (accelerometers and gyroscopes) and resonators present in any wireless network sensor (WNS) node. For the Internet of Things (IoT), remote sensing and the transfer of information, to become a global reality, billions of sensors and WNS nodes have to be installed everywhere. Therefore, the increased production of piezoelectric materials in a sustainable way is to-date a milestone. To this aim, the main objective of Q-NOSS is to develop a new piezoelectric material that will change the industrial landscape by removing the current hobbles (toxicity, abundance and integration cost). This new material will be synthetized by engineering a-quartz, a classical non-polar piezoelectric, using a novel synthesis of the quartz as epitaxial thin films in order to optimize their piezo response.
Quartz is only available as bulk single crystals that are expensive to grow, firstly, and then need to be thinned and polished down to the very low thickness needed for high frequency transducers. This is a difficult process that results in minimum thicknesses of about 10 µm, which in turn limits the working frequencies of the transducers. For industrial processing using MEMs technology (with the aim to reach prices of 1€/device), thin film deposition on Si is a must. Thus, the ambition of Q-NOSS is the integration of high quality epitaxial quartz-based piezoelectrics on Si platforms using industrially scalable methods. This is a major challenge that demands bridging the gap between soft-chemistry and microfabrication techniques. The specific objectives of this project are:

Objective 1. Growth of oriented quartz thin layers with high-performance piezoelectric response.
We will implement a unified, monolithic process that will allow integrating high quality single crystal piezoelectric quartz thin films on silicon technology. We will combine bottom up CSD approach with prominent techniques in microelectronics such as MBE, in order to gain understanding and control of the nucleation and growth mechanisms of quartz films.

Objective 2. Nanostructuration of quartz piezoelectrics into 1D wires to enhance its performance.
We will create epitaxial quartz-based thin films with controllable morphologies or nanostructures, in particular vertical 1D nanowires and nanorods in order to increase the specific area and, thus, enhance the sensing properties of the future device. We will fabricate novel epitaxial quartz-based piezoelectrics nanostructures by using both soft chemistry and processing (combining bottom up and top down nanofabrication techniques).

Objective 3. Development of a SAW resonator-based multisensor prototype.
We will develop a SAW resonator-based and a Lamb-wave multisensor for monitoring mechanical parameters (mass, forces, pressure, torque, etc.). We will use MEMs technology in order to be able to define resonating structures (plates, membranes, bridges, etc.) by silicon micromachining. We will investigate various device architectures, providing sensitivity predictions for a given stress configuration.
The applicant has experience in oxide growth on semiconductor substrates, has developed the first effective process for the deposition of epitaxial a-quartz thin films on silicon by soft-chemistry and has already worked with the proposed systems, assuring the feasibility of the project. The development and application of microfabrication methods to develop membranes and cantilever resonators will make the technique progress towards the final application: a piezoelectric sensor configured as a resonator for monitoring mechanical parameters (mass, forces, pressure, torque, etc.). The expected outcomes are technological and scientifically relevant and may lead to industrial patents. Finally, if funded, this project will allow the applicant to establish a new line of research within the hosting lab, in complement with the research activity and expertise in nanotechnologies.