Abstract
The increasing scaling demand of silicon integrated devices comprising specific functionalities, has lead the industry and mainly the academy to propose new alternatives. The challenges include to shrink integrated devices as well as preserving important features such as: fast operational capacity, high sensitivity and thin oscillators with higher resonance frequencies. Owing to address the devices scalability, there is a constant development of new materials, as for example:, 2D: graphene sheets, 1D: oxide nanowires and carbon nanotubes, 0D: quantum boxes). Oxides take on considerable importance in this context of diversification as they cover a wide spectrum of physical properties of interest for future applications.α-quartz is widely employed in the manufacture of oscillators and transducers in all electronic devices, therefore making it a very important piezoelectric material for the industry. This oxide has a high-quality factor, excellent chemical and thermal stability, features that it into a high candidate for selective sensing devices. The nanostructuring and on-chip integration of α-quartz would allow for a device with faster operation, higher frequency filtering and better detection and sensitivity levels, thus meeting the challenges of the current market.This thesis is thus part of the dynamics of diversification of the silicon industry, known as “more than Moore” and aims to integrate new functionalities, with low cost, on a microelectronic platform. Thereby, an innovative piezoelectric micro-sensor based on alpha-quartz was realised through monolithic integration, this piezoelectric structures is grown on the top of a silicon nanostructured thin layer.As a result, two microfabrication processes were implemented resulting in two microsensors with different morphologies, a cantilever and a membrane. This work has showed the possibility of combining clean room microfabrication techniques with new methods of manufacturing functional oxides epitaxial with the sol-gel chemical process. These two sensors were then characterised in order to analyse their performance by studying the structural, piezoelectric and electromechanical properties. X-ray diffraction was used to qualify the crystalline quality of the material after the various micro-fabrication stages. Direct piezoelectric effect microscopy (DPFM) proved the piezoelectric aspect of the epitaxial α-quartz layer. Using an atomic force microscope (AFM), a mass detection sensitivity of 100 ng.Hz-1 was determined with the cantilever. Also, the membrane was tested as a photo acoustic sensor by achieving a detection threshold of 36 ppm CH4.These two α-quartz piezoelectric microsensors developed during this thesis address the challenge of bridging the gap between soft chemistry and micro-machining techniques usually performed in clean rooms. This breakthrough opens the way to a new family of more sensitive, scalable, low-cost, non-toxic piezoelectric sensors that can be integrated into microelectronic systems offering a wide range of applications in the fields of biology, biomedicine, and photonics/photoacoustics.