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

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.