Multiplexer, high-frequency front end circuit, and communication device
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Solution Overview
Problem
In multiplexers used in high-frequency front end circuits, higher-order modes of acoustic wave resonators can cause ripples in the pass band of other filters, leading to deterioration of filter characteristics, especially when a piezoelectric body made of lithium tantalate is laminated on a silicon substrate.
Innovation Solution
The design includes acoustic wave filters with specific configurations of support substrates, silicon nitride and oxide films, and IDT electrodes, where the wavelength normalized thicknesses and Euler angles of these components are optimized to prevent higher-order modes from occurring within the pass bands of other filters, using expressions to determine the frequencies of these modes and ensuring they fall outside the operational bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a piezoelectric body made of lithium tantalate is laminated on a silicon substrate, then heat resistance is improved, but higher-order modes appear causing ripples in pass bands of other filters
Solution Approach 1:
The patent changes the physical parameters of the acoustic wave resonator by controlling the thickness of the piezoelectric body and adjusting the electrode finger pitch to alter the acoustic wavelength. This parameter adjustment shifts the higher-order mode frequencies away from the pass bands of other filters, eliminating the ripple problem while maintaining the heat-resistant lithium tantalate substrate structure
Solution Approach 2:
The patent addresses the higher-order mode issue by transitioning from a two-dimensional surface acoustic wave to a three-dimensional bulk acoustic wave mode through careful design of the piezoelectric body thickness. This dimensional transition allows the acoustic wave to propagate in the thickness direction, fundamentally changing the mode structure and preventing harmful higher-order modes from appearing in other filter pass bands
2Device complexity
If multiple acoustic wave filters for different frequencies are commonly connected, then device integration is improved, but filter characteristics deteriorate due to higher-order mode interference
Solution Approach 1:
The patent applies parameter changes by adjusting the electrode finger pitch and piezoelectric body thickness to control the acoustic wavelength and higher-order mode frequencies. This allows multiple filters to be integrated with different frequency characteristics without mutual interference, as each filter's higher-order modes are positioned outside other filters' pass bands
Solution Approach 2:
The patent segments the frequency spectrum by designing each acoustic wave filter with specific pass bands that are isolated from the higher-order modes of other filters. This segmentation is achieved through precise control of resonator parameters, allowing multiple filters to coexist in a integrated device without characteristic deterioration
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 effectively prevents ripples caused by higher-order modes from appearing in the pass bands of other acoustic wave filters, thereby maintaining excellent filter characteristics and reducing the risk of filter deterioration.
Implementation Method 1
a piezoelectric body 15 made of lithium tantalate and an IDT electrode 16 provided on the piezoelectric body
Implementation Method 2
an acoustic wave resonator 11 includes a support substrate 12, a silicon nitride film 13 laminated on the support substrate 12, a silicon oxide film 14, and a piezoelectric body 15 laminated on the silicon oxide film 14
Data Source
AI summary
A multiplexer includes N acoustic wave filters each including one end connected in common and having a different pass band, in which when the N acoustic wave filters are in order from a side of a lower frequency of the pass band, at least one n-th acoustic wave filter among the N acoustic wave filters excluding an acoustic wave filter having the highest frequency of the pass band includes one or more acoustic wave resonators including a support substrate, a silicon nitride film laminated on the support substrate, a silicon oxide film laminated on the silicon nitride film, a piezoelectric body laminated on the silicon oxide film, and an IDT electrode provided on the piezoelectric body. All acoustic wave filters having a pass band in a higher frequency than a frequency of a pass band of the n-th acoustic wave filter satisfy fh1_t(n)>fu(m) or fh1_t(n)<fl(m).