強誘電体薄膜のメモリー応用

抄録

Ferroelectric random access memory (FRAM) is one of the most promising devices applications of thin film ferroelectric materials. To develop FRAMs with high reliability it is important to understand how the properties of ferroelectric capacitors are impacted by process integration which exposes the capacitor to hydrogen at high temperature. At first we evaluated the hydrogen degradation of Pb(Zr, Ti)O₃ (PZT) capacitors by baking in Deuterium (D₂) gas. D₂ gas baking caused the same type of degradation as observed with H₂. We showed that the hydrogen degradation mechanism occurs in three steps: 1) partial reduction of IrO₂ top electrode to Ir, 2) dissociation of D₂ to D by Ir catalytic action, 3) D diffusion into PZT film. Next, we showed the capability of MOCVD-PZT films for future FRAMs. A large switching charge with low applied voltage and high reliability are obtained with highly (111)-oriented PZT layers. The measured switching charge is sufficient for 0.18 mm FRAM technology.