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Local crystallographic phase detection and texture mapping in ferroelectric Zr doped HfO2 films by transmission-EBSD

: Lederer, M.; Kämpfe, T.; Olivo, R.; Lehninger, D.; Mart, C.; Kirbach, S.; Ali, T.; Polakowski, P.; Roy, L.; Seidel, K.


Applied Physics Letters 115 (2019), Nr.22, Art. 222902, 6 S.
ISSN: 0003-6951 (Print)
ISSN: 1077-3118
Fraunhofer IPMS ()

The local crystal phase and orientation of ferroelectric grains inside TiN/Hf0.5Zr0.5O2/TiN have been studied by the analysis of the local electron beam scattering Kikuchi patterns, recorded in transmission. Evidence was found that the ferroelectric phase of the layers is derived from an orthorhombic phase, most likely of space group Pca21. The orientation analysis reveals a strong out-of-plane texture of the polycrystalline film which is in accordance with a high remanent polarization Pr observed for P-V measurements. The results of this analysis help us to further optimize the ratio of ferroelectric grains and their orientation for many applications, e.g., in the field of emerging memory or infrared sensors.
Highly textured ferroelectric films are required for high density nonvolatile memories such as ferroelectric field-effect transistors (FeFET), ferroelectric random-access memories (FeRAM), and ferroelectric tunneling junctions (FTJs). Since the discovery of ferroelectricity in ultrathin layers of Si doped HfO2, ferroelectric properties have been demonstrated in polycrystalline HfO2 films doped with various elements such as Y, Sr, Al, Si, or Zr. Even undoped HfO2 has been reported to exhibit ferroelectric properties, which proves that ferroelectricity is an intrinsic property of the confined material.
HfO2 is fully compatible with conventional complementary metal-oxide semiconductor (CMOS) processes and can be manufactured using many approaches, including atomic layer deposition (ALD). Therefore, it may prove superior to traditional perovskite structure based ferroelectric materials with regard to the applicability in ferroelectric devices. So far, highly scaled FeFETs with thin ferroelectric HfO2 layers have been fabricated at 28 nm and 22 nm
technology node high-k metal gate (HKMG) CMOS processes. Furthermore, the observed piezoelectric and pyroelectric properties reveal potential for future nanoelectromechanical systems (NEMS) and sensor applications.
It has been reported that the ferroelectricity of HfO2 originates from the orthorhombic phase with the space group Pca21 [Fig. 1(a)]. As this is a metastable phase, a multitude of different crystallographic phases and associated textures can be present in the films, which is influenced by external conditions such as stress, doping, thermal treatment, and film thickness.