Multi-Layer Electrode for Piezoelectric Resonators
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Solution Overview
Problem
Conventional bulk acoustic wave (BAW) resonators require extensive surface treatment and high-density metal electrodes, which increase process complexity and manufacturing cost while also leading to electrical loss due to high resistance, reducing resonator performance.
Innovation Solution
A multi-layer electrode structure is introduced, comprising a high conductivity metal layer and a seed layer, which allows for the growth of a highly textured piezoelectric layer with reduced electrical loss and simplified surface preparation, thereby enhancing resonator performance and reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high density metal (molybdenum or tungsten) is used to form the lower and upper electrodes to increase electromechanical coupling, then electromechanical coupling is improved, but electrical resistance increases causing electrical loss and reduced resonator performance
Solution Approach 1:
The single high-density metal electrode layer is segmented into a multi-layer structure consisting of a first electrode layer (high-density metal for electromechanical coupling), a second electrode layer (low-resistance metal for electrical conduction), and optionally a third electrode layer. This segmentation allows each layer to specialize in its primary function, resolving the contradiction between coupling strength and electrical loss.
Solution Approach 2:
The electrode structure uses composite material composition by combining high-density metal (molybdenum or tungsten) with low-resistance metal (aluminum or copper) in a multi-layer configuration. This composite approach leverages the advantages of both material types: the high-density metal provides strong electromechanical coupling while the low-resistance metal minimizes electrical loss.
2Manufacturing precision
If extensive underlying layer surface treatment (chemical mechanical polishing and reactive etch treatment) and carefully chosen seed layer are used to achieve highly textured piezoelectric layer, then piezoelectric layer texture is improved, but process complexity and manufacturing cost increase
Solution Approach 1:
The method performs preliminary action by forming the multi-layer electrode structure before piezoelectric layer deposition. The specific sequence of depositing high-density metal, followed by low-resistance metal, and optionally performing selective removal creates a pre-configured surface that inherently promotes desired piezoelectric layer texture without requiring extensive subsequent surface treatment.
Solution Approach 2:
The invention changes the parameters of the underlying electrode structure by introducing multi-layer composition and controlled thickness ratios (e.g., first electrode layer thickness between 50-500 nm, second electrode layer thickness between 50-200 nm). These parameter changes create optimal surface conditions for piezoelectric layer nucleation and growth, reducing the need for additional surface treatment steps.
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 multi-layer electrode structure achieves a highly textured piezoelectric layer with reduced electrical loss and lower manufacturing complexity, resulting in improved BAW resonator performance and cost-effectiveness compared to conventional designs.
Implementation Method 1
When an electric field is applied across the piezoelectric layer via the upper and lower electrodes, electrical energy is converted into acoustic energy in the piezoelectric layer through electromechanical coupling
Implementation Method 2
a high conductivity metal, such as aluminum or copper, is situated over the acoustic mirror and under the seed layer
Data Source
AI summary
According to an exemplary embodiment, a method of forming a multi-layer electrode for growing a piezoelectric layer thereon includes a step of forming a high conductivity metal layer over a substrate. The method further includes a step of forming a seed layer over the high conductivity metal layer. The method further includes a step of forming a high density metal layer over the seed layer. The method further includes a step of forming a piezoelectric layer over the high density metal layer. The high conductivity metal layer, the seed layer, and the high density metal layer form the multi-layer electrode on which the piezoelectric layer is grown.