Elaboration and modeling of water molecule sensitive layers deposited from hexamethyldisiloxane

Abstract

This paper reports the simulation study of humidity-sensitive and electrical properties of plasma polymerized hexamethyldisiloxane (pp-HMDSO) thin film based sensors. The humidity sensitive film was deposited by glow discharge at low frequency power (19 kHz) in a capacitively coupled parallel plate plasma reactor. The sensor design comprises the interdigitated electrodes and the absorbing layer. The sensor was calibrated in terms of impedance as a function of relative humidity (10–95 %), using a frequency response analyzer. The used frequency signal was fixed at 1 kHz with a signal amplitude of 3 V. The hexamethyldisiloxane thin film is investigated as humidity sensor. The elaborated sensor exhibited a small hysteresis (2 % RH) and fast response (8 and 34 s when the adsorption and desorption occur between 35 % of RH and 95 % of RH, respectively). The simulations results showed an increase in time characteristic of diffusion with the increase of sensitive layers thickness, which confirms the reduction in the sensitivity for thicker films. The performance of the films and the results of the model simulations are presented and discussed. The HMDSO film showed promising characteristics for humidity sensor development.