Annular Electrode Structure for Dielectric Stress Decoupling
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Solution Overview
Problem
High-power electronic devices face challenges in withstanding higher voltage differences due to residual mechanical stresses in dielectric layers, particularly when polymeric materials like photosensitive polyimide (PIX) are used, leading to potential damage and reduced performance from thermal expansion and compression differences between the dielectric layer and metal electrodes.
Innovation Solution
The electrode structure incorporates an annular decoupling element with a specific shape and dimensions that distributes thermal expansion forces evenly, reducing stress concentration at the contact region between the metal connection and the electrode, thereby preventing damage to the dielectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dielectric layer thickness is increased to withstand higher voltage differences, then the galvanic insulation capability is improved, but the residual mechanical stress causes wafer deformation and machining difficulties
Solution Approach 1:
The electrode structure is divided into multiple regions: a central active region and an annular decoupling element region. This segmentation allows the dielectric layer to have different functional zones - the central region provides galvanic insulation while the annular region acts as a stress relief zone that prevents wafer deformation during machining
Solution Approach 2:
The annular decoupling element serves as an intermediary structure between the central active electrode and the substrate. It mediates the mechanical stress by providing a transition zone that distributes thermal expansion forces, thereby protecting the central dielectric layer from stress-induced deformation while maintaining the required thickness for high voltage withstand capability
2Reliability
If polymeric materials like PIX are used to form the dielectric layer for higher thickness, then the withstand voltage is improved, but the different CTE between dielectric and metal electrodes causes residual mechanical stress
Solution Approach 1:
The dielectric layer is designed with different local qualities: the central active region uses polymeric material (PIX) optimized for high voltage withstand, while the annular decoupling element region is specifically designed to accommodate thermal expansion differences. This local differentiation allows the structure to withstand high voltages while managing stress through the annular region's geometric design
3Reliability
If the dielectric layer thickness is increased to 40 um using PIX, then the maximum withstand voltage reaches 15-20 kV, but the stress concentration at the contact region may cause damage to the dielectric layer
Solution Approach 1:
The annular decoupling element is designed with curved geometric features that distribute stress evenly across the dielectric layer interface. The curved transition between the central electrode and the annular element eliminates sharp corners and stress concentration points, allowing the thick dielectric layer to maintain its integrity while withstanding high voltages
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 solution effectively reduces stress concentrations in the dielectric layer, enhancing the reliability and performance of galvanic insulation by preventing cracks and maintaining the thickness of the dielectric layer, thus supporting higher voltage differences without degrading the dielectric layer's properties.
Implementation Method 1
Such galvanic insulators are materials with high dielectric strength (for example, higher than 400 kV/mm) that withstand high electrical fields, and therefore high potential differences across them, without undergoing electrical breakdown
Implementation Method 2
in a stack of several materials, the field is shared so that the higher the dielectric constant of the material considered, the lower the electrical field within it
Implementation Method 3
for too high thicknesses of silicon oxide, the effect of the residual mechanical stress (which is markedly compressive with a value of around -300 MPa) transferred to the silicon wafer, causes deformations
Implementation Method 4
the dielectric layer of polymeric material and the metal electrodes usually have respective coefficients of thermal expansion (CTE) that are very different from one another... the thermal cycles of baking of the PIX cause (with each deposition) thermal expansion/compression of the PIX and of the electrodes
Data Source
Figure 1
Figure 2A
Figure 2B~3
AI summary
An electrode structure (1) comprising: a pad (3) of conductive material; and a conductive strip (5) having a first end (5a) physically and electrically coupled to the pad (3), the electrode structure (1) being characterized in that the pad (3) comprises an annular element (7) internally defining a through opening (13), and in that the first end (5a) of the conductive strip (5) is physically and electrically coupled to the annular element (7) by a transition region (19) so that, when the conductive strip (5) undergoes expansion by the thermal effect, a stress spreads from the conductive strip (5) to the annular element (7) by the transition region (19). Main figure: Figure 2B