Performance and Stress Analysis of Metal Oxide Films for CMOS-Integrated Gas Sensors

Abstract

The integration of gas sensor components into smart phones, tablets and wrist watches will revolutionize the environmental health and safety industry by providing individuals the ability to detect harmful chemicals and pollutants in the environment using always-on hand-held or wearable devices. Metal oxide gas sensors rely on changes in their electrical conductance due to the interaction of the oxide with a surrounding gas. These sensors have been extensively studied in the hopes that they will provide full gas sensing functionality with CMOS integrability. The performance of several metal oxide materials, such as tin oxide (SnO2), zinc oxide (ZnO), indium oxide (In2O3) and indium-tin-oxide (ITO), are studied for the detection of various harmful or toxic cases. Due to the need for these films to be heated to temperatures between 250 °C and 550 °C during operation in order to increase their sensing functionality, a considerable degradation of the film can result. The stress generation during thin film deposition and the thermo-mechanical stress that arises during post-deposition cooling is analyzed through simulations. A tin oxide thin film is deposited using the efficient and economical spray pyrolysis technique, which involves three steps: the atomization of the precursor solution, the transport of the aerosol droplets towards the wafer and the decomposition of the precursor at or near the substrate resulting in film growth. The details of this technique and a simulation methodology are presented. The dependence of the deposition technique on the sensor performance is also discussed.

Thickness and annealing effects on thermally evaporated InZnO thin films for gas sensors and blue, green and yellow emissive optical devices

“…Thus results in an overall decrease or increase in the metal oxide resistance [95]. According to Filipovic et al In 2 O 3 and ZnO based metal oxide materials can be used as gas sensors, when heated to temperatures between 250 C and 550 C [95]. But present investigation revealed that InZnO materials exhibited gas sensor response even at room temperature.…”

“…At higher temperatures, oxygen is adsorbed at the metal oxide surface by trapping electrons from the bulk material. Thus results in an overall decrease or increase in the metal oxide resistance [95]. According to Filipovic et al In 2 O 3 and ZnO based metal oxide materials can be used as gas sensors, when heated to temperatures between 250 C and 550 C [95].…”

Ultra-low NO2 detection by gamma WO3 synthesized by Reactive Spray Deposition Technology

“…5 (c) it can be inferred that the WO 3 film surface is rough and porous with the formation of some agglomerates around 5-10 m wide. Various open pores could be seen which is advantageous for the diffusion of gases in the bulk of the film [55]. The total WO 3 deposition area on the gold electrodes was 97.5 mm 2 .…”

Processing of integrated gas sensor devices

“…At increased temperatures, oxygen is adsorbed at the metal oxide surface by trapping electrons from the bulk material [16]. The result is the formation of a depletion layer at the surface and an overall decrease or increase in the metal oxide resistance, depending on whether the material is n-type or p-type, respectively.…”