Piezoelectric Thin Film Filter Electrode Layout for Lower Insertion Loss
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Solution Overview
Problem
Piezoelectric thin film filters face increased resistance and insertion loss due to the deposition and etching of lower electrodes in series resonators, which affects the separation of resonant frequencies and overall filter performance.
Innovation Solution
The design includes a series lower electrode with a first electrode formed on the series cavity portion and a second electrode formed on the non-cavity portion, where the first electrode's thickness is less than or equal to two-thirds of the second electrode's thickness, and the electrode edge adjacent to the parallel electrode extends upward to match the parallel electrode's thickness, reducing surface resistance and improving frequency separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the lower electrode of the series resonator is etched to a predetermined thickness to separate resonant frequencies, then the resonant frequency separation is improved, but the resistance of the series resonator increases and insertion loss increases
Solution Approach 1:
The lower electrode of the series resonator is designed with non-uniform thickness: thinner at the center portion (above the series cavity) and thicker at the end portions. This local quality variation allows the center region to provide frequency separation while the thicker end regions maintain low resistance, resolving the contradiction between frequency separation and insertion loss.
Solution Approach 2:
The lower electrode is segmented into different thickness regions (center portion with first thickness, end portions with second thickness). This segmentation enables different functional zones within the same electrode structure, where the thinner center provides capacitive coupling for frequency separation and the thicker ends provide low-resistance electrical connection.
2Measurement precision
If the lower electrode thickness is reduced to improve frequency separation, then the resonant frequency separation is improved, but the resistance increases
Solution Approach 1:
The electrode thickness is locally optimized: the center portion has reduced thickness to enhance capacitive coupling and frequency separation, while the end portions maintain greater thickness to ensure low resistance. This local quality approach resolves the contradiction between frequency separation and resistance.
3Ease of manufacture
If a uniform thickness lower electrode is used, then the manufacturing process is simple, but the insertion loss increases due to resistance
Solution Approach 1:
The lower electrode employs local quality variation with different thicknesses in different regions, which can be implemented through standard semiconductor fabrication techniques such as selective etching or conformal deposition with planarization. This approach maintains manufacturing feasibility while significantly improving insertion loss performance.
Solution Approach 2:
The electrode is segmented into functional zones with different thicknesses, allowing each zone to be optimized for its specific function (frequency separation vs. low resistance) while using conventional fabrication processes to create the multi-thickness structure.
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 configuration reduces the series resonator's resistance by approximately 16.3 to 40.2%, leading to a 0.06 to 0.15 dB improvement in insertion loss, effectively enhancing the filter's performance by separating resonant frequencies and reducing insertion loss.
Implementation Method 1
a piezoelectric layer formed on the substrate, the parallel lower electrode, and the series lower electrode
Data Source
AI summary
A piezoelectric thin film filter includes: a substrate comprising a parallel cavity constituting the parallel resonator and a series cavity constituting the series resonator; a parallel lower electrode formed on a parallel substrate portion constituting the parallel resonator in the substrate; a series lower electrode formed on a series substrate portion constituting the series resonator in the substrate; a piezoelectric layer formed on the substrate, the parallel lower electrode, and the series lower electrode; and an upper electrode formed on the piezoelectric layer, wherein the series lower electrode comprises a first series lower electrode formed on a portion where the series cavity is formed in the series substrate portion, and a second series lower electrode formed on a portion where the series cavity is not formed in the series substrate portion, wherein a thickness of the first series lower electrode is less than or equal to a predetermined thickness.