Double-Step Modulation of the Pulse-Driven Mode for a High-Performance SnO₂ Micro Gas Sensor: Designing the Particle Surface via a Rapid Preheating Process

Abstract

To improve the sensing properties toward volatile organic compound gases, a preheating process was introduced in a miniature pulse-driven semiconductor gas sensor, using SnO2 nanoparticles. The miniature sensor went through a short preheating span at a high temperature before being cooled and then experienced a measurement span under heating; this is the double-pulse-driven mode. This operating profile resulted in the modification of the surface conditions of naked SnO2 nanoparticles to facilitate the adsorption of O2– and ethanol-based adsorbates. Temperature-programmed reaction measurement results show that ethanol gas was adsorbed onto the SnO2 surface at 30 °C, and the adsorption amount of ethanol and its byproducts was increased after ethanol exposure at high temperatures followed by cooling. The electrical resistance of the sensor in synthetic air increased as the preheating temperature increased. The sensor responses, S i and S e, to 1 ppm ethanol at 250 °C were enhanced by introducing the preheating process; S i values at 250 °C with and without preheating at 300 °C are 40 and 15, respectively. The obtained improvements were attributed to an increase in O2– adsorption onto the SnO2 surface during the preheating phase. During the cooling phases, the adsorption of ethanol-based molecules onto the SnO2 surface and their condensation in the sensing layer contributed to the enhanced performance. In addition, the double-pulse-driven mode improves the recovery speed in the electrical resistance after gas detection. These improvements made in the sensing properties of the double-pulse-driven semiconductor gas sensors provide desirable advantages for healthcare and medical devices.

One-Trillionth Level Toluene Detection Using a Dual-Designed Semiconductor Gas Sensor: Material and Sensor-Driven Designs

“…R a clearly increased with the increasing preheating temperature, and this trend corresponds to the previous report using SnO 2 . 13 Such an increase in the electrical resistance was likely caused by the change of O − into O 2− . In addition, in the case of the Pd-SnO 2 CNPs, the p−n junction between the n-type SnO 2 and p-type PdO particles enhanced R a because the carrier concentration of SnO 2 was reduced.…”

“…Here, S i was impacted by a combination of the conventional gas sensing reaction, which is the combustion reaction using atmospheric toluene and the combustion of adsorbed toluene on the particle surface. 13,14 Both the increasing O 2− concentration and the high oxidation state of Pd certainly enhanced the conventional response. However, the effect of the preheating process on the toluene adsorption onto the to O − likely increases the slope.…”

“…Figure c shows the preheating temperature dependence of R a and R g,i in the 7.9 ppb toluene/air measured at 250 °C. R a clearly increased with the increasing preheating temperature, and this trend corresponds to the previous report using SnO 2 . Such an increase in the electrical resistance was likely caused by the change of O – into O 2– .…”

“…By introducing the preheating process before heater-off and heater-on for the measurement phases, which is called the double-pulse-driven mode, the particle surface becomes bare and changes the adsorbed oxygen species from O − to O response. 13 In addition, transforming O − into O 2− enhanced the sensor response because of the increased electron consumption amount in each combustion reaction. Therefore, combining the material designs using Pd-SnO 2 CNPs and the double-pulse-driven mode promises further enhancement of the sensor response to toluene gas, which can be expected to lower the detection limit toward the ppt level.…”

“…By introducing the preheating process before heater-off and heater-on for the measurement phases, which is called the double-pulse-driven mode, the particle surface becomes bare and changes the adsorbed oxygen species from O – to O 2– . According to the ethanol temperature-programmed reaction measurement, the amount of adsorbed ethanol on the SnO 2 surface increased by opening the bare surface, and it increases the sensor response . In addition, transforming O – into O 2– enhanced the sensor response because of the increased electron consumption amount in each combustion reaction.…”