Tungsten trioxide ( \(\text{WO}_3\) ) thin films were prepared via spray pyrolysis technique with various deposition cycles from 100 to 500 cycles. The effect of deposition cycle number on the structural, morphological, and sensing characteristics of the thin films was systematically examined to determine optimal sensing performance. X-ray diffraction (XRD) confirmed the monoclinic phase of \(\text{WO}_3\) , with improved crystallinity at higher cycles. Surface morphology, examined by SEM analysis revealed uniform surface morphology with well-developed grains, and the average grain sizes estimated from SEM micrographs were 70–125 nm, 80–150 nm and 100–150 for the films deposited at 300, 400 and 500, respectively. XPS analysis confirmed the \(\text{W}^{6+}\) oxidation state and high purity of the deposited thin films. BET analysis for selected cycles (300, 400 and 500) indicated a direct correlation between surface area and cycle number. These structural and surface features, supported by XPS data, contributed to enhanced gas sensing performance. The material showed its highest sensitivity to acetone gas, with 500 deposition cycles. Operating at 350 °C, the sensor showed a strong performance with quick sensing behaviour, achieving a response time of 18 s and recovering in just 19 s. The potential of \(\text{WO}_3\) thin film controlled by deposition cycles for high sensitive and specific medical gas/vapour sensor is demonstrated in this work.
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