The piezoelectric response of the PZT thin film was investigated for two different crystalline orientations (PZT(110) and PZT(100)) by increasing the applied voltage from 0 V to +9 V,
then decreasing it to −9 V and raising it back to 0 V (i.e. E ranging from −140 to +140 kV/cm) in steps of 0.5 V.
At each step, 30 diffraction patterns with an exposure time of 20 s each were recorded.
Before increasing the voltage to the following step, the voltage was reduced to 0 V for 200 s in order to minimize a possible heating by the Joule effect as described before.
From the change of the 2θ position of the center of the respective Bragg peak at 0 V and at the applied potential, the strain induced by the piezoelectric effects was calculated
. Fig. 3(a) and (b) displays the 2θ profiles for the PZT 110 and 100 reflections, respectively,
recorded at U = 0 V and U = 9 V. Based on those findings, strain profiles for the PZT (110) and the PZT (100) were calculated
Fig. 3(c) displays the piezoelectric strain for the two PZT reflections as a function of the applied voltage,
revealing “butterfly loops” [32]
. These loops are a clear signature for a piezoelectric hysteresis in the thin film.
The piezoelectric effect is a factor of ~2 stronger for grains oriented with [100] out-of-plane direction than for grains oriented with [110] out-of-plane direction,
evidencing piezoelectric anisotropy.
Considering a linear voltage drop over the entire film thickness of 710 nm, the piezoelectric coefficient in the lab reference frame dperp at U = 9 V for the PZT (100)
and PZT (110) yields ~230 and ~110 pm/V,
respectively. These values are in good agreement with theoretical piezoelectric coefficients found in literature for these two crystalline orientations [33,34].