Preparation, morphology, and gas-sensing behavior of Cr/sub 2-x/Ti/sub x/O/sub 3+z/ thin films on standard silicon wafers

Abstract

The effect of humidity on chromium titanium oxide (Cr/sub 2-x/Ti/sub x/O/sub 3+z/, CTO), on both baseline resistance and sensitivity, is small compared to SnO/sub 2/. This has been the key to development of thick-film sensors based on CTO, for detection of carbon monoxide and ammonia in synthetic air. Thin-film structures on silicon substrates offer the possibility to use fabricating, bonding and housing equipment and, hence, a low cost gas sensor production is possible. CTO thin-film sensors on silicon substrates use conventional photolithography, sputtering and evaporation techniques. A Ta/Pt resistance layer (25/200- nm thick) for heating the device to its operating temperature and interdigital electrodes are evaporated and structured on a silicon substrate which is covered by a 1- mu m SiO/sub 2/ insulating layer. The polycrystalline p-type CTO is deposited onto the electrodes by oxidizing reactive sputtering or evaporation of Cr/Ti-sandwich structures. The resulting sensors were characterized by means of energy dispersive X-ray analysis, secondary electron microscopy, and X-ray diffraction pattern. Also, gas responses toward NO/sub 2/, NH/sub 3/, CO and CH/sub 4/, and different humidity, were investigated

Synthesis, characterization and thermal expansion of Cr2−xTixO3+δ

“…Titanium-substituted chromium oxides (CTO) have been developed successfully as gas-sensitive resistors at elevated temperatures for the detection of combustible and toxic gases [2][3][4][5][6]. In recent years the study of Cr 2 O 3 thin films has become a topic of great interest because of their practical applications in fields like the detection of hazardous gases [7][8][9]. When the films are deposited at substrate temperature Ts < 550 • C they grow with an amorphous structure, and those deposited at Ts ≥ 550 • C grow in a crystalline structure that depends on the x-values in Cr 2−x Ti x O 3+ı .…”

C ‐plane chromia on c ‐plane sapphire

“…5), which may be important in practice. For we could not find any literature hint about testing epitaxial chromia in sensor application conditions, we will compare our results with the ones obtained by other authors on a related material-nonepitaxial uncoated chromia-titania thin films [30][31][32]. In the cited works, the measuring temperature was 400 ºC (it is to be supposed that the temperature lowering progressively decreased the response).…”

Preparation, material analysis, and morphology of Cr2 − xTixO3 + z for gas sensors

“…For these measurements CTO was printed on Si/SiO 2 substrates with platinum heater and interdigital electrodes as describes in Ref. [10].…”

“…The material analyses focus on the crystallite structure and size distribution of the CTO particles, two crucial parameters for the subsequent deposition and sensing behavior. The crystallite structure is commonly determined by XRD [7,8,10]. The grain size can by calculated from the XRD measurements using the Scherrer formula.…”