Monolithic Duplexer Ground Planes for RF Isolation
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Solution Overview
Problem
Miniaturized and lightweight duplexers for mobile communication devices face challenges in achieving high isolation between transmitter and receiver filters due to increased sensitivity to inter-signal interference, as the frequency difference between signals is small.
Innovation Solution
A monolithic duplexer design featuring a device wafer with elements separated by ground planes and sealing parts, a cap wafer with protrusion parts and ground posts, and via holes for electrical connection, utilizing metal/metal bonding to prevent electromagnetic interference, allowing for high isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the duplexer is miniaturized to reduce size and weight, then the device dimensions are reduced, but the isolation between transmitter and receiver filters deteriorates due to increased sensitivity to inter-signal interference
Solution Approach 1:
The duplexer structure is divided into multiple segments including a device wafer, cap wafer, multiple ground planes (first ground planes between elements, second ground planes on cap wafer), ground posts, and sealing parts. This segmentation creates electromagnetic shields that isolate the transmitter and receiver filters, maintaining high isolation even in miniaturized form.
Solution Approach 2:
The patent implements a nested structure where the device wafer containing filters is enclosed within the cap wafer, with ground planes and ground posts forming concentric shielding layers. The first ground planes are positioned between elements on the device wafer, while second ground planes on the cap wafer face them, creating nested electromagnetic shields that prevent interference in the compact structure.
2Reliability
If ground planes are added to improve isolation between filters, then the isolation performance is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent combines multiple functions into integrated structures: ground planes are formed as continuous conductive layers that simultaneously serve as electromagnetic shields and structural support elements. The sealing parts integrate both sealing functionality and ground reference functions. This merging reduces the number of discrete components and simplifies manufacturing while maintaining isolation performance.
Solution Approach 2:
The ground planes serve multiple functions simultaneously: they provide electromagnetic shielding between filters, act as reference grounds for the RF circuits, provide structural support for mounting elements, and serve as heat dissipation paths. This multi-functionality reduces the need for separate components, simplifying the overall device structure.
3Reliability
If multiple ground planes and shielding structures are implemented to prevent electromagnetic interference, then the isolation is improved, but the manufacturing process complexity increases
Solution Approach 1:
Ground planes and ground posts are formed during the wafer fabrication process itself, before the final assembly. The first ground planes are deposited on the device wafer, and ground posts are formed on the cap wafer during their respective fabrication stages. This preliminary formation of shielding structures simplifies the final assembly process and ensures precise positioning.
Solution Approach 2:
The metal/metal bonding process between the device wafer and cap wafer automatically creates electrical connections between the first ground planes and second ground planes through the welding of sealing parts. This self-service mechanism establishes the ground references and shielding connections during the bonding process itself, eliminating the need for separate wiring or connection steps.
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
The design effectively prevents electromagnetic interference between integrated elements, enabling high isolation and supporting the miniaturization of RF devices while maintaining performance.
Implementation Method 1
The first sealing parts and the first ground planes on the device wafer are welded to the second sealing parts and the second ground planes, by a method of the metal/metal bonding, for example.
Data Source
Figure 1A~1C
Figure 1D~1F
AI summary
A monolithic duplexer and a fabrication method thereof. The monolithic duplexer includes a device wafer (10), a plurality of elements (1a,1b,1c,1d) distanced from each other on a top portion of a device wafer, first sealing parts (30) formed on the top portion of the device wafer, and a plurality of first ground planes (20) formed between the plurality of elements. A cap wafer (40) is also provided having an etched area for packaging the device wafer, a plurality of protrusion parts, a plurality of ground posts (42), and cavities. Second sealing parts (48) are formed on a bottom portion of the protrusion parts, and a plurality of second ground planes (46) cover the plurality of ground posts. Via holes (50) vertically penetrate the cap wafer to connect to the plurality of the second ground planes, and ground terminals (60) are formed on top portions of the via holes. The first sealing parts and the first ground planes are attached to the second sealing parts and the second ground planes, respectively.