82 Sensors and Acrccators B, 18-19 (1994) 82-84 A new surface acoustic wave humidity sensor based on a polyethynylfluorenol membrane C. Caliendo and E. Verona Istitutodi Awstica ‘O.M. Co&w’, CNR, via Cassia 1216, I-00189 Rome (Italy) A. D’Amico IstihUodi Elettronica, Universitli di Roma ‘Tor Verpata’, via Fontanile di Carcaricola, I-00156 Rome (Ita&) A. Furlani, G. Iucci and M.V. Russo* Dipartimentodi Chimica, Universitd di Roma zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ‘L.A Sapienza’, P.le A. Mom 5, I-00185 Rome (Italy) Abstract A device for surface acoustic wave (SAW) measurements, based on a polymeric sensitive membrane, that is polyethynylfluorenol (PEFI), has been realized. The SAW/PEFI sensor shows relatively fast and highly sensitive responses in the range of relative humidity O-60%. The enhanced sensitivity of the SAW/PEFl device, in comparison with that of a SAW sensor which utilized a polyphenylacetylene film, may be attributed to the presence of OH groups belonging to the polymer repeat unit. 1. Introduction Studies concerning chemical and physical applications of devices using surface acoustic waves (SAW) have received a great deal of interest [l-6]. In particular chemical sensors based on the SAW detection technique are interesting because the mechanism of interaction with the membrane material involves the peculiar prop- erties of the material itself, leading to a variety of surface acoustic modes over a wide range of frequencies zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJI [71. Previous studies, performed in our group, showed that iodine doped polyphenylacetylene (PPA) films can be successfully used as sensitive membranes for the fabrication of gas sensors, which exhibit electrical re- sponse towards relative humidity (r.h.) variations in the range 2040% [8,9]. We found also that a novel polymer, polyethynyliluorenol (PEFl) doped with SnCl,, is a suitable material for the development of a sensor which revealed current intensity variations while exposing the sensitive surface to relative humidity variations of the environment or to different concentrations of some chemical substances in the vapour phase [lo]. Moreover undoped PPA was studied as the sensitive membrane of a SAW-based humidity sensor which was tested over a wide range of r.h. values, giving reversible and fast response results [ll]. *Author to whom correspondence should be addressed. In this paper the results concerning the response to r.h. of a SAW sensor which is based on a PEFI film (SAWLF’EFl) will be presented. PEFl is a r-conjugated organic polymer with bulky chain pending groups, that are expected to induce a peculiar chemical interaction with water molecules. The measurements performed on the SAW sensor with the PEFl membrane will be discussed in comparison with the data obtained from the humidity sensor which uses the already reported PPA film [ll]. 2. Experimental PEFl was synthesized by catalytic polymerization of the monomer in the presence of Rh(I), Pd(I1) and Pt(I1) complexes [12]. It is stable at normal ambient conditions and under X-ray radiation; it is soluble in the most common organic solvents and can be deposited as thin film by spinning. Characterization of PEFl performed with ‘H and 13C NMR, together with IR spectroscopy, shows that the hydrogens and the pending groups are in a random cir-trons sequence with respect to the chain C=C bonds. From the molecular weight measurements (made by the osmometric method) an average polymer length corresponding to that of _ 10-20 monomer units was found. The SAW/PEFl humidity sensor response was tested on a delay line implemented on an ST-cut,n-propagation 09254005/94/$7.00 0 1994 Elsevier Sequoia. All rights reserved SSDI 0925-4005(93)00922-L