Stepped Sidewall Electrodes for GaN HEMT High Voltage
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Solution Overview
Problem
Existing III-N semiconductor devices with slant field plates face challenges in reproducibly fabricating small angles required for high voltage operation, leading to difficulties in achieving both low leakage and high breakdown voltages while maintaining low on-resistance and gate capacitance.
Innovation Solution
The design involves an electrode-defining layer with a recess having stepped sidewalls forming different effective angles, allowing for a smaller gate-drain spacing and increased step density, which enables the fabrication of III-N transistors with high voltage capabilities and low on-resistance, achieved through a method involving multiple etching procedures and photoresist redistribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If slant field plates with small angles are used to reduce peak electric field and increase breakdown voltage, then high voltage operation is enabled, but fabrication reproducibility deteriorates
Solution Approach 1:
The field plate is divided into multiple discrete segments or steps rather than a continuous slanted surface. This segmentation allows each step to be fabricated with standard precision while collectively achieving the desired electric field distribution for high voltage operation.
Solution Approach 2:
The solution transitions from a two-dimensional slanted surface to a three-dimensional stepped structure. By adding the vertical dimension with multiple levels, the design achieves the electric field control of a slanted plate while using horizontal steps that are easier to fabricate with reproducible precision.
2Ease of manufacture
If larger gate-drain spacing is used to accommodate slant field plates, then fabrication ease is improved, but device area increases and on-resistance increases
Solution Approach 1:
The field plate structure is segmented into multiple vertical steps rather than requiring a large horizontal spacing. This allows the electric field control function to be achieved within a compact area, reducing both device footprint and on-resistance while maintaining fabrication simplicity.
3Area of moving object
If conventional field plates are used, then device area is reduced, but peak electric field is not sufficiently controlled and breakdown voltage is limited
Solution Approach 1:
The field plate structure implements local quality variations through stepped regions with different heights and positions. Each local region is optimized to control the electric field distribution specifically where needed, achieving superior breakdown voltage control within a compact area.
Solution Approach 2:
By introducing vertical stepping in the field plate structure, the design controls electric field distribution more effectively than conventional flat plates while maintaining a compact device area. The third dimension provides additional control without increasing footprint.
Data Source
AI summary
A III-N semiconductor HEMT device includes an electrode-defining layer on a III-N material structure. The electrode-defining layer has a recess with a first sidewall proximal to the drain and a second sidewall proximal to the source, each sidewall comprising a plurality of steps. A portion of the recess distal from the III-N material structure has a larger width than a portion of the recess proximal to the III-N material structure. An electrode is in the recess, the electrode including an extending portion over the first sidewall. A portion of the electrode-defining layer is between the extending portion and the III-N material structure. The first sidewall forms a first effective angle relative to the surface of the III-N material structure and the second sidewall forms a second effective angle relative to the surface of the III-N material structure, the second effective angle being larger than the first effective angle.