Nitride Semiconductor Passivation Structure for Lower Gate Capacitance
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Solution Overview
Problem
Current nitride semiconductor devices face challenges in reducing source-gate capacitance and mitigating electric field concentration, which affects the performance of high-electron-mobility transistors (HEMTs).
Innovation Solution
The nitride semiconductor device incorporates a passivation layer with specific thickness variations and structural features, including a first part with a greater thickness than a second part, and a field plate electrode that mitigates electric field concentration by covering the gate layer, reducing source-gate capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional passivation layer structure is used, then the device structure is simple, but the source-gate capacitance is high and electric field concentration is severe
Solution Approach 1:
The passivation layer is segmented into multiple distinct layers: a first passivation layer with a first dielectric constant and a second passivation layer with a second dielectric constant. This segmentation allows each layer to contribute differently to capacitance reduction, with the first layer providing primary insulation and the second layer providing enhanced field control, thereby reducing source-gate capacitance while maintaining manageable structural complexity
Solution Approach 2:
Different regions of the passivation structure are assigned different dielectric properties. The first passivation layer has a lower dielectric constant in regions closer to the gate to reduce capacitance, while the second passivation layer has a higher dielectric constant to provide field control. This local differentiation of material properties optimizes the balance between capacitance reduction and field management without requiring complete structural redesign
2Reliability
If a conventional field plate structure is used, then the manufacturing process is simple, but the electric field concentration at gate edges is severe
Solution Approach 1:
The field plate structure extends the gate electrode in the vertical dimension by adding a field plate layer that protrudes beyond the gate edge. This dimensional extension creates a gradual field transition zone that mitigates electric field concentration at the gate edges. The field plate is positioned in the third dimension (vertical) rather than merely expanding the gate area horizontally, providing effective field control while maintaining compatibility with standard fabrication processes
3Reliability
If the passivation layer thickness is uniform, then the manufacturing process is simple, but the electric field distribution is not optimized
Solution Approach 1:
The passivation structure employs local quality variation through multiple layers with different dielectric constants positioned at different locations. The first passivation layer with lower dielectric constant is applied in regions where capacitance reduction is prioritized, while the second passivation layer with higher dielectric constant is applied where field control is needed. This local differentiation optimizes electric field distribution without requiring complex non-uniform thickness control within single layers
Solution Approach 2:
The passivation structure uses composite materials consisting of multiple dielectric layers with different properties. The first passivation layer and second passivation layer are combined to create a composite structure that leverages the advantages of each material: the lower dielectric constant material for capacitance reduction and the higher dielectric constant material for field control. This composite approach achieves optimized field distribution while using standard dielectric materials and fabrication techniques
Data Source
AI summary
A nitride semiconductor device includes a passivation layer, which covers a gate layer, and a field plate electrode, which is arranged on the passivation layer. The gate layer includes a gate layer main body and a drain-side extension. The passivation layer includes a first part overlapping both the drain-side extension and the field plate electrode in plan view, a second part continuous with the first part and located between the drain-side extension and the drain opening, and a first step located in a region including a boundary of the first part and the second part. The first part has a first thickness from the upper step surface to an upper surface of the drain-side extension. The second part has a second thickness from the lower step surface to an upper surface of the electron supply layer. The first thickness is greater than the second thickness.