The objective of this research is to develop fundamental understanding on how the performance of nanoscale field effect transistor biosensors depends on device geometrical sizes at different physical conditions. The approach is to numerically investigate device scaling behaviors at various physical conditions by using a random resistor network model and experimentally test these scaling laws at different field effect strengths by using Si-based devices as a model system. Intellectual Merit: The outcome of this research will answer the fundamentally intriguing and technologically important question on whether and how the sensitivity and detection limits of field effect biosensors depend on their geometrical dimensions and relevant physical parameters. The project is transformative in terms that scaling laws for field effect biosensors as critical design guidelines will enable tailoring the sensitivity and detection limits in accordance with target analyte concentrations, and enable design of devices with ultra-low detection limits. Broader Impacts: Ultra-sensitive biosensors can find various applications from food safety, homeland security to disease diagnostics for human health care. Graduate and undergraduate students will be trained in this interdisciplinary project on device and computational physics, semiconductor nanostructure fabrication and characterization, and surface and interface biochemistry. Special efforts will be made to recruit female and underrepresented minority students for participation. Research discoveries from this project will be incorporated into the courses developed by the principle investigators. Outreach activities include school visits, training of high school senior students, and participation of NSF GK-12 Program.
The objective of this research is to develop fundamental understanding of how the performance (i.e., sensitivity and detection limit) of nanoscale field effect transistor (nanoFET) biosensors depends on device geometrical sizes at different physical conditions such as ion concentration in solution, control gate voltage and doping concentration of the semiconductor materials. We employed Si and GaN based nanoFETs as model systems and have developed top-down nanofabrication techniques for device fabrication because of their good control on device sizes. We performed theoretical analysis by extending the random resistor network model to include more realistic experimental situations. We also compared the numerical simulation results of 3-D nano-FET structures with an analytical model. The key issues that have been addressed in this project include: (1) Tuning the field effect strength by varying the Debye screening length, the distance between binding molecules and device surface, and the semiconductor doping concentration. (2) Scaling law: measuring the sensitivity of nanoFET sensors as a function of device sizes/aspect ratio at different field effect strengths; measuring the binding kinetics as a function of device sizes/aspect ratios. (3) Multiscale theoretical investigations by both 3-D numerical simulations and analytical model modeling of nanoFET sensors, to extend random resistor models to include different screening lengths. (4) Design and explore nanoFETs for single molecule sensing. We showed that planar AlGaN/GaN heterojunction nanoFET sensors have higher a signal-to-noise ratio than reported Si nanowire and carbon nanotube FET sensors. Based on the above theoretical and experiment results on bioFET scaling rules, we demonstrated devices with enhanced sensitivity of 16 aM (attomolar) for protein detection or 5 protein molecules in the sensing area. To the best of our knowledge, this is the highest sensitivity ever reported on a planar field effect-based biosensor. The research results and findings have been published in high impact journals and presented in leading international conferences. The key technology developed from this project is licensed to a university spinoff company for commercialization. Two Ph.D students (one underrepresentative) trained in this project have graduated and received their Ph.D degrees. A number of undergraduate student researchers including one underrepresentative obtained research experienced under REU supplements. The outreach activities include four sessions of nanobiotechnology summer camps for high school senior students, hosting of two high school seniors as summer interns in the laboratory working with graduate and undergraduate researchers.
