Microstructure and Electrical Properties of MgAl₂O₄ Thin Films for Humidity Sensing

Abstract

Active elements for humidity sensors based upon MgAI,O, thin films or sintered pellets were investigated. Thin films were deposited on Si/SiO, substrates by radiofrequency (rf) sputtering. Sintered MgAI20, 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 MgAI,O,. Sintered MgAI,O, is crystalline, while it is disordered in thin-film form. The presence of two different components of the Al 2p 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. MgAI,O, 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 MgAI,O, pellets and thin films were correlated with their different microstructures.

Self-Organizing Growth of MgAl2O4 Based Heterostructural Nanochains

“…32 In this paper, we report successful preparation of MgAl 2 O 4 based Mg-Al-Si oxide heterostructural nanochains via self-organizing growth using an easily controlled chemical vapor deposition method. These oxide based nanochains are expected to find their potential applications in developing tunable one-dimensional humidity sensors, 30 solid-state lasers, 31 catalysts or catalyst supports, 32 and other nanodevices.…”

“…Recently, some research work has been done on one-dimensional spinel oxides. [24][25][26][27][28][29] As a typical spinel oxide, some intriguing properties of MgAl 2 O 4 have been reported, such as distinct electrical properties, 30 excellent luminescence, 31 and high hydrothermal stability. 32 In this paper, we report successful preparation of MgAl 2 O 4 based Mg-Al-Si oxide heterostructural nanochains via self-organizing growth using an easily controlled chemical vapor deposition method.…”

Grabbing pebbles out of my shoes: Thoughts of a grumpy old researcher on publishing research

“…It took a lot of time and discussions to convince my professor to submit a paper to the Journal of the American Ceramic Society, but when fi nally I did, it was accepted and published. 1 On another paper, 2 Professor Mario Arpaia, who unfortunately prematurely passed away many years ago, told me that its publication happened only thanks to my "capa tosta" (stubbornness). I submitted another paper to Corrosion against the opinions of my seniors, and six months later, I received a small card with the response: Accept as is!…”

Identification of Humidity Sensing Mechanism in MgAl2O4 by Impedance Spectroscopy as Function of Relative Humidity

“…The main characteristics of humidity sensors are sensitivity, reproducibility and response time. In the case of porous ceramic humidity sensors, the microstructure developed during the sintering process, specifically the total porosity and pore size distribution, is responsible for these characteristics 1,13,14 . Microstructures with specific characteristics can be obtained by adding dopants that control the sintering mechanisms [15][16][17] .…”