Ferroelectric Pb5Ge3O11 MFMOS capacitor for one transistor memory applications

Abstract

The basic mechanism for an one transistor memory device has been studied. Many ferroelectric materials such PbZr_xTi_1−xO₃ (PZT), SrBi₂Ta₂O₉ (SBT), Pb₅Ge₃O₁₁ (PGO) etc. were analyzed for this application. Because of its low remanent polarization and low dielectric constant, the c-oriented Pb₅Ge₃O₁₁ thin film was selected for one-transistor memory applications. Pb₅Ge₃O₁₁ thin films have been prepared using MOCVD and RTP (Rapid Thermal Process) post-annealing. Lead bis-tetramethylheptadione [Pb(thd)₂] and germanium ethoxide [Ge(OC₂H₅)₄] were used as the precursors. The Pb₅Ge₃O₁₁thin films were deposited onto Ir/Ti/SiO₂/Si wafers to measure their compositions, phase formation, microstructure and ferroelectric properties. The extremely highly c-oriented Pb₅Ge₃O₁₁ thin films showed good ferroelectric and electrical properties. A 300 nm thick PGO thin film exhibited a square and saturated hysteresis loop with 2Pr of 3.98 μC/cm², 2Ec of 128 KV/cm at an applied voltage 5V, leakage current of 5.1×10⁻⁷ A/cm² at 100 KV/cm, and dielectric constant of close to 36. The c-axis oriented Pb₅Ge₃O₁₁ thin film also exhibited very good retention properties. The experimental results showed that a Pb₅Ge₃O₁₁ MFMOS gate stack is suitable for one-transistor memory applications.