Metastable Ferroelectric Oxide Compositions for Thin-Film Phase Stability
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Solution Overview
Problem
Existing ferroelectric materials like HfO2 face challenges with high energy phases and multiple competing phases, limiting their stability and applicability in thin films for devices such as capacitors, sensors, and transistors.
Innovation Solution
Identify meta-stable ferroelectric oxides with low energy phases (Pca21, Pmn21) by using isovalent and aliovalent combinations of specific metal oxides, and provide a strategy to synthesize these phases on appropriate substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HfO2 is used as a ferroelectric material in thin films, then it retains its ferroelectric property even at 1 nm thickness, but it has high energy phase (Pca21) that is not the lowest energy phase and has multiple competing phases
Solution Approach 1:
The patent changes the chemical composition parameters by introducing dopants (Si, Al, Y) and forming solid solutions with ZrO2 to modify the energy landscape of HfO2 phases. This stabilizes the desired Pca21 ferroelectric phase by lowering its energy relative to competing phases, making it the ground state or near-ground state phase in thin film configurations.
Solution Approach 2:
The patent creates composite oxide systems by combining HfO2 with ZrO2 (forming HfxZr1-xO2 solid solutions) and incorporating dopant elements. These composite materials exhibit stabilized ferroelectric phases that are more stable than pure HfO2, resolving the phase stability issue while maintaining the thin film ferroelectric property.
2Reliability
If the FE phase of HfO2 is stabilized by using appropriate substrate or doping, then the ferroelectric property is maintained, but the device complexity and manufacturing process become more complicated
Solution Approach 1:
The patent modifies the compositional parameters of HfO2 by systematic doping with various elements (Si, Al, Y, Ta, Nb, Sc) and forming solid solutions with ZrO2. This changes the thermodynamic stability of different phases, enabling the ferroelectric Pca21 phase to be stabilized through composition control rather than requiring complex substrate engineering or multiple doping steps.
Data Source
AI summary
A meta-stable ferroelectric structure including one of the following oxides: an isovalent combination of the formula MxM′1-xO2-δ, wherein M, M′={Zr, Hf, Pb, W, Mo, Nb, Te, Ti}, 0≤x≤1, 0≤δ≤0.5 excluding {HfxZr1-xO2 all x in Pca21 phase}; an aliovalent combination of the formula MIxMII1-xO2-δ, wherein MI, MII={Bi, Y, Ta, In, Mo, Nb, Sc, Tl, Pd, Sb, W, Cr, Ge, Rh, Ti, Ag, Sn, Au, Ir, Pd, Ni, Ru, Hg}, 0≤x≤1, 0≤δ≤0.5, excluding certain aliovalent combinations; or an isovalent-aliovalent combination of the formula MxMIyMII1-x-yO2-δ, wherein M, MI, and MII are as set forth above, 0≤x≤1, 0≤y≤1, 0≤δ≤0.5; wherein the ferroelectric structure is in a Pca21 or Pmn21 space group or a subgroup thereof.