BAW Resonator Bragg Mirror Uniformity for High Q Factor
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Solution Overview
Problem
Conventional BAW Bragg mirror resonators have a low quality factor around the antiresonance frequency, are not temperature stable, and are challenging to produce due to parasitic coupling and thickness inaccuracies in silicon oxide layers, leading to frequency shifts and varying temperature behavior.
Innovation Solution
A method involving the deposition of a conductive layer and a uniform silicon oxide layer, followed by ion beam etching to ensure thickness uniformity better than 2% and the use of high conductivity materials like aluminum to minimize parasitic capacitances and enhance acoustic reflection, while maintaining standard manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional deposition processes are used for silicon oxide layers, then manufacturing is simpler, but thickness uniformity deteriorates (variations better than 2% are difficult to achieve)
Solution Approach 1:
The patent applies preliminary action by performing ion beam etching to remove excess silicon oxide before final deposition. This preliminary removal step ensures that subsequent deposition layers start from a uniformly etched surface, guaranteeing thickness uniformity better than 2% across the wafer while maintaining compatibility with standard manufacturing processes
2Reliability
If standard Bragg mirror structures are used, then manufacturing is easier, but quality factor around antiresonance frequency deteriorates (low quality factor)
Solution Approach 1:
The patent applies local quality by modifying the Bragg mirror structure locally in the regions between contact pads and substrate. Specifically, silicon oxide layers are removed in these inter-pad regions to eliminate parasitic capacitances, while preserving the standard alternating high/low impedance layer structure in the resonator regions. This localized modification improves quality factor without requiring complete redesign of the manufacturing process
3Manufacturing precision
If silicon oxide layer thickness varies, then deposition is simpler, but frequency performance deteriorates (frequency shifts and varying temperature behavior)
Solution Approach 1:
The patent applies feedback by using ion beam etching with real-time thickness monitoring to control the removal of silicon oxide layers. The ion beam process is adjusted based on measured thickness variations, ensuring that the final silicon oxide layer thickness is uniform across the entire wafer. This feedback-controlled approach guarantees frequency consistency and stable temperature behavior while remaining compatible with standard manufacturing workflows
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
Significantly improves the quality factor of BAW resonators, stabilizes temperature behavior, and ensures consistent frequency performance across resonators from the same wafer, reducing parasitic coupling and capacitance-related issues.
Implementation Method 1
reducing, by etching by means of an ion beam scanning the wafer, the thickness inequalities of the upper silicon oxide layer
Implementation Method 2
An insulating structure 7, for example a Bragg mirror, interfaces between the piezoelectric resonator 5 and the substrate 3... sends the waves back to the resonator
Implementation Method 3
When an electric field is applied to the piezoelectric layer by applying a potential difference between the electrodes, a mechanical disturbance results in the form of acoustic waves
Data Source
AI summary
The invention relates to a method for manufacturing a wafer on which BAW resonators (31) are formed, each resonator comprising: above a substrate (3), a piezoelectric resonator (5), and next to the piezoelectric resonator, a contact pad connected to an electrode of the piezoelectric resonator; and between the piezoelectric resonator and the substrate, a Bragg mirror (37), comprising at least one conductive layer (37b) extending between said at least one pad and the substrate (3), and at least one silicon oxide layer (37a) extending between the pad and the substrate, this method comprising the following steps: depositing the silicon oxide layer (37a); and reducing the inequalities in thickness of this layer (37a) related to the deposition process, so that it has the same thickness to better than 2%, and preferably to better than 1%, at the level of each pad.