Packaged Crystal Resonators on IC Substrates
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Solution Overview
Problem
Conventional wafer-scale fabrication techniques face challenges in achieving high-quality inductors for quartz, MEMs, and LC-based timing applications due to difficulties in forming inductors with low series resistance and smooth metal surfaces on integrated circuit substrates, particularly when adjacent to lossy materials, which reduces their quality factor (Q).
Innovation Solution
A method of forming crystal oscillator circuits involves depositing electrically conductive mounting cement to create electrode adhesion bumps and extensions on a crystal resonator, which are then cured to securely and electrically connect the resonator to the substrate, while also incorporating a patterned inductor within a hermetically sealed cavity to enhance inductor performance by minimizing loss and maintaining high Q factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional wafer-scale fabrication techniques are used to form inductors on integrated circuit substrates, then manufacturing scalability is improved, but inductor quality factor (Q) deteriorates due to high series resistance and lossy substrate materials
Solution Approach 1:
The inductor structure is segmented into multiple metal layers (first inductor metal layer and second inductor metal layer) stacked vertically, allowing the inductor to be formed in three dimensions rather than relying solely on planar expansion. This segmentation enables high-Q inductors to be integrated on standard CMOS substrates while maintaining manufacturing scalability
Solution Approach 2:
The inductor design transitions from two-dimensional planar spirals to three-dimensional stacked structures by adding vertical metal layers connected through via holes. This dimensional change increases the effective inductor area without expanding the substrate footprint, thereby improving Q factor while maintaining wafer-scale fabrication compatibility
2Device complexity
If inductors are formed adjacent to lossy materials on the substrate, then integration density is improved, but inductor quality factor (Q) deteriorates due to increased energy loss
Solution Approach 1:
The patent applies different material properties to different regions: the inductor metals are selected with high conductivity for the winding paths, while the substrate and surrounding structures use standard CMOS materials. The via holes are filled with conductive material to minimize resistance at critical connection points, creating locally optimized quality throughout the structure
Solution Approach 2:
The inductor structure combines multiple materials with complementary properties: copper or aluminum for the metal layers, dielectric materials for insulation, and conductive fill materials for via holes. This composite approach allows the inductor to achieve high Q factor while being integrated with lossy substrate materials
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 secures and electrically connects crystal oscillators to the substrate, improving the mechanical and electrical stability of the resonator and inductor, thereby enhancing frequency stability and reducing losses, resulting in high-quality inductors with improved Q factors.
Implementation Method 1
depositing electrically conductive mounting cement onto first and second electrically conductive mounting pads to thereby define first and second electrode adhesion bumps thereon
Implementation Method 2
electrically conductive mounting cement... to securely and electrically connect the resonator to the substrate
Implementation Method 3
crystal-based resonators... piezoelectric resonator element
Implementation Method 4
hermetically sealed cavity... to enhance inductor performance by minimizing loss
Implementation Method 5
inductors to support resonance frequencies and/or timing circuit operation... incorporating a patterned inductor... to enhance inductor performance
Data Source
AI summary
An integrated circuit device includes an integrated circuit substrate having a two piece package thereon. The package has a hermetically sealed cavity therein and a crystal resonator within the cavity. The crystal resonator includes at least one electrode electrically coupled to a portion of the integrated circuit substrate by an electrically conductive via, which extends at least partially through the package. The package may include a material selected from a group consisting of glass and ceramics. The crystal resonator includes a crystal blank and first and second electrodes on first and second opposing sides of the crystal blank. The package includes a base having a recess therein and a cap hermetically sealed to the base. The cap includes first and second electrical traces thereon, which are electrically connected to the first and second electrodes of the crystal resonator.