Method of manufacturing a layered structure for a MEMS apparatus and MEMS apparatus having such a layered structure
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Solution Overview
Problem
Existing MEMS apparatus manufacturing methods using Deep Reactive Ion Etching (DRIE) result in surface damage and unevenness on functional layer sidewalls, leading to high stress and premature fractures due to scallops, sidewall breakthroughs, and right-angled corners, which reduce mechanical breaking limits and susceptibility to breakage.
Innovation Solution
A method involving a high-temperature curing step, such as hydrogen annealing or sacrificial oxidation, is applied to smooth sidewalls and round corners of the functional layer, followed by encapsulating the piezoelectric layer under a high-temperature-stable dielectric or electrode layer to protect it during curing, thereby enhancing fracture stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If Deep Reactive Ion Etching (DRIE) is used to structure the functional layer, then deep trenches and movable bodies can be formed, but surface damage and unevenness occur on sidewalls leading to premature fractures
Solution Approach 1:
A protective coating is applied to the sidewalls of the functional layer before the DRIE etching process. This preliminary protective measure prevents direct exposure of the sidewalls to the etching plasma, thereby reducing surface damage and scallop formation while still allowing the etching to create the desired deep trenches and movable bodies with high structural precision.
Solution Approach 2:
A protective coating layer serves as an intermediary between the etching plasma and the functional layer sidewalls. This intermediate layer absorbs the harmful effects of the etching process on the sidewalls, preventing direct damage while allowing the etching to proceed effectively through the coating material to create the required structural features.
2Productivity
If high-rate etching is used to form deep trenches, then structuring efficiency is improved, but scallops and sidewall breakthroughs occur causing high stress
Solution Approach 1:
A protective coating is introduced as an intermediary layer that interfaces with the etching plasma. This coating allows the high-rate etching process to proceed at high speed while simultaneously preventing the plasma from directly damaging the functional layer sidewalls, thereby eliminating scallop formation and sidewall breakthroughs that would otherwise occur at such high etching rates.
Solution Approach 2:
The protective coating converts the potentially harmful high-energy plasma environment into a beneficial process by allowing aggressive etching to occur through the coating material while protecting the underlying functional layer sidewalls from damage, thus transforming a harmful effect into a useful high-speed etching capability.
3Manufacturing precision
If mask is used for structuring, then pattern definition is achieved, but direct transfer into functional layer material causes right-angled corners
Solution Approach 1:
The protective coating acts as an intermediary layer between the mask pattern and the functional layer. This intermediate coating layer allows the mask to define the pattern accurately while preventing direct transfer of the mask geometry into the functional layer, thereby eliminating the formation of right-angled corners and allowing for smoother corner geometries in the final structure.
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
The method significantly increases the fracture limits of movable elements and spring structures, allowing for larger deflection angles and amplitudes without premature fractures, with sidewall roughness reduced to less than 50 nm, enhancing the mechanical stability of MEMS apparatus.
Implementation Method 1
a piezoelectric layer (4), in particular preferably on a side of the functional layer (3) opposite the substrate layer (1)
Implementation Method 2
a high-temperature curing step, such as hydrogen annealing or sacrificial oxidation
Implementation Method 3
a high-temperature curing step, such as hydrogen annealing or sacrificial oxidation
Data Source
AI summary
The present disclosure relates to a method of manufacturing a layered structure for a MEMS apparatus, a layered structure manufactured by the method, and a MEMS apparatus 200 (300, 400, 500) comprising the layered structure. For the layered structure, a high-temperature curing step is provided in the manufacturing process, for example, after structuring the functional layer 3. The structured regions and trenches of the functional layer 3 and in particular the spring structure formed in the functional layer 3 have smoothened side walls and/or rounded corners in regions 3a after the curing step, so that their fracture limits can thus be increased and early fractures of the functional layer 3 during operation of the MEMS apparatus 200 (300, 400, 500) can be avoided.