BAW Resonator Stack With Opposite Polarization for Higher-Order Modes
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Solution Overview
Problem
Conventional BAW devices face challenges in achieving higher frequency operation without significantly thinning electrode and piezoelectric layers, leading to increased ohmic losses, decreased breakdown voltages, and reduced manufacturability as frequencies increase beyond 10 GHz.
Innovation Solution
The implementation of a BAW device with oppositely polarized piezoelectric layers, where the second piezoelectric layer has a crystal structure opposite to the first, enables higher-order resonance without thinning the layer stack by using a two-terminal configuration and optional intermediate layers to minimize thickness increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional BAW devices use thinner electrode and piezoelectric layers to achieve higher frequency operation, then operating frequency increases, but ohmic losses increase and breakdown voltages decrease
Solution Approach 1:
The piezoelectric layer is segmented into multiple distinct piezoelectric layers with different crystal orientations (e.g., first piezoelectric layer with <001> orientation and second piezoelectric layer with <111> orientation). This segmentation allows each layer to contribute differently to the acoustic wave generation, enabling higher frequency operation while maintaining sufficient layer thickness to reduce ohmic losses.
Solution Approach 2:
The device uses a composite structure combining multiple piezoelectric materials with different crystal orientations and properties. This composite approach allows optimization of each layer's contribution to frequency response while maintaining overall structural integrity and electrical performance, achieving high frequency operation without excessive thinning.
2Speed
If conventional BAW devices use thinner electrode and piezoelectric layers to achieve higher frequency operation, then operating frequency increases, but manufacturability becomes more challenging
Solution Approach 1:
Dividing the piezoelectric layer into multiple segments with different crystal orientations enables each layer to be optimized for specific manufacturing processes. This segmentation makes the fabrication process more manageable and less sensitive to variations in layer thickness, improving overall manufacturability while achieving high frequency operation.
Solution Approach 2:
The invention changes the crystal orientation parameter of different piezoelectric layers (e.g., <001> vs <111> orientations) to achieve different acoustic properties. This parameter variation allows optimization of both frequency response and manufacturability, as different orientations can be grown using established semiconductor fabrication techniques.
3Speed
If conventional BAW devices use thinner piezoelectric layers to achieve higher frequency operation, then resonant frequency increases, but power density increases
Solution Approach 1:
The composite piezoelectric structure with multiple layers of different crystal orientations distributes the power handling capability across layers. This allows the device to operate at higher resonant frequencies while maintaining lower power density through the distributed architecture, as each layer contributes differently to the overall acoustic wave generation.
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 design allows for higher frequency operation while maintaining layer thickness, reducing ohmic losses, and enhancing manufacturability, thus supporting frequencies beyond 10 GHz without the need for thinner layers.
Implementation Method 1
The input RF signal is provided to electrodes that are separated by a layer of piezoelectric material that expands and contracts in response to the input RF signal to create the acoustic waves
Implementation Method 2
Micro-acoustic filters convert an input RF signal into acoustic waves, filter the acoustic waves, and convert the filtered acoustic waves into an output RF signal
Implementation Method 3
The frequencies of acoustic waves that resonate in a layer stack of a BAW device are inversely related to the combined thicknesses of the electrodes and the piezoelectric layer
Data Source
AI summary
A bulk acoustic wave (BAW) device comprises a layer stack including first and second electrodes, a first piezoelectric layer between the electrodes, and a second piezoelectric layer between the first piezoelectric layer and the second electrode. A polarization of a crystal structure of the second piezoelectric layer is opposite to a polarization of a crystal structure of the first piezoelectric layer to achieve higher order resonant frequencies in the BAW device by means other than merely thinning layers in the layer stack. In some examples, the BAW device is a two-terminal device and does not include a metal layer configured to be a third electrode. In some examples, the BAW device includes at least one intermediate layer between the first and second piezoelectric layers, and a total combined thickness of the at least one intermediate layer is less than 4% of a total thickness of the layer stack.