PMUT Fabrication via Single Metallization Shield and Contact
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Solution Overview
Problem
Existing methods for fabricating piezoelectric micromachined ultrasonic transducers (PMUTs) are complex and inefficient, particularly in forming electromagnetic shields and electrical contacts, which increases fabrication costs and cycle duration.
Innovation Solution
A method that integrates forming an electromagnetic shield, sealing a cavity, and creating electrical contacts in a single metallization process, using an intermediate layer with a sacrificial material and interposing material, reducing the need for multiple masks and improving alignment features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wafer bonding is used to fabricate PMUT, then the PMUT can be fabricated on a CMOS wafer, but bonding yield and complex interconnect design factors are introduced
Solution Approach 1:
The patent combines the electromagnetic shield, cavity seal, and electrical contact formation into a single metallization process. The metallic layer serves multiple functions simultaneously: it forms the electromagnetic shield over the piezoelectric stack, seals the cavity by filling and sealing the via, and creates electrical contacts through the intermediate layer to the wafer. This integration eliminates the need for separate bonding and interconnect formation steps, thereby improving both manufacturing ease and bonding yield.
2Adaptability or versatility
If PMUT is fabricated monolithically on a CMOS wafer, then integration is achieved, but the fabrication process becomes longer as MEMS device and CMOS wafer have to be serially fabricated
Solution Approach 1:
The patent uses an intermediate layer with pre-formed sacrificial material and interposing material that enables subsequent cavity formation and electrical contact creation in advance. The sacrificial material is positioned beforehand to define the cavity location, and the interposing material is pre-deposited to facilitate via formation. This preliminary preparation allows the electromagnetic shield, cavity seal, and electrical contacts to be formed in a single metallization step, significantly reducing the fabrication cycle duration while maintaining monolithic integration.
3Reliability
If existing technologies are used to form electromagnetic shield in monolithic PMUT, then the shield is created, but complex process flows are required
Solution Approach 1:
The metallic layer in the patent performs multiple functions simultaneously: it forms the electromagnetic shield over the piezoelectric stack, seals the cavity by filling and encapsulating the via, and creates electrical contacts through the intermediate layer to the wafer electrodes. This multi-functionality eliminates the need for separate process steps for shield formation, cavity sealing, and interconnect creation, thereby simplifying the process flow while ensuring reliable electromagnetic shielding.
4Manufacturing precision
If multiple masks are used in fabrication process, then precise patterning is achieved, but fabrication costs and process complexity increase
Solution Approach 1:
The patent combines the patterning of the electromagnetic shield, cavity seal, and electrical contacts into a single metallization process using a unified mask design. The metallic layer is patterned in one step to simultaneously define the shield regions, via fill regions, and contact regions. This integration reduces the number of masks required compared to conventional approaches that use separate masks for each feature, thereby reducing fabrication costs and process complexity while maintaining precise patterning through careful mask design.
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 simplifies the fabrication process, reduces costs by about 50%, and shortens the fabrication cycle duration compared to existing technologies.
Implementation Method 1
an active layer including a piezoelectric stack
Data Source
AI summary
According to various embodiments, a PMUT device may include a wafer, an active layer including a piezoelectric stack, an intermediate layer having a cavity therein where the intermediate layer is disposed between the wafer and the active layer such that the cavity is adjoining the piezoelectric stack. A via may be formed through the active layer and the intermediate layer to the wafer. A metallic layer may be disposed over the active layer and over surfaces of the via. The intermediate layer may include an interposing material surrounding the cavity, and may further include a sacrificial material surrounding the via. The sacrificial material may be different from the interposing material. The metallic layer may include a first member at least substantially overlapping the piezoelectric stack, a second member extending from the first member to the cavity, and a third member extending into the active layer to contact an electrode therein.