Bulg. J. Phys. vol.40 no.3 (2013), pp. 224-228

Vacuum Deposited Polyimide Layers as Humidity Sensors

V. Strijkova, B. Georgieva
"Acad. J. Malinowski" Institute of Optical Materials and Technology, Bulgarian Academy of Sciences, "Acad. G. Bonchev" Str., bl. 109, 1113 Sofia, Bulgaria
Abstract. The polyimide layers are prepared by thermal vacuum co-evaporation of the precursors pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) and subsequent thermal treatment up to 250 or 300°$C. In this paper it is investigated the humidity sensing properties of polyimide layers (with thickness of 50 and 630 nm) by measuring the electrical resistance R [Ω] and the capacitance C [pF] as a function of the relative humidity RH [%]. The layers show very good characteristics as humidity sensors operating at room temperature -- the electrical resistance changes by more than 4 decades and the capacitance -- by 40% in the range of 20–100% RH.

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