Thin Film Piezoelectric Element with Multi-Phase Stack for Large Stroke
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Solution Overview
Problem
Conventional thin film piezoelectric elements have inadequate piezoelectric constants and coercive field strength, limiting their stroke and reliability in actuator and sensor applications, particularly in disk drive units, due to single-phase structures that are prone to depolarization at high field strengths.
Innovation Solution
A thin film piezoelectric element with a piezoelectric thin film stack comprising a top and bottom electrode layer sandwiching a piezoelectric layer with different phase structures, such as rhombohedra and tetragonal phases, or compositions at the morphotropic phase boundary, to enhance coercive field strength and thermal stability, allowing larger applied field strengths without depolarization and achieving a larger stroke.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-phase piezoelectric layer is used, then the manufacturing process is simple, but the piezoelectric constants are inadequate and the coercive field strength is limited
Solution Approach 1:
The patent employs a composite piezoelectric layer comprising multiple phases (tetragonal phase and rhombohedral phase) with different compositions. This composite structure combines the advantages of each phase to achieve both high piezoelectric constants and enhanced coercive field strength, resolving the contradiction between manufacturing simplicity and performance reliability
Solution Approach 2:
The patent creates local quality variations by forming different piezoelectric phases with specific compositions (e.g., Pb(Zr1-xTix)O3 with different x values) within the same layer. This allows different regions to contribute different properties, achieving high piezoelectric constants in some regions while maintaining high coercive field strength in others
2Length of moving object
If the applied field strength is increased beyond the coercive field strength, then the stroke can be larger, but depolarization occurs reducing reliability
Solution Approach 1:
The patent changes the material parameters by incorporating multiple piezoelectric phases with different coercive field strengths. This creates a distribution of coercive fields that allows the element to withstand higher applied field strengths without complete depolarization, enabling larger stroke while maintaining reliability
Solution Approach 2:
The multi-phase structure acts as a cushioning mechanism against depolarization. When the applied field exceeds the coercive field of one phase, the other phases with different coercive characteristics provide resistance, preventing sudden complete depolarization and allowing larger field excursions
3Strength
If the PZT thickness is increased to enable larger applied field strength, then the field strength can be increased, but the cost rises
Solution Approach 1:
Instead of increasing thickness, the patent changes the compositional parameters by incorporating multiple phases with different coercive characteristics. This allows achieving higher applied field strength capability through material composition optimization rather than geometric scaling, avoiding the cost increase associated with thicker materials
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 significantly increases piezoelectric constants d31 and d33, enables larger applied field strengths without depolarization, and provides good thermal stability, enabling larger strokes and improved performance in devices like micro-actuators and disk drive units.
Implementation Method 1
Piezoelectric material is processed into various piezoelectric elements in accordance with different purposes, particularly, it has been widely used for functional electronic components such as an actuator for generating deformation by applying voltage
Implementation Method 2
or a sensor for generating voltage from the deformation of elements in a reverse way
Data Source
AI summary
A thin film piezoelectric element of the present invention includes a substrate and a piezoelectric thin film stack formed on the substrate. The piezoelectric thin film stack includes a top electrode layer, a bottom electrode layer and a piezoelectric layer sandwiched between the top electrode layer and the bottom electrode layer, wherein the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer whose compositions have different phase structures. The present invention can obtain high piezoelectric constants, enhanced coercive field strength and good thermal stability, thereby enabling larger applied field strength without depolarization and achieving a large stroke for its applied device.