Suspended Quartz MEMS RF Filter Integration to Cut Substrate Loss
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Solution Overview
Problem
Existing methods for integrating inductors and capacitors on silicon substrates for RF filters result in mechanical energy loss and RF losses due to the substrate, complicating miniaturization and increasing costs, while adding quartz resonators as hybrids leads to stray capacitance and increased complexity.
Innovation Solution
The integration of RF passive components directly on a quartz film using MEMS technology, where the quartz film is suspended over a substrate, minimizing RF losses and parasitics by isolating mechanical modes and reducing parasitic capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If inductors and capacitors are integrated on silicon substrate using conventional lithography, then device integration is achieved, but mechanical energy loss and RF losses occur due to substrate coupling
Solution Approach 1:
The device is segmented into distinct functional layers: a first substrate for mechanical resonators, a second substrate for passive components (inductors and capacitors), and a suspended quartz film connecting them. This segmentation isolates mechanical energy confinement to the resonators while separating RF signal paths from mechanical modes, eliminating substrate coupling losses.
Solution Approach 2:
A suspended quartz film acts as an intermediary between the mechanical resonators on the first substrate and the passive components on the second substrate. This quartz intermediary provides mechanical support and electrical connectivity while maintaining isolation between mechanical and RF domains, preventing energy loss through substrate coupling.
2Reliability
If quartz resonators are added as hybrids with wire bond attachments, then high Q applications are enabled, but stray capacitance increases affecting filter performance
Solution Approach 1:
The invention merges the quartz resonator substrate with the passive component substrate through direct integration on the suspended quartz film. Inductors, capacitors, and resonators are co-integrated without wire bonds, eliminating stray capacitance from external attachments while maintaining high Q performance through the low-loss quartz medium.
Solution Approach 2:
The harmful wire bond attachments are extracted from the design. Instead of adding quartz resonators as hybrids with wire bonds, the invention integrates all components directly on the suspended quartz film, removing the source of stray capacitance while preserving the high Q characteristics of quartz resonators.
3Loss of energy
If Si substrate is removed to reduce RF losses, then RF losses are reduced, but process complexity increases and packaging density decreases
Solution Approach 1:
Instead of removing the entire silicon substrate, the invention applies local quality changes by suspending only the specific region containing the mechanical resonators and passive components over a gap. The substrates remain in place for structural support and packaging, while the suspended portion provides RF loss reduction through isolation from lossy substrate materials.
Solution Approach 2:
The design transitions from a planar 2D integration to a 3D suspended structure. By creating a gap beneath the quartz film and suspending it from the substrates, the invention adds a vertical dimension that isolates the RF signal path from the substrate, reducing RF losses without complicating the fabrication process or reducing packaging density.
4Device complexity
If passive components are placed on silicon wafers, then integration is achieved, but RF losses in the substrate reduce circuit Q
Solution Approach 1:
The device is segmented into distinct functional layers: a first substrate for mechanical resonators, a suspended quartz film for signal transmission, and a second substrate for passive components (inductors and capacitors). This segmentation isolates RF signal paths from lossy substrate materials, maintaining high circuit Q while achieving full integration of resonators and passive components.
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 enables the production of filters with higher Q, lower insertion loss, and wider bandwidth in compact designs, simplifying fabrication and reducing manufacturing costs while maintaining high performance across VHF and UHF frequencies.
Implementation Method 1
a piezoelectric resonator element that includes a first electrode plate on the first side of the insulating substrate, and a second electrode plate on the second side of the insulating substrate
Implementation Method 2
the insulating substrate being separated from the base substrate by a gap, thereby isolating mechanical modes
Implementation Method 3
an inductive element having a coil
Implementation Method 4
a capacitive element having two conductive plates
Data Source
AI summary
An integrated Micro-Electro-Mechanical Systems (MEMS) filter includes an insulating substrate bonded to a base substrate such that at least a portion of the insulating substrate is separated from the base substrate by a gap, the insulating substrate having a first side and a second side, an inductive element having a coil, wherein the coil of the inductive element is on the insulating substrate, and a capacitive element having two conductive plates, wherein one of the two conductive plates is on the insulating substrate.