Our work focuses on the design and rigorous evaluation of two novel designs for semiconducting metal oxide (SMO) gas sensors with different shapes and sizes, in order to assess the most efficient layout geometry in terms of power consumption, membrane stability, and temperature distribution. The aim of this study is to provide two designs, one to be used for a thin sensing film and the other to be applied with a nanowires sensing layer. Both designs implement innovative aspects, allowing for an improvement in state-of-the-art sensors’ selectivity and power consumption, which make the product suitable for use on a wide variety of applications. To further support the simulation results, an analytical model based on a Cauer network is presented for estimating the power consumption of the device. We demonstrate the ability of SMO sensors to operate at 300°C with high uniform temperature over the sensing material and ultra low power consumption of roughly 8mW. In addition, a microheater array design is presented, which is able to heat two active sensing layers to 270°C; and 350°C simultaneously in 40μs. Both designs are analyzed for stability and it was found that the stress generated in the membranes and the resulting deformation is minimal, improving the device stability and reliability.

The growing demand for the integration of functionalities on a single device is peaking with the rise of IoT. We are near to having multiple sensors in portable and wearable technologies, made possible through integration of sensor fabrication with mature CMOS manufacturing. In this paper we address semiconductor metal oxide sensors, which have the potential to become a universal sensor since they can be used in many emerging applications. This review concentrates on the gas sensing capabilities of the sensor and summarizes achievements in modeling relevant materials and processes for these emerging devices. Recent advances in sensor fabrication and the modeling thereof are further discussed, followed by a description of the essential electro-thermal-mechanical analyses, employed to estimate the devices' mechanical reliability. We further address advances made in understanding the sensing layer, which can be modeled similar to a transistor, where instead of a gate contact, the ionosorped gas ions create a surface potential, changing the film's conduction. Due to the intricate nature of the porous sensing films and the reception-transduction mechanism, many added complexities must be addressed. The importance of a thorough understanding of the electro-thermal-mechanical problem and how it links to the operation of the sensing film is thereby highlighted.

Semiconducting metal oxide (SMO) gas sensors were designed, fabricated, and characterized in terms of their sensing capability and the thermo-mechanical behavior of the micro-hotplate. The sensors demonstrate high sensitivity at low concentrations of volatile organic compounds (VOCs) at a low power consumption of 10.5 mW. In addition, the sensors realize fast response and recovery times of 20 s and 2.3 min, respectively. To further improve the baseline stability and sensing response characteristics at low power consumption, a novel sensor is conceived of and proposed. Tantalum aluminum (TaAl) is used as a microheater, whereas Pt-doped SnO2 is used as a thin film sensing layer. Both layers were deposited on top of a porous silicon nitride membrane. In this paper, two designs are characterized by simulations and experimental measurements, and the results are comparatively reported. Simultaneously, the impact of a heat pulsing mode and rubber smartphone cases on the sensing performance of the gas sensor are highlighted.

The microheater is an important part of a semiconducting metal oxide gas sensor, as its primary function is to heat up the sensitive layer to a desired temperature. The operating temperature of the sensor depends on the sensitive material used and the species of the target gases. Therefore, an accurate extraction of the sensor active area temperature as a function of the applied power is critical for device characterization. These measurements are experimentally challenging due to the extremely small sensing surface area, down to a few tens of μm², resulting in the need to develop new measurement approaches. In this paper, quantitative testing methods based on platinum and chrome silicon (CrSi) resistance thermometry, as well as a qualitative testing method (light glow) have been carried out to measure the power consumption of two different devices. CrSi has been used as a temperature sensor due to its ability to detect temperatures above 450 °C by acting as a phase-change material. For accurate measurements of temperature distribution, the presented gas sensors are equipped with three configurations of resistive temperature detectors at different locations. To further analyze a sample closed-membrane sensor, finite-element simulations were performed and an analytical model was designed and compared with experimentals. [2017-0228]

Semiconducting metal oxide (SMO) gas sensors, dedicated to wearable devices were designed, fabricated, and characterized in terms of power consumption, thermal distribution, and sensing capability. The sensors demonstrate a sensitivity down to ppb-level VOC concentrations at a low power consumption of 10.5 mW. To further enhance the baseline stability and sensing response characteristics at low power consumption, a new sensor structure is proposed. The design implements novel aspects in terms of fabrication and microheater geometry, leading to improved sensor performance which enables new applications for SMO gas sensors. In this work, two designs were analyzed using experimental characterization and simulation. The results of the analyses of the two sensors are comparatively reported.