Novel approaches for microscale sensing using silicon and graphene based devices

Recent advances in nanofabrication technologies and micro-electromechanical systems (MEMS) have attracted significant attention to miniaturized sensors. The combination of small sizes and high sensitivities with integrated wireless transmission capabilities shows great promise in a variety of applications including implantable biomedical devices, electronic pills or general body area networks. However, for all these emerging application areas, which require ever shrinking device sizes, novel sensing approaches are often necessary to retain device functionality. There are different types of sensing methodologies and materials available, each with their own advantages and limitations; as such method selection has to be dependent on the application, required functionality, as well as, other limiting conditions such as the operational environment. Hence, it is challenging to acquire one principal method or material that can universally be applied for a wide range of applications. Potentially, improvements can be achieved through novel sensing approaches, or utilizing a new class of materials to address specific applications. This thesis explores these two approaches on a range of applications which will potentially have widespread appeal and open multiple pathways for further research in the field. Firstly, microfabricated Si based devices are developed which utilize novel approaches to improve sensor performance while decreasing the physical size. This has been realized in three applications areas: (1) a variable inductance displacement sensor, (2) a force sensor using feedback control to nullify displacements and (3) a fringing field capacitive pH sensor. The second part of the thesis focuses solely on using material properties of novel graphene based nanostructures (three dimensional soft graphene monoliths and casted graphene oxide films). Importantly, all complex fabrication procedures and detection circuitry are avoided. Instead, novel features of the materials itself which have been used to measure of (1) vibration and (2) strain. This approach offers simpler designs and relatively cheaper fabrication, as well as having the potential to synergize well with flexible substrates.