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

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 O^2- 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 O^2- 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.