Electro-ultrasonic spectroscopy of polymer-based thick film layers

We have studied the properties of polymer-based thick film layers by electro-ultrasonic spectroscopy. Electro-ultrasonic spectroscopy method is based on the interaction between ultrasonic vibrations and electrical conductivity of solids. The ultrasonic vibrations of frequency fU change the contact area between conducting grains in the thick film structure and then the resistance is modulated by the frequency of ultrasonic excitation. An intermodulation voltage is created on this structure. It depends on the value of AC current varying with frequency fE and on the ultrasonic excited resistance change ΔR varying with frequency fU. We have measured the intermodulation voltage Um for a set of polymer-based thick film resistors made by different resistive pastes. It was found that for given sample the intermodulation component of frequency fm = fE − fU increases linearly with electric excitation for the constant ultrasonic excitation. We have normalized the intermodulation voltage Um by the electric current IE and this quantity is proportional to the ultrasonic excited resistance change ΔR. The relative resistance change ΔR/RX is of the order of 10−7-10−4. From the comparison of the results measured for the samples made by the same resistive pastes it follows, that relative resistance change ΔR/RX can be used as an indicator of sample quality.