Thin plasma-polymerized layers of hexamethyldisiloxane for humidity sensor development

• Published in: Thin solid films 2009-06, Vol.517 (15), p.4455-4460
• Main Authors: Guermat, N., Bellel, A., Sahli, S., Segui, Y., Raynaud, P.
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Electric discharges; Exact sciences and technology; Fourier transform infrared spectroscopy; Glow; corona; Humidity; Ion and electron beam-assisted deposition; ion plating; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Organosilicon; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma applications; Plasma deposition; Plasma-based ion implantation and deposition; Sensor; Thin films
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2009.01.084

The response of resistive-type sensors based on thin hexamethyldisiloxane layers to relative humidity (RH) was evaluated. Humidity sensitive layers were plasma polymerized at low frequency glow discharge using a capacitively coupled parallel plate reactor. The sensor design comprises the absorbing layer deposited on clean glass substrate with comb-shape aluminum electrodes (interdigitated structure). The change in electrical impedance of the sensing film was monitored as the device was exposed to humidity. The variation of the plasma-polymerization parameters resulted in different humidity sensing properties which could be correlated to the results of Fourier transform infrared spectroscopy (FTIR). The deposited films exhibited a detectable response to RH ranging from 30 to 95% with low hysteresis, good reproducibility and stability in long-term use. Films with a greater thickness showed a significant decrease in the humidity sensing capability. FTIR analysis revealed the presence of SiH bonding groups, which are frequently linked to the film density. The increase in the plasma discharge power induced also a significant decrease in the diffusion process of water vapor inside the sensitive layer bulk.