Sensing layer combination of vertically aligned ZnO nanorods and graphene oxide for ultrahigh sensitivity IDE capacitive humidity sensor

Abstract

An interdigitated electrode (IDE) capacitive humidity sensor fabricated on a silicon substrate was used to investigate sensing materials, which proved to be an ultrahigh-sensitivity humidity sensor. A sensing layer combination (SLC) between vertically aligned ZnO nanorods and optimal graphene oxide (GO) was prepared on the device and was tested as a humidity sensor. X-ray diffractometry (XRD) exhibited crystallized wurtzite structure of ZnO nanorods and transmission electron microscope (TEM) shown perfectly indexed hexagonal wurtzite ZnO structure dots position correspondence. A scanning electron microscope (SEM) was used to analyze ZnO nanorods/GO morphologies. Furthermore, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly exhibited GO presence and hydrophilic functional groups (carboxyl, epoxy, and hydroxyl), respectively. The SLC prominently demonstrated ultrahigh sensitivity (up to 196.95% or 1.97 times from commercial sensor; HS1101, Humirel) and linear responses behavior with 0.96 for coefficient of determination. The device sensitivity obviously improved as steps of 40, 50, 60, 70, 80, and 90% RH at values of 1.09, 1.41, 1.51, 1.65, 1.80, and 1.91 times, respectively. The device also exhibited fast response (25 s) and short recovery times (17 s). Its hysteresis (6.58%) manifestly improved to 1.84 times. Moreover, repeatability and long-term ability of the device demonstrated high accuracy (range ±0.37pF) and durability.

Performance of the highly sensitive humidity sensor constructed with nanofibrillated cellulose/graphene oxide/polydimethylsiloxane aerogel via freeze drying

“…6d , three strong peaks can be observed in the O 1s spectrum, located at 531.2 eV, 532.3 eV and 533.4 eV, respectively, which are related to C O, C–O and O–C O groups. 31 The aerogel has similar groups to other existed GO composite humidity sensitive material, which had been proved that it has certain humidity sensitive characteristics. 24,25 …”

“…Appropriate amount of GO promotes the humidity sensitivity of the sensor. 31 The sensitivity of sensor increased with raising the content of GO from 10 wt% to 30 wt%. The addition of 30 wt% GO gained a higher capacitance output value and sensitivity.…”

“…6d, three strong peaks can be observed in the O 1s spectrum, located at 531.2 eV, 532.3 eV and 533.4 eV, respectively, which are related to C]O, C-O and O-C]O groups. 31 The aerogel has similar groups to other existed GO composite humidity sensitive material, which had been proved that it has certain humidity sensitive characteristics. 24,25 Density and exibility analysis It is found from Table 2 that the density of NFC/GO/PDMS aerogel is as small as 5.23 kg m À3 , which indicates that the aerogel has high porosity and specic surface area.…”

“…However, a single sensing material still has certain defects in the response performance of the sensor in the high relative humidity range. 31 Our work proposed to use ultrasonic dispersion and vacuum freeze drying method to install NFC/GO/PDMS aerogel with abundant three-dimensional porous structure on the flexible interdigital electrode to prepare a new kind of NFC/GO/PDMS humidity sensor. The use of NFC and GO with numbers of hydrophilic groups attracting more water molecules can increase the response of sensor.…”

Numerical Study of a Capacitive Graphene Oxide Humidity Sensor with Etched Configuration

“…ΔRH denotes the difference between "50" and "10" values, which are the highest and lowest RH values taken to show the average sensitivity. 7,12,19,21 2.1. Dimension Effect on the Sensor Performance.…”