Fujifilm Corp developed lead zirconate titanate (PZT) that realizes twice as high a piezoelectric constant as existing PZT by adding highly concentrated niobium (Nb) to PZT.PZT is used for detecting distortion and as a piezoelectric device that can be distorted by applying a voltage. It can be used for a wide variety of sensors and actuators such as pressure sensors, acceleration sensors, gyroscopes, printer heads, magnetic heads for hard disk drives, micro pumps and micro-mirrors.
Nb added with sputtering method
This time, Fujifilm used a sputtering method to form a piezoelectric thin film by adding Nb to PZT (the ratio of Nb is about 13%). Its piezoelectric constant is -d31=250pm/V, which is much higher than that of existing PZT (about -d31=130pm/V), it said.
It has been known that piezoelectric constant can be improved by adding Nb to PZT, but Fujifilm said, "With the existing production method that uses a sol-gel process, Nb separates out after its ratio exceeds about 3%."
However, Fujifilm employed an RF magnetron sputtering method and succeeded in forming a PZT thin film containing a high ratio of Nb on a silicon (Si) substrate. The substrate temperature is about 500°C, and the deposition rate is about 4?m/h. The thickness of the film can be adjusted within the range of 1-5µm.
No need for polarization process
With the new PZT, even soon after a PZT thin film is formed, the direction of its polarization is uniform. Normal PZT does not function as a piezoelectric substance soon after it is sintered. To use it as a piezoelectric substance, it is usually necessary to apply a high voltage to the sintered object so that the direction of its polarization becomes uniform (polarization process).
On the other hand, the new PZT does not require a polarization process. By checking its diffraction pattern in an X-ray diffraction analysis (XRD analysis), Fujifilm confirmed that it is strongly oriented toward (100).
