BAW Resonator Fabrication With Substrate Removal and Grain Control
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Solution Overview
Problem
The manufacturing process of Bulk Acoustic Wave (BAW) resonators, particularly Film Bulk Acoustic Wave Resonators (FBARs), faces challenges due to significant changes in crystal grain orientation of the piezoelectric layer, leading to decreased electromechanical coupling factor and Q value, and electrical losses caused by the substrate.
Innovation Solution
A method involving the formation of a first stack with a flat substrate, where a piezoelectric layer is deposited without direct contact with the substrate's protrusions, and a second stack is joined to eliminate the substrate, using sacrificial and intermediate layers to maintain crystal grain orientation and acoustic impedance for improved resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the piezoelectric layer is deposited directly on the substrate with protrusions, then the manufacturing process is simpler, but the crystal grain orientation changes significantly leading to decreased electromechanical coupling factor and Q value
Solution Approach 1:
A planarization layer is introduced as an intermediary between the substrate and the piezoelectric layer. This planarization layer fills the protrusions and provides a flat surface for piezoelectric layer deposition, preventing crystal grain orientation changes while maintaining manufacturing feasibility through standard semiconductor processing techniques.
2Device complexity
If the substrate is retained in the structure, then the device structure is more compact, but electrical losses occur due to substrate interaction
Solution Approach 1:
The substrate is completely removed from the final device structure through sacrificial layer etching. This extraction eliminates the source of electrical losses while the device maintains structural integrity through the carefully designed stack of functional layers that replace the substrate's mechanical support function.
3Ease of manufacture
If the piezoelectric layer contacts substrate protrusions, then the deposition process is easier, but the electromechanical coupling factor decreases
Solution Approach 1:
The substrate surface is pre-planarized by filling protrusions with planarization layer material before piezoelectric layer deposition. This preliminary action creates a uniform surface that ensures consistent crystal grain orientation throughout the piezoelectric layer, maintaining high electromechanical coupling factor while keeping the deposition process straightforward.
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 method enhances the electromechanical coupling factor and Q value of the resonance device by preventing crystal grain orientation changes and eliminating substrate-induced electrical losses, while also reducing fabrication costs through recyclable materials.
Implementation Method 1
an acoustic wave is generated by the piezoelectric layer under the alternating voltages with different polarities
Implementation Method 2
the acoustic waves need to be totally reflected on an upper surface of an upper metal electrode and a lower surface of a lower metal electrode to form standing acoustic waves
Data Source
AI summary
A method for forming a bulk acoustic wave resonance device is provided, includes: forming a first stack, and said forming the first stack includes providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity preprocessing layer on the piezoelectric layer, and a cavity is to be formed based on the cavity preprocessing layer, the cavity preprocessing layer at least covers a first end of the first electrode layer, and the cavity preprocessing layer is in contact with the piezoelectric layer, a first side of the first stack corresponds to a side of the first substrate, and a second side of the first stack corresponds to a side of the cavity preprocessing layer; forming a second stack, and said forming the second stack includes providing a second substrate; joining the first stack and the second stack, and the second stack is disposed at the second side; removing the first substrate, and the first side corresponds to a side of the piezoelectric layer; forming a second electrode layer at the first side, and the second electrode layer is in contact with the piezoelectric layer; and removing the second stack.