Evaluation of Si:HfO₂ Ferroelectric Properties in MFM and MFIS Structures

Abstract

A 10.5 nm silicon doped HfO2 film is deposited and examined on three different bottom electrodes: a TiN electrode such as would be found in capacitive FeRAM, a lightly doped p-Si substrate as would be present in an FeFET, and an n+ Si electrode. The HfO2 stack deposited on n+ silicon is shown to have a coercive voltage of 2.9 V compared to 1.9 V for the film deposited on TiN. This is shown to be due to a 1.2 nm oxide present at the HfO2/Si interface dropping 36% of the voltage that is applied to the ferroelectric film stack. An FeFET fabricated with the film shows a 0.55 V threshold voltage shift due to ferroelectric polarization charge for a maximum applied gate bias of 5 V. After accounting for non-zero flat-band voltages, a 5 V bias on the transistor gate is shown to correspond to a 5.3 (μC/cm2) remnant polarization in the ferroelectric film. This corresponds with a theoretical maximum threshold voltage shift of 9.46 V, indicating that there is significant room for growth in FeFET performance if materials and processing challenges can be overcome.

Keywords

• Ferroelectric devices
• ferroelectric films
• field effect transistors