Exploring New Metal Electrodes for Ferroelectric Aluminum-Doped Hafnium Oxide

In this paper, we explore new metal electrodes for ferroelectric capacitors based on Al-doped HfO2. We find that Ti/Pd, Ti/Au, and W top electrodes can induce much higher remanent polarization as compared to the traditional TiN top electrode. The endurance of the capacitors with Ti/Pd electrodes is also much better than that with TiN and W electrodes. These results indicate that Ti/Pd is a very promising candidate for ferroelectric Al-doped HfO2. In addition, we find that the remanent polarization reaches maximum when the annealing temperature is around 900 degrees C-950 degrees C. At a given annealing temperature, the optimal Hf-to-Al cycle ratio corresponding to the highest remanent polarization is around 23:1. With optimized process conditions, we demonstrate high-performance Ti/Pd gated ferroelectric Al-doped HfO2 capacitors with remanent polarization up to 20 mu C/cm(2), endurance higher than 10(8) cycles, and retention over ten years at room temperature. Another interesting feature of the ferroelectric capacitors with Ti/Pd electrodes is high tunability of polarization by external pulses, which will be important for neurosynaptic computing applications.