Transverse piezoelectric coefficient measurement of flexible lead zirconate titanate thin films

摘要

Highly flexible lead zirconate titanate, Pb(Zr,Ti)O_3 (PZT), thin films have been realized by modified sol-gel process. The transverse piezoelectric coefficient d_(31) was determined from the tip displacement of bending-mode actuators made of PZT cantilever deposited onto bare or RuO_2 coated aluminium substrate (16 μm thick). The influence of the thickness of ruthenium dioxide RuO_2 and PZT layers was investigated for Pb(Zr_(0.57)Ti_(0.43))O_3. The modification of Zr/Ti ratio from 40/60 to 60/40 was done for 3 μm thick PZT thin films onto aluminium (Al) and Al/RuO_2 substrates. A laser vibrometer was used to measure the beam displacement under controlled electric field. The experimental results were fitted in order to find the piezoelectric coefficient. Very large tip deflections of about 1 mm under low voltage (～8 V) were measured for every cantilevers at the resonance frequency (～180 Hz). For a given Zr/Ti ratio of 58/42, it was found that the addition of a 40 nm thick RuO_2 interfacial layer between the aluminium substrate and the PZT layer induces a remarkable increase of the d_(31) coefficient by a factor of 2.7, thus corresponding to a maximal d_(31) value of 33 pC/N. These results make the recently developed PZT/Al thin films very attractive for both low frequency bending mode actuating applications and vibrating energy harvesting.