SAW Multiplexer Filters Using Dielectric Layers for Narrow Bandwidths
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Solution Overview
Problem
Existing filter chips for communication applications face challenges in achieving a compact design with small bandwidth filters due to the limitations in reducing the pole-zero distance of SAW-resonators without increasing area consumption.
Innovation Solution
The integration of first-type SAW-resonators with a thin, dielectric, non-piezoelectric intermediate layer between the electrode structure and the piezoelectric layer, which reduces the coupling factor and pole-zero distance, allowing for smaller bandwidth filters with reduced area consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pole-zero distance of SAW-resonators is reduced to achieve smaller bandwidth filters, then the bandwidth of filters is reduced, but the area consumption increases
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the interdigital electrode structure and the piezoelectric layer. This dielectric layer mediates the coupling between the electrodes and the piezoelectric material, reducing the coupling factor and pole-zero distance without requiring increased area. The dielectric layer acts as a mediator that modifies the electromagnetic field distribution and reduces the direct capacitive coupling, thereby achieving smaller bandwidth filters with controlled area consumption.
Solution Approach 2:
The coupling factor and pole-zero distance are adjusted by changing the parameters of the dielectric layer, specifically its permittivity and thickness. By selecting appropriate dielectric materials with different permittivity values and optimizing the layer thickness, the coupling factor can be precisely controlled to achieve the desired pole-zero distance and filter bandwidth without increasing the resonator area.
2Area of stationary object
If multiple filters are integrated into a single chip to reduce device size, then the device complexity increases, but the area consumption is reduced
Solution Approach 1:
The dielectric layer structure with adjustable permittivity and thickness serves multiple functions simultaneously: it reduces the coupling factor, controls the pole-zero distance, enables bandwidth filtering, and allows for compact integration of multiple filters. This multi-functional approach reduces device complexity by using a single structural element (the dielectric layer) to achieve multiple objectives that would otherwise require separate components.
Solution Approach 2:
By varying the parameters of the dielectric layer (permittivity, thickness) across different filter regions, multiple filters with different bandwidths and characteristics can be integrated on a single chip. This parameter-based differentiation allows for compact multi-filter integration without requiring complex separate structures for each filter, thereby managing device complexity while achieving area reduction.
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 enables the realization of small bandwidth filters with minimal area consumption, allowing multiple filters to be integrated into a single chip, which is essential for communication devices like mobile phones.
Implementation Method 1
SAW-resonators are electro-acoustic resonators comprising an interdigital electrode structure on top of a piezoelectric layer
Implementation Method 2
The filters are configured such that an RF-signal can be applied to the input terminal, is then filtered by the filter, and the filtered signal can be picked up at the output terminal
Data Source
AI summary
The SAW filter chip comprises a plurality of SAW filters (1, 2), wherein at least one of the several electric filters is a first-type electric filter (1) comprising at least one first-type SAW-resonator (10). The first-type SAW-resonator comprises a piezoelectric layer (11), an intermediate layer (12) on the piezoelectric layer (11) and an interdigital electrode structure (13) on the intermediate layer (12). The interdigital electrode structure is separated from the piezoelectric layer by the intermediate layer. The intermediate layer is made of a dielectric, non-piezoelectric material and adjusts the electromechanical coupling factor and the bandwidth of the respective filter. The plurality of SAW filters form an LTE multiplexer, wherein the thickness of the intermediate layer is chosen to adjust the required bandwidth to the desired bands. The intermediate layer may be absent for larger required bandwidths.