Curved Piezoelectric Membrane Fabrication via Substrate Etching
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Solution Overview
Problem
Existing MEMS device fabrication methods fail to consistently produce membranes with curved features that are durable and efficient, leading to issues with power efficiency and longevity in piezoelectric actuators used in fluid ejection systems.
Innovation Solution
A process involving anisotropic etching and oxidation of semiconductor substrates to create profile-transferring surfaces with rounded intersections, allowing for the deposition of materials that form membranes with uniform, aligned grain structures and curved features, such as domes or dents, which are then used to fabricate durable and efficient piezoelectric actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fabrication methods are used to form piezoelectric membranes, then the manufacturing process is simple, but the membranes cannot achieve consistent curved features and uniform grain structures, resulting in poor durability and efficiency
Solution Approach 1:
The patent applies preliminary action by pre-forming curved features (domes or dents) in the substrate before depositing the piezoelectric material. This ensures that the grain structure of the deposited material naturally conforms to the curved profile, achieving uniform grain structures and consistent curved features without requiring complex post-processing or specialized deposition techniques.
Solution Approach 2:
The patent replaces mechanical forming methods with a deposition-based approach. Instead of mechanically shaping the piezoelectric membrane after deposition, the substrate profile is pre-formed and the material is deposited to conform to this profile, substituting mechanical post-forming with a deposition process that naturally follows the substrate geometry.
2Use of energy by moving object
If flat piezoelectric elements are used, then the fabrication process is straightforward, but larger displacement and power efficiency cannot be achieved
Solution Approach 1:
The patent applies curvature by forming domes or dents in the substrate before piezoelectric material deposition. This curvature enables the piezoelectric element to achieve larger displacement under the same driving voltage compared to flat elements, thereby improving power efficiency. The curved profile is maintained through conformal deposition that follows the substrate geometry.
Solution Approach 2:
The patent changes the geometric parameter of the piezoelectric element from flat to curved by pre-forming the substrate profile. This parameter change (from planar to curved geometry) directly increases the displacement capability of the element under applied voltage, improving the power efficiency of the fluid ejection system.
3Reliability
If rounded intersections are not formed in the recess, then the fabrication process is simpler, but the membranes lack durability under stress
Solution Approach 1:
The patent applies preliminary action by pre-forming rounded intersections in the substrate recess before piezoelectric material deposition. These rounded features eliminate stress concentration points that would otherwise compromise membrane durability. The rounding is achieved through controlled deposition and selective removal processes that prepare the substrate profile in advance.
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 process enables the formation of durable, high-resolution, and efficient piezoelectric actuator assemblies with curved elements that withstand stress and improve the lifetime of MEMS devices by ensuring uniform grain structures and smooth transitions between features.
Implementation Method 1
the top surface of the semiconductor substrate is oxidized to form an oxide layer that covers both the inside of the recess and the planar substrate surface surrounding the recess
Implementation Method 2
A piezoelectric actuator can be formed on one side of the pumping chamber and, in operation, can flex in response to a driving voltage signal to drive fluid along the ink path. The piezoelectric actuator includes a layer of piezoelectric material that changes geometry (i.e., actuates) in response to the driving voltage applied across the piezoelectric layer
Data Source
AI summary
Processes for making a membrane having a curved feature are disclosed. Recesses each in the shape of a reversed, truncated pyramid are formed in a planar substrate surface by KOH etching through a mask. An oxide layer is formed over the substrate surface. The oxide layer can be stripped leaving rounded corners between different facets of the recesses in the substrate surface, and the substrate surface can be used as a profile-transferring substrate surface for making a membrane having concave curved features. Alternatively, a handle layer is attached to the oxide layer and the substrate is removed until the backside of the oxide layer becomes exposed. The exposed backside of the oxide layer includes curved portions protruding away from the handle layer, and can provide a profile-transferring substrate surface for making a membrane having convex curved features.