Cavity-Type FBAR Structure Without Sacrificial Layer Etching
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Solution Overview
Problem
Existing methods for constructing cavity-type film bulk acoustic wave resonators require a sacrificial layer, which can damage the film, reduce quality, and leave corrosive residues, affecting device performance.
Innovation Solution
A method that forms a cavity on the piezoelectric single crystal wafer before bonding, without using a sacrificial layer, by ion-implanting the wafer, growing a bottom electrode, and then bonding it to a substrate with an organic polymer bonding compound, followed by heat treatment to peel off the film and form a top electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a sacrificial layer is used to form the cavity, then the cavity structure can be obtained, but the film quality deteriorates and corrosive residues are formed
Solution Approach 1:
The invention extracts and removes the sacrificial layer concept entirely from the process. Instead of using a sacrificial layer that needs to be etched away, the cavity is formed directly in the substrate before bonding, eliminating the source of corrosive residues and film damage while maintaining the desired cavity structure.
Solution Approach 2:
The cavity is formed in the substrate before the piezoelectric film is bonded to it. This preliminary action of creating the cavity structure in advance avoids the need for subsequent etching processes that would expose the film to corrosive chemicals, thereby preserving film quality.
2Manufacturing precision
If etching is performed from the film surface to remove sacrificial layer, then the cavity can be formed, but the film is damaged and quality reduces
Solution Approach 1:
Instead of etching from the film surface downward to remove a sacrificial layer, the invention inverts the process by forming the cavity in the substrate upward or laterally before bonding. This reverses the sequence of operations so that the film is never exposed to etching chemicals, preserving its integrity and quality.
3Ease of manufacture
If the piezoelectric film is deposited on the electrode layer, then the device structure is formed, but the film quality deteriorates due to lattice mismatch
Solution Approach 1:
The invention introduces an intermediate substrate layer between the electrode and the piezoelectric film. This intermediary layer serves as a buffer that accommodates lattice mismatch, allowing the piezoelectric film to be deposited with high quality while maintaining the desired device structure.
4Manufacturing precision
If the wafer bonding transfer method is used, then high-quality piezoelectric films can be obtained, but the process complexity increases
Solution Approach 1:
The invention merges the cavity formation step with the substrate preparation step, performing both operations in sequence before bonding. This consolidation of steps into a streamlined process maintains high film quality through proper substrate preparation while reducing overall process complexity compared to separate sacrificial layer and etching procedures.
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 improves the mechanical strength of the device, reduces the complexity of the process, and enhances the quality of the film, resulting in a higher Q value and reduced clutter in the resonator, while eliminating the need for a sacrificial layer.
Implementation Method 1
It converts electrical energy into sound waves through the inverse piezoelectric effect of the piezoelectric film to form resonance
Implementation Method 2
using an ion-implanted piezoelectric single crystal wafer
Implementation Method 3
performing heat treatment on the bonded intermediate formed in step 1 to peel off the film from the piezoelectric single crystal wafer
Data Source
AI summary
Provided in the present invention are a cavity-type bulk acoustic resonator without the need to prepare a sacrificial layer, and a preparation method therefor, comprising the following steps: taking a piezoelectric single crystal wafer subjected to ion implantation and having a bottom electrode, and forming a cavity on the side of the piezoelectric single crystal wafer having the bottom electrode; then taking a substrate, and bonding the substrate to the side of the piezoelectric single crystal wafer having the cavity; performing heat treatment on the bonded intermediate product to peel off the thin film of the piezoelectric single crystal wafer; and producing a top electrode on the peeled side of the piezoelectric single crystal wafer. The preparation method for the cavity-type bulk acoustic resonator without the need to prepare a sacrificial layer set forth in the present invention does not require the growth of a sacrificial layer, and does not perform etching and hole-forming on the thin film; the mechanical strength of the device is increased, and the thin film is not easily damaged; the cavity structure is formed before film forming, yield is high, and residue from etching is not left after film forming, there being no need to consider the effect of incomplete release on the device.