Application of Silica Aerogel Films to the Fabrication of Surface Acoustic Wave Filters

Herein, silica aerogel films were used in the fabrication of surface acoustic wave(SAW) filters for the first time. Firstly, silica aerogel films with various silica sol driptimes were prepared and characterized. According to spectroscopic ellipsometry, therefractive index of an aerogel film with a silica sol drip time of 9 min decreased by5.9% compared with a film with sol drip time of 18 min in the intermediate region ofthe sample. The increase in sol drip time led to an increase in particle size andthickness, and a decrease in pore size. Secondly, four different types of SAW filterswere designed, i.e. covered with either air, poly(dimethylsiloxane) (PDMS), PDMSfilled with silica aerogel powder, or a silica aerogel film. Addition of silica aerogelpowder to PDMS increased the bandwidth of the resulting SAW filter to 2.362 MHz,increased its central frequency to 0.001 GHz and decreased its insertion loss to 1.545dB. Although they had low porosity, the SAW filters covered with silica aerogel filmshad a bandwidth of 60.586 MHz, a central frequency of 2.447 GHz, a Q value of 40.073, and the largest insertion loss of –15.397 dB. SAW filters with silica aerogel films withvarious sol drip times were also tested. The results indicated that more porous thesilica aerogel films, stronger is the signal strength and smaller is the insertion lossof the SAW filter. GRAPHICAL ABSTRACT