Molecular passivation of semiconductor surface for electronic biosensor devices

Recent advances in discovering biomarkers for specific diseases, particularly cancers, have necessitated development of ultra-sensitive biosensors for early diagnosis of critical diseases. To detect small amount of biomarkers, it is imperative to develop efficient transducers that can convert biological interactions into quantifiable signals. Various transduction devices have been demonstrated on the basis of different transduction mechanisms by incorporating a quartz crystal microbalance, quantum dots, nanowires, etc. Among these devices, electrical transducers based on semiconductor electronic devices are considered promising candidates due to their ease of miniaturization, integration into microelectronic circuits, and label-free detection. In this study, development of biosensor platforms for electrical transduction of biological interactions with conventional semiconductor devices is discussed with aim of achieving reliable molecular passivation techniques and discovering a new electrical detection scheme. Detection schemes behind most of previously reported conduction-based biosensors were based on device conductivity changes by net surface charge modulation upon molecular binding events. However, differentiating background noises from molecular effects still remains problematic for clinical tests, particularly when analyte concentration is very low and biosensor device responses are relatively small. As opposed to previous electrical transducers that detected biological interactions by small conductivity modulation, utilization of direct electronic interactions between semiconductor and immobilized bio-molecules is expected to enable different detection principles that are specific to a particular combination of semiconductor and target bio-molecules. In particular, modulation of semiconductor surface states or generation of charge carrier traps due to molecule-semiconductor interactions may lead to more sophisticated detection schemes with enhanced sensitivity and orthogonality. Hence, as development of passivation techniques of Si surface states had enabled commercialization of the current Si technology, finding solutions to molecular passivation of various semiconductor surfaces with organic molecules and control of surface states would be key issues for development of conduction-based biosensors. In order to investigate these issues, various biosensor platforms based on different device schemes are explored, and the observed modulations of device characteristics are analyzed with analytical modeling and 2-D numerical device simulation