Ferroelectrics Based on HfO2 Film

The discovery of ferroelectricity in HfO2 thin film, which is compatible with the CMOS process, has revived interest in ferroelectric memory devices. HfO2 has been found to exhibit high ferroelectricity at a few nanometers thickness, and studies have rapidly progressed in the past decade. Ferroelectricity can be induced in HfO2 by various deposition methods and heat treatment processes. By combining ferroelectric materials with field-effect transistors, devices that combine logic and memory functions can be implemented. Ferroelectric HfO2-based devices show high potential, but there are some challenges to overcome in endurance and characterization. In this paper, we discuss the fabrication and characteristics of ferroelectric HfO2 film and various applications, including negative capacitance (NC)), Ferroelectric random-access memory (FeRAM), Ferroelectric tunnel junction (FTJ), and Ferroelectric Field-effect Transistor (FeFET).

Effects of Oxygen Precursor on Resistive Switching Properties of CMOS Compatible HfO2-Based RRAM

In this work, we investigate the resistive switching behaviors of HfO2-based resistive random-access memory (RRAM) in two different oxidants (H2O and O3) in an atomic layer deposition system. Firstly, the surface characteristics of the Ni/HfO2/Si stack are conducted by atomic force microscopy (AFM). A similar thickness is confirmed by scanning electron microscope (SEM) imaging. The surface roughness of the HfO2 film by O3 (O3 sample) is smoother than in the sample by H2O (H2O sample). Next, we conduct electrical characteristics by current–voltage (I–V) and capacitor–voltage (C–V) curves in an initial process. The forming voltage of the H2O sample is smaller than that of the O3 sample because the H2O sample incorporates a lot of H+ in the film. Additionally, the smaller capacitor value of the H2O sample is obtained due to the higher interface trap in H2O sample. Finally, we compare the resistive switching behaviors of both samples by DC sweep. The H2O sample has more increased endurance, with a smaller on/off ratio than the O3 sample. Both have good non-volatile properties, which is verified by the retention test.

Characterization of Al Incorporation into HfO2 Dielectric by Atomic Layer Deposition

This study presents the characteristics of HfAlO films for a series of Al incorporation ratios into a HfO2 dielectric by atomic layer deposition on a Si substrate. A small amount of Al doping into the HfO2 film can stabilize the tetragonal phase of the HfO2, which helps to achieve a higher dielectric constant (k) and lower leakage current density, as well as a higher breakdown voltage than HfO2 film on its own. Moreover, assimilation of Al2O3 into HfO2 can reduce the hysteresis width and frequency dispersion. These are indications of border trap reduction, which was also verified by the border trap extraction mechanism. X-ray photoelectron spectroscopy (XPS) analysis also verified the HfAlO microstructural properties for various Al compositions. In addition, higher amounts of Al2O3 in HfAlO resulted in better interface and dielectric behavior through trap minimization, although the equivalent-oxide-thickness (EOT) values show the opposite trend.