Electrical characterization and modeling of pH and microparticle nanoelectronic sensors

By 2050, the world’s population will have risen to 9.7 billion, with 2 billion over the age of 60. To face this situation the actual healthcare system must be improved and innovated. One way to achieve this is to invest in technology. Already today, advancements in biology, chemistry and medicine are being enabled by devices, tools and instrumentation powered by existing micro- and nanoelectronics; nevertheless the potential of these technologies is still far from being fully developed. In fact, recent years have seen a growing attention toward novel and interdisciplinary research fields at the frontier between life sciences and engineering. One clear example is the area of bioelectronics, which holds the potential to revolutionize, among others, our approach to healthcare. Electronics and the semiconductor industry are sufficiently mature to offer and support a huge variety of solutions, going from the enormous data centers to collect the clinical data of the patients and perform accurate analysis, the ability to provide portable systems equipped with biosensors for point-of-care diagnosis and treatments, and the nanotechnologies and nanobiosensors enabling the so- called personalized medicine and the next-generation of devices for research purposes. Technology innovation and the development of the next-generation bioelectronic sensors require deep understanding of new phenomena and must necessarily pass through a phase of research, design, optimization, and characterization. Accurate numerical and analytical models to predict the transduction performances and the reliability of a new biosensor concept play a role of utmost importance in supporting all of the above. My thesis falls in this realm. In particular, I focused on the modeling and characterization of ion-sensitive field-effect-transistors (ISFETs) made of silicon nanoribbons. The concept of ISFET, developed in the early 1970’s, has re-gained increasing attention in the last decade thanks to its flexibility in sensing different types of analytes and due to its compatibility with the CMOS fabrication process. The research activity was focused in two directions: (i) ISFET characterization with experiments performed in dry and liquid electrolyte environments, and (ii) simulations performed with commercial (Sentaurus TCAD) and in-house developed tools (ENBIOS). Existing simulation tools have been extended and improved to account for surface reactions. We modeled and characterized the pH-sensitivity in DC conditions, and we developed a quasi-3D model for the AC response of nanoribbons to dielectric microbeads in liquid environment. The measurements were performed during a stage at the CLSE laboratory at EPFL (Lausanne, CH), whereas the measurements of the nanoribbons in dry were performed at the University of Udine. Original contributions in this area regard the characterization of signal-to-noise ratio (SNR) in nanoribbon ISFETs and the study of the SNR scaling with the nanoribbon architecture and dimensions. Besides ISFETs, we studied the AC response of electrolyte/insulator/semiconductor samples. The insulator surface was functionalized with a self-assembled-monolayer for the detection of specific molecules. We developed a compact model that is extremely useful to analyze the electrical properties of each part composing the sample and gives useful indications for the realization of a full sensor for the detection of DNA/PNA at the insulator/electrolyte surface. Original contributions in this area regard the development of a compact model capable of detecting different PNA orientations attached on the sensor surface. As a last activity, the thesis describes the publication of two simulation tools on the nanohub.org portal. The tools are based on ENBIOS, include DC and AC the surface reaction models developed during the PhD and represent a useful reference for researchers and scholars interested to explore the potential of the ISFET sensing concept.