Platinum Metals Rev., 2000, 44, (3), 107
Palladium Oxide Layers as Damage Markers in RAMs
Materials being investigated to replace the traditional dielectrics used for memory storage, in DRAM (direct random access memory) and NVDRAM (nonvolatile DRAM), capacitors, include high permittivity (high-epsilon (HE)) and ferroelectric (FE) perovskites, such as (Ba,Sr)TiO3 and SrBi2Ta2O9. The materials for the electrodes used in these capacitors must be able to withstand the high-temperature oxidising conditions needed to deposit the perovskites, so noble metals and/or their conductive oxides have been tested, and platinum, in particular, has improved device properties. However, the reducing environments needed to process the devices can damage the perovskite, by loss of oxygen, resulting in high device leakage.
Scientists at IBM in New York, U.S.A. have now found a way of monitoring the damage to the perovskites (K. L. Saenger, C. Cabral, P. R. Duncombe, A. Grill and D. A. Neumayer, J. Mater. Res ., 2000, 15, (4), 961–966). They found an additional decomposable PdO sbottom electrode could act as a marker for observing any damage to the perovskite from the reducing environment. Oxygen loss from PdO layer films with and without a HE/FE overlayer was monitored by in situ XRD during heating in an inert ambient. The Pd could lose or gain oxygen or form a Pd-Pt alloy with an underlying Pt layer. Oxygen could cross the HE/FE in both directions. The Pt underlayer reduced the temperature at which oxygen left the PdO. The PdO layer could thus act both as a monitor and as an oxygen source for the perovskite.