UC San Diego

Since the recent development of Indium-Gallium-Zinc-Oxide (IGZO) thin-film transistor (TFT), oxide semiconductors have received considerable attention and are widely used as a TFT backplane for the state-of-art active-matrix flat panel display. However, the device application of oxide-TFTs is limited to unipolar devices due to the absence of high-performance p-channel oxide TFTs. This limitation poses a significant challenge in advancing oxide device technology, particularly in realizing complementary metal-oxide semiconductor (CMOS) inverter circuits.Tin monoxide (SnO) emerges as a promising oxide semiconductor to develop high-performance p-channel oxide-TFTs due to relatively good hole mobility and low-temperature processability below 300 °C. But their device performances are still largely behind n-channel oxide TFTs (e.g., IGZO, ZnO) because of high-density subgap defects (1020 cm−3) originated from oxygen vacancy (Vo). By incorporating hydrogen annealing after pulse laser deposition (PLD), Vo induced hole traps in SnO were effectively reduced by forming Sn-H bonds, improving TFT mobility to ~1.8 cm2/Vs and Ion/Ioff ratio to ~105. In addition, the subgap defects were further suppressed by adding back-channel passivation layer, allowing SnO-TFTs to exhibit ambipolar behavior by alleviating the fermi-level pinning near valence band (VB) defects. Lead (Pb2+) exposure is a serious health concern that possesses detrimental effects on public health, causing irreversible damage to minors. Both conventional and home kit detection methods face limitations either high cost or poor reliability and limit of detection (LoD). In addition to studies on oxide semiconductors, I will discuss the label-free graphene field-effect transistor (GFET) based aptamer sensor (aptasensor) specific to Pb2+ sensing. The surface of chemical vapor deposition (CVD) synthesized graphene is functionalized with Pb2+ specific aptamer (Ap), a single-stranded DNA oligonucleotide, serving as a receptor probe binding to linker molecules on graphene. The binding of the target Pb2+ to the Ap is transduced into modulations of the electrical current through graphene FET. The theoretical LoD of GFET aptasensor is discussed based on thermodynamic prediction of probe – linker – channel surface binding energies. The surface density of Ap on graphene is optimized by monitoring minimization of capacitance via electrochemical impedance spectroscopy (EIS) to reach uniform Ap distribution, avoiding steric hinderance due to Ap clustering. The record sensor sensitivity was demonstrated with LoD of ~ 7.0 fM, reaching the LoD predicted from the theoretical thermodynamic prediction.