Alternating Gold Titanium Electrode for GaN Dielectric Crack Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Dielectric layers in contact with metal in integrated circuits, such as GaN MMICs, experience irreversible deformation and cracking due to thermal cycling, primarily caused by the large thermal expansion coefficient mismatch between gold and gallium nitride, leading to stress on the dielectric film.
Innovation Solution
Incorporating thin layers of titanium throughout the gold layer to stiffen it, creating a laminated structure of alternating gold and titanium layers, which reduces permanent deformation and cracking by using a stiffer metal in conjunction with ductile gold, maintaining electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick layer of pure gold is used as the electrode, then electrical conductivity is improved, but thermal expansion mismatch causes irreversible deformation and cracking of the dielectric layer during thermal cycling
Solution Approach 1:
The single thick gold layer is segmented into multiple alternating layers of gold and titanium. The gold layers maintain electrical conductivity while the titanium layers provide structural stiffness and reduce thermal expansion mismatch. This segmentation allows each material to perform its optimal function without the drawbacks of a monolithic structure.
Solution Approach 2:
A composite electrode structure is created by combining gold and titanium in alternating layers. The composite structure leverages the high electrical conductivity of gold and the high stiffness/low thermal expansion of titanium to achieve both electrical performance and thermal stability simultaneously.
2Reliability
If pure gold is used as the electrode material, then electrical conductivity is maximized, but the ductile gold deforms permanently during thermal cycling, stressing the dielectric film
Solution Approach 1:
The electrode is segmented into alternating layers of ductile gold and stiff titanium. The titanium layers act as structural reinforcements that prevent permanent deformation during thermal cycling, while the gold layers maintain electrical conductivity. The segmented structure allows the ductile and stiff materials to work together synergistically.
Solution Approach 2:
Different regions of the electrode have different local properties: gold layers provide local electrical conductivity while titanium layers provide local structural stiffness. This local differentiation of material properties allows the electrode to simultaneously achieve high conductivity and high resistance to deformation.
3Reliability
If the gold layer is made thicker to ensure conductivity, then electrical performance improves, but the thermal expansion coefficient mismatch with GaN increases, causing more severe deformation
Solution Approach 1:
The thick gold layer is segmented into multiple thinner gold layers separated by titanium layers. This segmentation reduces the cumulative thermal expansion mismatch because the stiff titanium layers interrupt the continuous gold structure, preventing the buildup of thermal stress that would occur in a single thick gold layer.
Solution Approach 2:
The composite structure of alternating gold and titanium layers creates an effective thermal expansion profile that is intermediate between pure gold and GaN. The titanium layers, with their lower thermal expansion coefficient, reduce the overall thermal mismatch with the GaN substrate, thereby reducing thermal stress on the dielectric layer.
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 solution effectively eliminates cracking in dielectric layers by reducing the deformation of the bottom electrode, ensuring the structural integrity of capacitors during thermal cycling.
Implementation Method 1
the thermal expansion coefficient of the gold is much larger that the thermal expansion coefficient of the GaN, and, as a result, the ductile gold is irreversibly deformed during thermal cycling
Data Source
Figure 1
Figure 2
AI summary
A method and structure for reducing cracks in a dielectric (40) in contact with a metal structure (20). The metal structure comprises a first metal layer (26); a second metal layer (30) disposed on, and in contact with the first metal layer, the second metal layer having a higher young' s modular of elasticity than the first metal layer; a third metal layer (32) disposed on, and in contact with the second metal layer, the second metal layer having a higher young's modular of elasticity than the third metal layer. An additional metal (50) is included wherein the dielectric layer is disposed between the metal structure and the additional metal.