title: CMOS integration of inkjet-printed graphene for humidity sensing.
abstract: We report on the integration of inkjet-printed graphene with a CMOS micro-electro-mechanical-system (MEMS) microhotplate for humidity sensing. The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer. We formulate inks with different graphene concentrations, which are then deposited through inkjet printing over predefined interdigitated gold electrodes on a CMOS microhotplate. The graphene flakes form a percolating network to render the resultant graphene-PVP thin film conductive, which varies in presence of humidity due to swelling of the hygroscopic PVP host. When the sensors are exposed to relative humidity ranging from 10-80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks. Our sensors show excellent repeatability and stability, over a period of several weeks. The location specific deposition of functional graphene ink onto a low cost CMOS platform has the potential for high volume, economic manufacturing and application as a new generation of miniature, low power humidity sensors for the internet of things.
authors.affiliation: Department of Physics, Indian Institute of Technology, Kharagpur, 721302, India.
authors.forename: S
authors.initials: S
authors.lastname: Santra
authors.affiliation: Cambridge Graphene Centre, University of Cambridge, Cambridge, CB3 0FA, UK.
authors.forename: G
authors.initials: G
authors.lastname: Hu
authors.affiliation: Cambridge Graphene Centre, University of Cambridge, Cambridge, CB3 0FA, UK.
authors.forename: R C T
authors.initials: RC
authors.lastname: Howe
authors.affiliation: Department of Engineering, University of Cambridge, Cambridge, CB3 0FA, UK.
authors.forename: A
authors.initials: A
authors.lastname: De Luca
authors.affiliation: Cambridge CMOS Sensors Ltd., Cambridge, CB4 0DL, UK.
authors.forename: S Z
authors.initials: SZ
authors.lastname: Ali
authors.affiliation: Department of Engineering, University of Cambridge, Cambridge, CB3 0FA, UK.|Cambridge CMOS Sensors Ltd., Cambridge, CB4 0DL, UK.
authors.forename: F
authors.initials: F
authors.lastname: Udrea
authors.affiliation: School of Engineering, University of Warwick, Coventry, CV4 7AL, UK.
authors.forename: J W
authors.initials: JW
authors.lastname: Gardner
authors.affiliation: Department of Physics, Indian Institute of Technology, Kharagpur, 721302, India.
authors.forename: S K
authors.initials: SK
authors.lastname: Ray
authors.affiliation: E &ECE Department, Indian Institute of Technology, Kharagpur, 721302, India.
authors.forename: P K
authors.initials: PK
authors.lastname: Guha
authors.affiliation: Cambridge Graphene Centre, University of Cambridge, Cambridge, CB3 0FA, UK.
authors.forename: T
authors.initials: T
authors.lastname: Hasan