Piezoelectric Device Semi-Conducting Layer Charge Diffusion
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Solution Overview
Problem
Piezoelectric devices face issues with pyroelectric charge generation, leading to polarization inversion and electrode breakage due to high resistivity, which limits their application in devices like radio-frequency filters and multiplexers, as existing structures fail to effectively release pyroelectric charge without degrading electrical characteristics.
Innovation Solution
A piezoelectric device with a semi-conducting layer of specific resistivity and thickness is introduced between the piezoelectric thin film and the support substrate, allowing pyroelectric charge diffusion and preventing local electric field buildup, thus preventing polarization inversion and electrode breakage without requiring an undesirable electrode structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an insulating layer is disposed between the piezoelectric thin film and the support substrate, then bonding strength is improved, but pyroelectric charge is not released leading to polarization inversion and electrode breakage
Solution Approach 1:
The patent changes the electrical parameter of the bonding layer from insulating to semi-conducting, with a specific resistivity range of 1×10^-5 to 1×10^2 Ω·m. This parameter change allows the bonding layer to simultaneously provide mechanical bonding strength and electrical charge release functionality, resolving the contradiction between bonding strength and reliability.
Solution Approach 2:
The semi-conducting layer serves multiple functions: it acts as a bonding layer providing mechanical strength, while simultaneously functioning as a charge release path for pyroelectric charge. This multi-functionality eliminates the need for separate structures and resolves the contradiction between bonding and charge release requirements.
2Reliability
If an electrode structure for releasing pyroelectric charge is provided on the piezoelectric thin film, then pyroelectric charge is released, but radio-frequency signals leak through the electrode structure degrading device characteristics
Solution Approach 1:
The patent introduces a semi-conducting layer as an intermediary between the piezoelectric thin film and support substrate. This intermediary layer provides a controlled path for pyroelectric charge release while its semi-conducting properties prevent radio-frequency signal leakage, thus resolving the contradiction between charge release and signal integrity.
Solution Approach 2:
By changing the electrical resistivity parameter of the bonding layer to a semi-conducting range, the layer can selectively conduct pyroelectric charge (which occurs during thermal processing) while blocking radio-frequency signals (which occur during device operation), thereby resolving the contradiction between charge release and signal leakage.
3Reliability
If the piezoelectric body has high resistivity, then piezoelectric characteristics are maintained, but pyroelectric charge accumulates causing polarization inversion and electrode breakage
Solution Approach 1:
The semi-conducting layer acts as an intermediary charge sink that accepts pyroelectric charge from the high-resistivity piezoelectric body during thermal processing, preventing charge accumulation and polarization inversion, while not affecting the piezoelectric characteristics during normal operation.
Solution Approach 2:
The patent extracts the charge release function from the piezoelectric body itself and places it in the semi-conducting layer. This allows the piezoelectric body to maintain its high resistivity and piezoelectric characteristics while the semi-conducting layer handles the harmful pyroelectric charge accumulation during manufacturing and operation.
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 semi-conducting layer effectively diffuses pyroelectric charge, preventing polarization inversion and electrode breakage, while maintaining device characteristics, allowing for broader application of piezoelectric devices without the need for airtight packaging and reducing package costs.
Implementation Method 1
a large amount of pyroelectric charge is generated by application of heat
Implementation Method 2
the pyroelectric charge generated when heat is applied is diffused through the semi-conducting layer
Implementation Method 3
The semi-conducting layer is composed of a semiconductor material or a mixture of a metal and an oxide of the metal and has a volume resistivity of about 1×10^-5 (Ω·m) to about 1×10^2 (Ω·m)
Data Source
AI summary
A method for producing a piezoelectric device includes a laminate formation step in which a laminate including a piezoelectric thin film, a support substrate, a metal layer, and a silicon oxide film respectively stacked on both of an upper surface and a lower surface of the metal layer interposed between the piezoelectric thin film and the support substrate is formed, a semi-conducting layer formation step in which a semi-conducting layer is formed by oxidizing the metal layer, and a functional electrode formation step in which a functional electrode that is electro-mechanically coupled to the piezoelectric thin film is formed on a first principal surface of the piezoelectric thin film. The semi-conducting layer is a layer composed of a mixture of a metal constituting the metal layer and an oxide thereof, or a layer composed of a semiconductor which is an oxide of a metal constituting the metal layer.