Ferroelectric HfO2-based thin films are attractive candidates for nonvolatile memories technologies such as ferroelectric random access memory (FRAM) and ferroelectric field effect transistors (FeFETs). Conventional perovskite ferroelectric memories have been unable to scale to high densities and are not CMOS compatible, which has prevented ferroelectric-based memory technologies from being widely adopted despite their low read/write power, high read/write speeds, and impressive cycling properties. Ferroelectric HfO 2 thin films can overcome the integration hurdles associated with perovskite ferroelectrics because HfO2 can be deposited through conformal atomic layer deposition (ALD), exhibit ferroelectric properties down to 5nm thicknesses, and are CMOS compatible.
A variety of processing techniques and devices were investigated to study the ferroelectric behavior of HfO2 based thin films under different conditions. When dopants such as Si and Al were incorporated into HfO 2, mutually competing phase transitions produced paraelectric, ferroelectric, or antiferroelectric characteristics. The overall concentration of such dopants and the spatial distribution of the dopant layers was shown to substantially impact ferroelectricity in HfO2. The fully miscible HfxZr 1-xO2 composition was adjusted to produce a range of ferroelectric and antiferroelectric properties. Layered concentration gradients of Hf and Zr within HfxZr1-xO2 thin films were demonstrated to add further capabilities in the ability to engineer the electrical and ferroelectric properties of HfO2-based thin films.
Extrinsic effects such as the device structure, the substrate and capping electrode material, and defects, such as oxygen vacancies, were observed to influence the overall behavior of ferroelectric HfO2-based thin films. Due to the ultra-thin dimensions of HfO2-based ferroelectrics, interactions between the electrode and ferroelectric interface were found to induce space charge effects and depolarization fields. The overall reliability of HfO2-based ferroelectrics was heavily influenced by the choice of electrode material, anneal temperature, and applied electric field.
Hf0.5Zr0.5O2 thin films doped with Al or Si exhibited antiferroelectric characteristics in which reversible field-induced phase transitions took place. The large energy storage density and high efficiency of antiferroelectric thin films make them exceptional candidates for on-chip energy storage. Reliability tests at elevated temperature were carried out to demonstrate the cycling characteristics of doped Hf0.5Zr 0.5O2 antiferroelectrics and the data retention of HfO 2-based ferroelectrics.
|Commitee:||Gila, Brent, Guo, Jing, Nishida, Toshikozu, Yoon, Y. K.|
|School:||University of Florida|
|Department:||Electrical and Computer Engineering|
|School Location:||United States -- Florida|
|Source:||DAI-B 80/07/(E), Dissertation Abstracts International|
|Subjects:||Electrical engineering, Nanotechnology|
|Keywords:||Antiferroelectricity, FRAM, Ferroelectricity, HfO2, Memory, Thin films|
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