title: Air-Stable Humidity Sensor Using Few-Layer Black Phosphorus.
abstract: As a new family member of two-dimensional layered materials, black phosphorus (BP) has attracted significant attention for chemical sensing applications due to its exceptional electrical, mechanical, and surface properties. However, producing air-stable BP sensors is extremely challenging because BP atomic layers degrade rapidly in ambient conditions. In this study, we explored the humidity sensing properties of BP field-effect transistors fully encapsulated by a 6 nm-thick Al2O3encapsulation layer deposited by atomic layer deposition. The encapsulated BP sensors exhibited superior ambient stability with no noticeable degradation in sensing response after being stored in air for more than a week. Compared with the bare BP devices, the encapsulated ones offered long-term stability with a trade-off in slightly reduced sensitivity. Capacitance-voltage measurement results further reveal that instead of direct charge transfer, the electrostatic gating effect on BP flakes arising from the dipole moment of adsorbed water molecules is the basic mechanism governing the humidity sensing behavior of both bare and encapsulated BP sensors. This work demonstrates a viable approach for achieving air-stable BP-based humidity or chemical sensors for practical applications.
authors.forename: Jinshui
authors.initials: J
authors.lastname: Miao
authors.forename: Le
authors.initials: L
authors.lastname: Cai
authors.forename: Suoming
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Electrical Engineering, Chungnam National University , Daejeon 34134, Korea.
authors.forename: Junghyo
authors.identifier: http://orcid.org/0000-0001-9975-239X
authors.initials: J
authors.lastname: Nah
authors.forename: Junghoon
authors.initials: J
authors.lastname: Yeom
authors.forename: Chuan
authors.identifier: http://orcid.org/0000-0002-5296-0631
authors.initials: C
authors.lastname: Wang
keywords: 2D materials; black phosphorus; encapsulation; humidity sensor; long-term stability