Highly Sensitive Sputtered ZnO:Ga Thin Films Integrated by a Simple Stencil Mask Process on Microsensor Platforms for Sub-ppm Acetaldehyde Detection

Abstract

The integration of a 50-nm-thick layer of an innovative sensitive material on microsensors has been developed based on silicon micro-hotplates. In this study, integration of ZnO:Ga via radio-frequency (RF) sputtering has been successfully combined with a low cost and reliable stencil mask technique to obtain repeatable sensing layers on top of interdigitated electrodes. The variation of the resistance of this n-type Ga-doped ZnO has been measured under sub-ppm traces (500 ppb) of acetaldehyde (C2H4O). Thanks to the microheater designed into a thin membrane, the generation of very rapid temperature variations (from room temperature to 550 °C in 25 ms) is possible, and a rapid cycled pulsed-temperature operating mode can be applied to the sensor. This approach reveals a strong improvement of sensing performances with a huge sensitivity between 10 and 1000, depending on the working pulsed-temperature level.

Fabrication and Characterization of Flexible and Miniaturized Humidity Sensors Using Screen-Printed TiO2 Nanoparticles as Sensitive Layer

“…Examples of flexible sensors integrating additional electronic functions like readout electronics [ 5 , 6 ], thermal compensation systems [ 7 ], and other sensors [ 8 , 9 ] have opened a new route towards multi-functional sensors fabricated on flexible substrate. Despite that, silicon technology is still attractive for the fabrication of sensors due to its mass-production capability, its high degree of miniaturization resulting in high integration density, and, consequently its considerable cost reduction for sensor devices [ 10 , 11 ]. Indeed, as given in the paper of Moore in 1965 [ 12 ]: “With unit cost falling as the number of components per circuit rises”, the cost of one sensor must also decrease as more sensors are put on the substrate.…”

A New Miniaturized Gas Sensor Based on Zener Diode Network Covered by Metal Oxide

“…Zinc oxide is already studied for various applications, and its gas-sensing ability makes it interesting for our work. The choice of gallium-doped zinc oxide comes from a previous work, where its gas-sensing performance was proven in a framework of classical resistive sensors [11].…”

“…Despite the tiny size and the ease of fabrication, due to its smart structure, it takes more than five photolithography processes to pattern all the different layers, including a backside deep reactive ion etching (DRIE) to obtain the suspended round membrane, adding, to the whole system, a mechanical weakness [11]. The heating element was designed to give a homogeneous temperature distribution across the membrane to bring the sensing layer to the working range.…”

“…The weak point of these "resistive" sensors remains their low intrinsic selectivity related to the resistance measurement influenced by many gases (and other influencing factors), regardless of the type of the material used. This drawback can be overcome by the Despite the tiny size and the ease of fabrication, due to its smart structure, it takes more than five photolithography processes to pattern all the different layers, including a backside deep reactive ion etching (DRIE) to obtain the suspended round membrane, adding, to the whole system, a mechanical weakness [11]. The heating element was designed to give a homogeneous temperature distribution across the membrane to bring the sensing layer to the working range.…”

Integration of P-CuO Thin Sputtered Layers onto Microsensor Platforms for Gas Sensing

“…Kneer et al [ 57 ] used similar inkjet-printed CuO nanoparticles deposited on a microsensor and obtained good H 2 S selectivity in the NO 2 , NH 3 and SO 2 atmosphere but with a time pulsation of few minutes. However, there are no articles relating to acetaldehyde detection with a CuO-sensitive layer deposited on a microsensor and operated in pulsed temperature mode, although temperature cycling gives good results for acetaldehyde detection with other sensitive oxides [ 58 ].…”