T-Shaped HEMT Gate Structure With Air Gap Capacitance Isolation
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Solution Overview
Problem
High Electron Mobility Transistors (HEMT) devices face gate-drain and gate-source capacitance issues that affect their performance metrics such as ft and fmax, limiting their operational efficiency.
Innovation Solution
The introduction of a t-shaped gate structure with a horizontal top portion and a substantially vertical stem portion, featuring an air gap with a curved surface under the horizontal portion, which is manufactured using photolithographic processes and etching techniques to enhance device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional gate structure is used in HEMT devices, then the device structure is simple and easy to manufacture, but gate-drain and gate-source capacitance issues occur that affect device performance
Solution Approach 1:
The gate structure is segmented into distinct portions: a horizontal gate portion and a vertical stem portion extending into the channel region. This segmentation allows the gate to be divided into functional zones that reduce parasitic capacitance while maintaining control over the channel, directly addressing the capacitance performance issue without excessive complexity
Solution Approach 2:
The gate structure transitions from a conventional two-dimensional planar configuration to a three-dimensional T-shaped structure by adding a vertical stem portion that extends downward into the channel region. This dimensional change enables reduced capacitance by separating gate regions in the vertical dimension while maintaining manufacturing feasibility through standard semiconductor processing techniques
2Productivity
If the gate structure is extended vertically into the channel region, then capacitance is reduced and frequency performance is enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
The vertical stem portion of the gate is formed preliminarily during the standard gate fabrication sequence by extending the gate electrode deposition and patterning processes into the channel region before final gate contact formation. This preliminary action integrates the capacitance-reducing feature into the existing manufacturing flow without requiring separate complex fabrication steps
Solution Approach 2:
The vertical stem portion serves multiple functions: it reduces gate-drain and gate-source capacitance, provides additional gate control over the channel region, and maintains compatibility with standard HEMT fabrication processes. This multi-functionality achieves frequency performance enhancement without proportionally increasing manufacturing complexity
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to gate structures and methods of manufacture. The structure includes: a gate structure comprising a horizontal portion and a substantially vertical stem portion; and an air gap surrounding the substantially vertical stem portion and having a curved surface under the horizontal portion.