FBAR Fabrication via Sacrificial Layer Etching
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Solution Overview
Problem
Existing methods for fabricating bulk wave acoustic resonators with suspended thin layers of piezoelectric material face difficulties in achieving precise thinning and decoupling from the substrate, particularly with techniques like ion implantation/fracture, which are complex and limited in thickness range.
Innovation Solution
A method involving the use of a sacrificial layer to form and then remove, allowing for the creation of a partially suspended thin layer of piezoelectric material between electrodes, enabling the fabrication of bulk wave devices like FBARs with improved planarization and assembly quality through steps like ion implantation, molecular bonding, and selective etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion implantation/fracture technique is used to thin the piezoelectric layer, then the layer thickness can be reduced to below 0.5 μm, but the method becomes complex and is limited in thickness range
Solution Approach 1:
A sacrificial layer is deposited on the piezoelectric layer before thinning operations. This preliminary action provides a protective and guiding structure that enables subsequent selective removal of the piezoelectric layer to form suspended regions, avoiding the complexity of direct thinning methods
Solution Approach 2:
The sacrificial layer acts as an intermediary element between the piezoelectric layer and the substrate. It facilitates the formation of suspended piezoelectric regions by being selectively removed after bonding, simplifying the overall fabrication process compared to direct ion implantation/fracture methods
2Ease of operation
If the piezoelectric layer is thinned to below a micron to create suspended structure, then FBAR type resonators can be achieved, but maintaining homogeneous thickness during thinning becomes very difficult
Solution Approach 1:
The sacrificial layer is deposited beforehand to define the regions where the piezoelectric layer will be selectively removed. This preliminary structuring enables controlled thinning while maintaining thickness homogeneity in the remaining suspended regions
Solution Approach 2:
The sacrificial layer is patterned to create local variations, allowing selective thinning of the piezoelectric layer in specific regions while maintaining the original thickness in other areas. This enables suspended structures with homogeneous thickness in the suspended regions
3Manufacturing precision
If implantation/fracture method is used to achieve very low thicknesses, then thickness below 0.5 μm can be obtained, but the method is limited to maximum thickness of 2 μm with conventional implanters
Solution Approach 1:
Instead of changing the piezoelectric layer thickness to achieve different device characteristics, the sacrificial layer thickness is varied. This allows the piezoelectric layer to maintain its optimal thickness range while the sacrificial layer adapts to provide the desired suspended structure geometry
Solution Approach 2:
The sacrificial layer serves as a mediator that decouples the piezoelectric layer thickness from the suspended region dimensions. This enables independent optimization of piezoelectric layer thickness for electrical performance while controlling suspended region geometry through sacrificial layer parameters
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
This approach simplifies the production of bulk wave resonators by enabling precise thin layer formation and decoupling, allowing for higher frequency filtering capabilities and improved device performance compared to existing technologies.
Implementation Method 1
the elimination of the sacrificial layer so as to unveil the said thin layer of piezoelectric material and the said first electrode
Implementation Method 2
the implantation of ions in the said first substrate so as to create in the piezoelectric material a buried weak zone defining the thin layer of piezoelectric material
Implementation Method 3
the assembling of the said first set with a second substrate
Data Source
AI summary
A method for fabricating a bulk wave acoustic resonator (FBAR) which includes at least locally a partially suspended thin layer of piezoelectric material, and includes the following steps: the formation of at least one first so-called lower electrode on the surface of a thin layer of piezoelectric material; the deposition of a so-called sacrificial layer on the surface of the said thin layer of piezoelectric material and of the said first electrode defining a first set; the assembling of the said first set with a second substrate; the formation of at least one second electrode termed the upper electrode on the opposite face of the said thin layer of piezoelectric material from the face comprising the said first electrode; and the elimination of the sacrificial layer so as to unveil the said thin layer of piezoelectric material and the said first electrode and define the bulk wave resonator.