Target properties optimization on capacitive-type humidity sensor: Ingredients hybrid and integrated passive devices fabrication

Optimized hygroscopic film preparation and high-precision manufacturing guarantee the humidity sensor expected properties on sensitivity, hysteresis, response/recovery speed, reliability, etc. This paper demonstrated a comprehensive prioritization scheme on the premise of industrial production. Raw materials mixtures such as pyromellitic dianhydride (PMDA)/p-phenylenediamine (p-PDA), and PMDA/oxydianiline (ODA) were investigated to solve the issue of film surface collapse. Polyacrylonitrile (PAN) is adopted as an additive to enhance the film reliability (maximum of 0.15 % measurement error rate in 120 h continuous testing) as well as assistance in the film coating process. Rutile TiO₂ with the average particle size of 0.33 μm was employed as doping elements to reduce the hysteresis to 0.95 % relative humidity (RH), increase the sensitivity to 0.94 pF/% RH, and limit the response/recovery time within 40 s. The film-growth quality and the consistency of production performance were assured by the integrated-passive-device (IPD) fabrication process.