Heterojunction interface-engineered SnO₂-CuO SAW sensor for room-temperature CO₂ detection with fast response and high selectivity

Abstract

Surface acoustic wave (SAW) sensors demonstrate significant potential in environmental monitoring due to their high sensitivity and fast response capabilities. However, conventional single-component gas-sensitive materials struggle to achieve both wide detection ranges and rapid response simultaneously. This study developed a high-performance composite film through heterostructure engineering to enhance carbon dioxide (CO₂) sensing performance. A bilayer composite gas-sensing functional layer was fabricated by sequentially depositing tin oxide (SnO₂) and copper oxide (CuO) films on a lithium niobate (LiNbO₃) substrate via magnetron sputtering. Experimental results demonstrated that the SnO₂-CuO composite sensor exhibited a CO₂ sensitivity of 11.35 mV/%, representing 4.3-fold and 10.3-fold improvements over pure CuO (2.65 mV/%) and SnO₂ (1.10 mV/%), respectively. The detection range was extended to 0.1-4vol%, with response and recovery times reduced to 9.3 s and 28.9 s at room temperature (25 °C). In addition, the SAW sensor demonstrated excellent repeatability, humidity interference resistance, high selectivity and long-term stability (5.7% signal attenuation over 30 days). Density functional theory (DFT) calculations revealed that the enhanced performance was attributed to heterointerface charge modulation, which increased the adsorption capacity for CO₂ molecules. (Figure presented.)