Inverted Ground Plane RF MEMS Package Design
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Solution Overview
Problem
Existing RF MEMS packages require modification to integrate a ground plane, which is challenging for substrates like quartz and silicon due to difficulties in creating vias, and limits the flexibility in material selection and signal density.
Innovation Solution
A RF MEMS package design with an inverted or flipped ground plane, where a secondary substrate with a ground plane is coupled to the MEMS device, forming a RF transmission line without the need for through-vias, allowing RF signal propagation without altering the MEMS device or its substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an integrated ground plane is integrated onto the bottom surface of the mounting substrate, then RF signal transmission is enabled, but the manufacturing complexity increases due to the need for via formation in quartz and silicon substrates
Solution Approach 1:
The ground plane is inverted from the conventional bottom-surface location to the top surface of the mounting substrate, positioned adjacent to the signal line. This inversion eliminates the need for through-substrate vias in quartz and silicon, as the ground plane is now accessible on the same surface as the signal line, allowing direct lateral connection without vertical penetration through the substrate thickness.
2Reliability
If vias are formed through the substrate to connect ground plane to ground lines, then electrical connection is achieved, but the manufacturing time and complexity increase
Solution Approach 1:
The complex via formation process is extracted and eliminated from the manufacturing sequence. Instead of forming through-substrate vias to connect the ground plane to ground lines, the ground plane is repositioned on the top surface where it can be laterally connected to ground lines through simple conductive traces, removing the time-consuming via formation step entirely.
3Loss of energy
If the electromagnetic field resides in the cavity between ground plane and MEMS device, then signal losses are reduced, but the device structure becomes more complex
Solution Approach 1:
The RF transmission line structure transitions from a planar two-dimensional configuration to a three-dimensional cavity structure. The ground plane is positioned adjacent to the signal line on the top surface, creating a controlled electromagnetic field cavity between the ground plane, signal line, and MEMS device. This dimensional change confines the electromagnetic field to a specific volume, reducing signal losses through better field control and reduced radiation, while the added structural complexity is offset by the performance benefits.
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 reduces signal losses and enables higher density signal lines, as the electromagnetic field primarily resides in a cavity between the ground plane and the MEMS device, and allows for the use of a wider range of materials without the need for complex via formation.
Implementation Method 1
Conductive signal line 14 and ground plane 18 interact with each other to create an electromagnetic wave that travels through dielectric substrate 12 to create a RF signal
Implementation Method 2
the interaction between the ground plane and the signal line create a RF transmission line wherein the top surface of the first mounting substrate is free of ground lines
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A radio frequency (RF) microelectromechanical system (MEMS) package includes a first mounting substrate, a signal line formed on a top surface of the first mounting substrate, the signal line comprising a MEMS device selectively electrically coupling a first portion of the signal line to a second portion of the signal line, and a ground assembly coupled to the first mounting substrate. The ground assembly includes a second mounting substrate, a ground plane formed on a bottom surface of the second mounting substrate, and at least one electrical interconnect extending through a thickness of the second mounting substrate to contact the ground plane, wherein the ground plane is spaced apart from the signal line.