Fatigue free ferroelectric Pb₅Ge₃O₁₁ thin films prepared by metalorganic chemical vapor deposition

Fatigue free ferroelectric Pb5Ge3O11 (PGO) films have been prepared using metalorganic chemical vapor deposition (MOCVD). [Pb(thd)2] and [Ge(OC2H5)4] were used as the precursors for lead and germanium, respectively. The PGO films were deposited onto Ir/Ti/SiO2/Si and Pt/Ti/SiO2/Si wafers to measure their compositions, phase formation, microstructures and ferroelectric properties. The X-ray pattern showed the formation of C-axis oriented PGO films. All the PGO films showed excellent fatigue characteristics: no fatigue was observed up to 1 × 109 switching cycles. It is believed that the superior fatigue properties of these PGO films are due to the PGO lattice structure. PGO materials have large polarization along the c axis, but little or no polarization along a and b axis, thus the domain configuration is 180°. This is one reason that PGO has excellent fatigue properties, which is similar to Bi-layered oxides such as SrBi2Ta2O9 material. A typical 300-nm thick PGO film exhibited a saturated and square hysteresis loop. The remanent polarization (2Pr) and coercive field (2Ec) values at 5V were about 3.72 μC/cm2 and 67 kV/cm, respectively. The leakage current increased with increasing applied voltage, and is about 9.5 × 10−7 A/cm2 at 100 kV/cm. The maximum dielectric constant is about 35. The MOCVD PGO films can be used for single transistor memory applications.