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Microstructure and Electrical Properties of MgAl 2 O 4 Thin Films for Humidity Sensing
Author(s) -
Gusmano Gualtiero,
Montesperelli Giampiero,
Traversa Enrico,
Mattogno Giulia
Publication year - 1993
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1993.tb03669.x
Subject(s) - thin film , materials science , microstructure , x ray photoelectron spectroscopy , pellets , scanning electron microscope , analytical chemistry (journal) , composite material , substrate (aquarium) , humidity , sputtering , mineralogy , chemical engineering , nanotechnology , chemistry , oceanography , chromatography , geology , engineering , physics , thermodynamics
Active elements for humidity sensors based upon MgAl 2 O 4 thin films or sintered pellets were investigated. Thin films were deposited on Si/SiO 2 substrates by radiofrequency (rf) sputtering. Sintered MgAl 2 O 4 pellets were prepared by traditional ceramic processing. Scanning electron microscopy (SEM) analysis showed that the thin films were rather dense and homogeneous, made up of clustered particles of about 20–30 nm, while the pellets showed a wide pore‐size distribution. X‐ray photoelectron spectroscopy (XPS) demonstrated that the thin films have a stoichiometry close to that of MgAl 2 O 4 . Sintered MgAl 2 O 4 is crystalline, while it is disordered in thin‐film form. The presence of two different components of the Al 2 p peaks was correlated with the structural difference between pellets and thin films. The relationship between good film–substrate adhesive properties and the chemical composition at the interface was studied. The electrical properties of the sensing elements were studied at 40°C in environments at different relative humidity (RH) values between 2% and 95%, using ac impedance spectroscopy. MgAl 2 O 4 thin films showed interesting characteristics in terms of their use in humidity‐measurement devices. Resistance versus RH sensitivity values showed variations as high as 4 orders of magnitude in the RH range tested for thin films, and 5 orders of magnitude for pellets. The differences in the electrical behavior of MgAl 2 O 4 pellets and thin films were correlated with their different microstructures.