MEMS Vibrator Electrode Layout for Higher Dielectric Strength
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Solution Overview
Problem
In MEMS devices, the connection between the upper electrode and relocation wiring leads to a decrease in dielectric strength due to material combinations, causing issues with voltage application and electrostatic discharge resistance.
Innovation Solution
The MEMS device employs an offset connection mode where the relocation wiring applies voltage to a metal layer that does not overlap with the region where voltage is applied to the piezoelectric thin film, using a protective film and parasitic capacitance reduction film to prevent diffusion and enhance dielectric strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper electrode is connected to relocation wiring by removing the protective film to expose the electrode, then electrical connection is achieved, but dielectric strength at the contact portion is lowered
Solution Approach 1:
A barrier metal layer is introduced as an intermediary between the relocation wiring and the upper electrode. This barrier layer prevents direct contact between the wiring material and piezoelectric body, maintaining dielectric strength while allowing electrical connection through the protective film region.
Solution Approach 2:
The connection structure is moved from a vertical cross-sectional contact (through the protective film) to a planar offset arrangement. The relocation wiring contacts the upper electrode at a position offset in the plane direction from the piezoelectric body contact region, eliminating material diffusion while maintaining electrical connectivity.
2Ease of operation
If the relocation wiring directly contacts the upper electrode through via holes in the protective film, then voltage application is enabled, but material diffusion occurs under thermal loads
Solution Approach 1:
The barrier metal layer serves as a mediator that allows electrical connection while preventing thermal diffusion. It is positioned between the relocation wiring and the piezoelectric body contact region, blocking material diffusion pathways while maintaining voltage application capability.
Solution Approach 2:
The barrier metal layer is formed in advance before the relocation wiring is deposited. This preliminary action creates a diffusion barrier that prevents material contamination during subsequent thermal processing steps, ensuring composition stability from the outset.
3Reliability
If the protective film is removed to create contact between upper electrode and relocation wiring, then electrical connectivity is established, but electrostatic discharge resistance decreases
Solution Approach 1:
The contact geometry is changed from a cross-sectional via hole contact to a planar offset contact. The relocation wiring contacts the upper electrode at an offset position in the plane, maintaining electrical connectivity while preserving the protective film barrier that resists electrostatic discharge.
Solution Approach 2:
The barrier metal layer acts as an intermediary that enables electrical connection while maintaining the protective film's integrity. It allows current flow through the offset contact region without creating weak points that would reduce electrostatic discharge resistance.
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 configuration improves dielectric strength and electrostatic discharge resistance by preventing diffusion of contact materials into the piezoelectric thin film, even under thermal loads, without affecting the resonator's Q value or temperature characteristics.
Implementation Method 1
sandwiching a piezoelectric body between upper and lower electrodes and applying a voltage to the electrodes
Data Source
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AI summary
Provided is a MEMS device that includes a piezoelectric film, a first electrode and a second electrode sandwiching the piezoelectric film, a protective film provided to cover at least part of the second electrode and having a cavity that opens part of the second electrode, a third electrode that makes contact with the second electrode at least in the cavity and is provided so as to cover at least part of the protective film, and a first wiring layer having a first contact portion in contact with the third electrode.