SAW Filter Wafer Packaging With Low-Temperature Cavity Bonding
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Solution Overview
Problem
Traditional SAW filter wafer-level packaging methods face challenges such as large chip size, high production costs, and substrate cracking due to thermal expansion coefficient mismatches between silicon wafers and lithium tantalate or lithium niobate substrates, especially when using double-layer organic dry films and high-temperature silicon wafer bonding processes.
Innovation Solution
A surface acoustic wave filter wafer-level packaging structure that employs a dielectric layer to form cavity sidewalls and utilizes low-temperature Si—Si bonding, avoiding the need for heating and thus preventing substrate cracking, with a bonding layer and a second silicon substrate to enclose the cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-temperature silicon wafer bonding process is used, then bonding strength is improved, but substrate cracking occurs due to thermal expansion coefficient mismatch
Solution Approach 1:
The patent changes the bonding temperature parameter from high-temperature (conventional) to low-temperature process, which eliminates thermal expansion coefficient mismatch issues between silicon wafer and lithium tantalate/nickel substrates, preventing substrate cracking while maintaining bonding strength
Solution Approach 2:
The patent introduces an organic dry film as an intermediary bonding layer between the silicon wafer and the piezoelectric substrate. This intermediate layer accommodates thermal expansion differences and enables low-temperature bonding, serving as a mediator that prevents direct thermal stress transmission to the substrates
2Reliability
If double-layer organic dry film is used for cavity formation, then cavity sealing is improved, but chip size increases and production cost rises
Solution Approach 1:
The patent extracts and removes the double-layer organic dry film structure from the packaging design, replacing it with a simplified single-layer approach or alternative cavity formation method that maintains sealing effectiveness while reducing chip area and production complexity
Solution Approach 2:
The patent employs a single-layer organic dry film or alternative material that serves the cavity sealing function temporarily during bonding, then is removed or integrated, eliminating the need for complex double-layer structures and reducing overall chip size
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 fabrication of SAW filters with reduced chip size and lower production costs while avoiding substrate cracking, by using a dielectric layer and low-temperature bonding to align thermal expansion coefficients.
Implementation Method 1
utilizes low-temperature Si—Si bonding, avoiding the need for heating and thus preventing substrate cracking
Implementation Method 2
employs a dielectric layer to form cavity sidewalls and utilizes low-temperature Si—Si bonding
Data Source
AI summary
A surface acoustic wave (SAW) filter includes a filter wafer including: a first substrate; and an interdigital transducer (IDT) disposed on the first substrate, the IDT including a first input and output end, a second input and output end, and an interdigital portion. The SAW filter also includes a dielectric layer disposed on the filter wafer, covering the first input and output end and the second input and output end of the IDT and exposing the interdigital portion; a passivation layer disposed on the dielectric layer; a bonding layer disposed on the passivation layer; a second substrate bonded to the filter wafer via the bonding layer; and a cavity enclosed by the second substrate and the bonding layer.