Piezoelectric Element Growth Control Layer
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Solution Overview
Problem
Existing piezoelectric elements, particularly PZT films, face challenges in maintaining high drive reliability in high-humidity environments due to the formation of pyrochlore phases and excess Pb, which degrades their dielectric and piezoelectric properties, and existing techniques fail to adequately control Pb composition and phase stability.
Innovation Solution
A piezoelectric element structure comprising a substrate, a lower electrode layer, a growth control layer with a specific metal oxide formula, and a perovskite-type oxide piezoelectric layer, where the growth control layer includes metal elements capable of substituting for the A site of the perovskite-type oxide, controlling the Pb composition and preventing pyrochlore phase formation through precise compositional ratios and electronegativity ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If PZT film is deposited with increased amount of Pb during initial layer deposition, then pyrochlore phase formation is inhibited, but drive reliability in high-humidity environment deteriorates due to excess Pb in interfacial region
Solution Approach 1:
The patent divides the PZT film deposition into multiple stages with different Pb compositions: an initial layer with increased Pb to prevent pyrochlore phase, followed by subsequent layers with controlled Pb content to ensure drive reliability. This segmentation allows each layer to serve its specific function without compromising the other.
Solution Approach 2:
The patent applies different Pb compositions to different regions of the film structure. The initial layer (interfacial region) contains increased Pb for phase stability, while the upper layers contain controlled Pb for reliability, creating local quality variations that address different functional requirements at different locations.
2Ease of manufacture
If normal vapor deposition is used without special measures, then manufacturing process is simple, but pyrochlore phase forms and degrades piezoelectric properties
Solution Approach 1:
The patent applies a preliminary action by depositing an initial layer with increased Pb content before the main PZT layer. This preliminary layer prevents pyrochlore phase formation in the subsequent layers, ensuring phase stability without requiring complex continuous control throughout the entire deposition process.
3Reliability
If Pb composition is strictly controlled to minimize excess Pb, then drive reliability is improved, but pyrochlore phase forms during deposition
Solution Approach 1:
The patent segments the deposition process into an initial layer with excess Pb for phase stability and subsequent layers with controlled Pb for reliability. This segmentation resolves the contradiction by allowing excess Pb only where it serves the phase stability function, while maintaining controlled Pb content in the functional layers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves high drive reliability in high-humidity environments by inhibiting pyrochlore phase formation and maintaining a stable perovskite structure, ensuring effective piezoelectric performance without excessive Pb, thereby enhancing the long-term reliability of PZT films.
Implementation Method 1
the growth control layer includes metal elements capable of substituting for the A site of the perovskite-type oxide, controlling the Pb composition and preventing pyrochlore phase formation through precise compositional ratios and electronegativity ranges
Implementation Method 2
Lead zirconate titanate (Pb(Zr,Ti)O3, hereinafter referred to as PZT) thin films, which have superior piezoelectricity and ferroelectricity
Implementation Method 3
Because of their ferroelectricity, PZT films are used for ferroelectric random access memory (FeRAM)
Data Source
AI summary
A piezoelectric element includes, in sequence, a substrate, a lower electrode layer, a growth control layer, a piezoelectric layer including a perovskite-type oxide containing lead as a main component of an A site, and an upper electrode layer. The growth control layer includes a metal oxide represented by MdN1−dOe, where M is one or more metal elements capable of substituting for the A site of the perovskite-type oxide. When the electronegativity of M is X, 1.41X−1.05≤d≤A1·exp(−X/t1)+y0, where A1=1.68×1012, t1=0.0306, and y0=0.59958. The perovskite-type oxide is represented by (Pba1αa2)(Zrb1Tib2βb3)Oc, where 0.5<a1/(b1+b2+b3)<1.07.