Junkai Zhang

Few-layer molybdenum disulfide (MoS2) has attracted great attention because of its novel electrical and optoelectrical properties for devices. In this paper, we perform a systematic study on evolution of electrical performance of few-layer MoS2 field-effect transistors (FETs) under microwave annealing. As a result, obvious improvements on electrical properties are achieved for the sample annealed in N2 ambience between 420 W and 840 W: the on/off current ratio of ~8.34×108 and the hysteresis of 2.1 V, which are ~150 times higher and ~2.1 times smaller compared with that of as fabricated MoS2 FET, respectively. The proposed technique provides a new method to approach high-performance few-layer MoS2 FETs with minimized parasitic resistances..

It has been known that the slow response of ion-sensitive field-effect-transistors (ISFETs), with tremendous challenges on meeting the requirements of the accuracy and long-term stability, handicaps extensive application of ISFET sensors. In this paper, dual-mechanism slow site-response (DSSR) model, combining enriched buried sites theory and the mechanism of specific adsorption activity (SAA) of effective sites, is proposed to systematically understand the slow response characteristics of ISFETs during a test of pH variation. The SAA variation occurs during the whole slow response process, while the effects of buried sites dominate only at the short-term slow response stage. Experiments based on extended-gate ion-sensitive field-effect-transistors using both aluminum oxide and silicon nitride as sensing layer were carried out. It is found that the DSSR model can excellently explain the slow response characteristics of the measured ISFETs. Furthermore, the slow response characteristics of ISFETs with silicon nitride are revealed to be superior to that of ISFETs with aluminum oxide in the slow response performance.

The effects of UV-ozone (UVO) treatment on the sensing behaviours of extended-gate field-effect transistors (EGFETs) that use Al₂O₃ as the sensing film have been investigated. The Al₂O₃ sensing films are UVO-treated with various duration times and the corresponding EGFET sensing behaviours, such as sensitivity, hysteresis, and long-term stability, are electrically evaluated under various measurement conditions. Physical analysis is also performed to characterize the surface conditions of the UVO-treated sensing films using X-ray photoelectron spectroscopy and atomic force microscopy. It is found that UVO treatment effectively reduces the buried sites in the Al₂O₃ sensing film and subsequently results in reduced hysteresis and improved long-term stability of EGFET. Meanwhile, the observed slightly smoother Al₂O₃ film surface post UVO treatment corresponds to decreased surface sites and slightly reduced pH sensitivity of the Al₂O₃ film. The sensitivity degradation is found to be monotonically correlated with the UVO treatment time. A treatment time of 10 min is found to yield an excellent performance trade-off: clearly improved long-term stability and reduced hysteresis at the cost of negligible sensitivity reduction. These results suggest that UVO treatment is a simple and facile method to improve the overall sensing performance of the EGFETs with an Al₂O₃ sensing film.

In this paper, capacitive-type humidity sensors were prepared by sequentially drop-coating the aqueous suspensions of zinc oxide (ZnO) nanopowders and polyvinyl pyrrolidone–reduced graphene oxide (PVP-RGO) nanocomposites onto interdigitated electrodes. Significant improvements in both sensitivity and linearity were achieved for the ZnO/PVP-RGO sensors compared with the PVP-RGO/ZnO, PVP-RGO, and ZnO counterparts. Moreover, the produced ZnO/PVP-RGO sensors exhibited rather small hysteresis, fast response-recovery time, and long-term stability. Based on morphological and structural analyses, it can be inferred that the excellent humidity sensing properties of the ZnO/PVP-RGO sensors may be attributed to the high surface-to-volume ratio of the multilayer structure and the supporting roles of the PVP-RGO nanocomposites. The results in this work hence provide adequate guidelines for designing high-performance humidity sensors that make use of the multilayer structure of semiconductor oxide materials and PVP-RGO nanocomposites.