Acoustic Wave Filter Structure for Low-Distortion Multi-Band Reception
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Solution Overview
Problem
Existing acoustic wave filter devices, particularly in composite filter devices like multiplexers, suffer from signal distortion due to insufficient linearity, which affects reception sensitivity across multiple bands.
Innovation Solution
The proposed solution involves an acoustic wave filter device structure with a semiconductor substrate, a piezoelectric layer, and a low-acoustic-velocity film, where the piezoelectric layer is positioned between the substrate and the low-acoustic-velocity film, and an insulating film is included between the routing line and the piezoelectric layer to enhance linearity and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-acoustic-velocity film is disposed on a silicon substrate to confine elastic waves, then acoustic wave confinement is improved, but linearity deteriorates causing signal distortion
Solution Approach 1:
The patent introduces a semiconductor layer as an intermediary between the silicon substrate and the low-acoustic-velocity film. This intermediate semiconductor layer acts as a mediator that prevents direct contact between the routing lines and the piezoelectric layer, thereby eliminating the harmful capacitance effect while maintaining acoustic wave confinement through the low-acoustic-velocity film.
Solution Approach 2:
The patent segments the structure by dividing the direct interface between substrate and low-acoustic-velocity film into two separate layers: a silicon substrate layer and a semiconductor layer. This segmentation allows each layer to perform its specific function independently - the silicon substrate provides mechanical support and acoustic confinement, while the semiconductor layer provides electrical isolation to prevent signal distortion.
2Adaptability or versatility
If multiple acoustic wave filters are connected to share common antenna terminal, then multi-band support is improved, but intermodulation distortion increases affecting reception sensitivity
Solution Approach 1:
The semiconductor layer serves as an intermediary that electrically isolates the piezoelectric layers of different acoustic wave filters from each other while allowing acoustic wave confinement. This isolation prevents intermodulation distortion between multiple bands while maintaining the ability to support multiple frequency bands through the composite filter device.
3Device complexity
If routing line is directly connected to piezoelectric layer, then electrical connection is simplified, but linearity deteriorates due to capacitance effect
Solution Approach 1:
The semiconductor layer acts as an intermediary barrier between the routing line and the piezoelectric layer. This intermediate layer eliminates the direct capacitive coupling that causes linearity deterioration, while still allowing the routing line to electrically connect to the IDT electrode through the semiconductor layer without significant signal loss.
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 effectively improves linearity, reducing signal distortion and enhancing reception sensitivity across multiple bands, particularly in multiplexers handling signals like Band 7 Rx and 5 GHz WiFi bands.
Implementation Method 1
a low-acoustic-velocity film in which an acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer
Implementation Method 2
a piezoelectric layer, an IDT (interdigital transducer) electrode provided on the piezoelectric layer
Data Source
AI summary
An acoustic wave filter device includes a plurality of acoustic wave resonators. Each of the acoustic wave resonators includes a piezoelectric layer and an IDT electrode provided on the piezoelectric layer. On a surface opposite to a surface of the piezoelectric layer on which the IDT electrode is provided, a low-acoustic-velocity film and a substrate made of a semiconductor are stacked. A routing line electrically connected to an antenna terminal is provided on an insulating film provided on the piezoelectric layer.