Laser Direct Writing of a High-Performance All-Graphene Humidity Sensor Working in a Novel Sensing Mode for Portable Electronics

Abstract

This paper reports a fast and highly sensitive all-graphene humidity sensor working in a novel alternating current (ac) detection mode for the first time, which is capable of sensing humidity on a smartphone for portable electronics. The humidity sensor is based on an interdigitated reduced graphene oxide/graphene oxide/rGO (rGO/GO/rGO) structure patterned by a facile laser direct writing method. It works in an ac sensing mode with a rectangular input voltage wave and measures the output voltage wave instead of conventional resistance, impedance, or capacitance, exhibiting a dramatically enhanced sensitivity by about 45 times compared to the low and unstable response in dc mode. The humidity sensor shows an obvious response to the relative humidity (RH) ranging from RH 6.3% to RH 100%. The response and recovery toward humidity change are almost instantaneous, and the corresponding costed times including humidity rise and decay times are less than 1.9 and 3.9 s, respectively, which are among the best results in the literature. The sensor also exhibits outstanding cycling stability, flexibility, and long-term stability (>1 year), as well as good reproducibility of device preparation. Besides, it can be easily connected to an iPhone and the humidity sensing can be conducted with an oscilloscope application on iOS. What's more, an electronic circuit simulation method was employed to fit the output waves, which can not only explain the sensing mechanism, but also determine the resistance and capacitance of the rGO/GO/rGO structure, agreeing well with the results obtained from the electrochemical measurements. It can be reasonably expected that the approach combining humidity sensing and electronic circuit simulation can be applied in real-time monitoring on a smartphone based on the Internet of things and big data technologies.

Recent Progress in Micro‐Supercapacitor Design, Integration, and Functionalization

“…The current trend for those miniaturized sensing systems is to integrate with MSCs, which can avoid the external power supply, and thus, decrease the overall volume as well as weight. For this motivation, numerous studies on sensor/MSCs self‐powered systems including photodetectors, gas sensors, and strain sensors have been reported . For instance, Kim et al reported on the fabrication of flexible MSC arrays with hybrid electrodes of MWCNT/V 2 O 5 nanowire composites, which powered the SnO 2 NW UV sensor on the same substrate.…”

Review of the Direct Laser Synthesis of Functionalized Graphene and its Application in Sensor Technology

“…Humidity sensors are widely applied in indoor humidity measurements, weather observations, and industrial applications [49 51]. Cai et al [52] fabricated a portable humidity sensor by forming a local rGO electrode using partial laser scribing after dispersing GO on a polyethylene terephthalate substrate. The device was very flexible and did not require additional metal electrodes.…”

“…An oscilloscope cell-phone application is used to confirm that the output wave is produced. Connecting such a sensor to an easily accessible device, such as a cell-phone, demonstrates the applicability of these sensors in a broader sense; i.e., that they can replace conventional large measurement systems and operate in connection with a network [52].…”

Laser Direct Writing of Microstructure on Graphene Oxide/Metal Oxide Hybrid Film

“…Because the GO has a structure with oxygen-containing groups on a graphene plane, a solution process using a GO-dispersed solution can be applied to the manufacturing in printed electronics. In previous papers, we have reported a conductive reduced graphene oxide (rGO) by laser-induced reduction of a GO film and the formation of an rGO/GO/rGO interdigitated microelectrode by laser direct writing [4,5]. The rGO/GO/rGO interdigitated microelectrode can be applied to a humidity sensor based on the changes of C and R parameters by the water molecule adsorption on the GO [4].…”

“…In previous papers, we have reported a conductive reduced graphene oxide (rGO) by laser-induced reduction of a GO film and the formation of an rGO/GO/rGO interdigitated microelectrode by laser direct writing [4,5]. The rGO/GO/rGO interdigitated microelectrode can be applied to a humidity sensor based on the changes of C and R parameters by the water molecule adsorption on the GO [4]. In this paper, we studied the laser direct writing using a GO/CuO nanorods (CuO NRs) hybrid film to functionalize a laser-written rGO microstructure.…”