Technique for the measurement of d₃₁ coefficient of piezoelectric thin films

This paper describes a new technique by which the d₃₁ coefficient of piezoelectric thin films can be characterized. Silicon substrates coated with lead-zirconate titanate (PZT) are flexed while clamped in a uniform load rig. When stressed, the PZT film produces an electric charge which is monitored together with the change in applied load. The mechanical stress and thus the transverse piezoelectric coefficient can then be calculated. Experiments were conducted as a function of poling field strength and poling time. Results are dependent upon the value of applied stress, which itself is dependent upon the mechanical properties of the silicon substrate. Because the substrate is anisotropic, limiting d₃₁ values were calculated. In general, d₃₁ was found to be approximately 20 pC/N for field strengths above 130 kV/cm and poling times of less than 1 minute. d₃₁ was increased more than a factor of three, to approximately 77 pC/N, when poled at 200 kV/cm for approximately 21 hours.