HEMT Air-Gap Gate Structure for Lower Parasitic Capacitance
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Solution Overview
Problem
Existing high electron mobility transistors (HEMTs) face issues with current gain cut-off frequency decrease due to unfavorable gate parasitic capacitances and threshold voltage instability caused by dielectric charge traps, limiting their high-frequency performance.
Innovation Solution
A high electron mobility transistor with an air gap formed by selectively removing an insulating layer and/or a spacer between the gate structure and the passivation layer through a selective wet etching process, reducing parasitic capacitances and gate leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a continuous insulating layer is used between the gate structure and passivation layer, then the device structure is simple and manufacturing is easy, but gate parasitic capacitances increase and high-frequency performance deteriorates
Solution Approach 1:
The continuous insulating layer is segmented by selectively removing portions to form air gaps between the gate structure and passivation layer. This segmentation reduces gate parasitic capacitances while maintaining manufacturing feasibility through selective wet etching processes.
Solution Approach 2:
Portions of the insulating layer are extracted/removed to create air gaps. This extraction eliminates the harmful dielectric material in specific regions, reducing parasitic capacitances and improving high-frequency performance without requiring complete removal of the insulating layer.
2Stability of the object's composition
If dielectric material is present near the gate structure, then the device structure is complete and stable, but dielectric charge traps cause threshold voltage instability
Solution Approach 1:
Dielectric material is extracted from regions adjacent to the gate structure by selective removal of the insulating layer. This eliminates charge trap sources that cause threshold voltage instability while preserving the overall structural integrity through controlled air gap formation.
Solution Approach 2:
The insulating layer is selectively removed only in specific local regions adjacent to the gate structure, creating air gaps where they are most beneficial for reducing parasitic effects and charge traps, while maintaining insulating coverage in other critical areas for structural stability.
3Device complexity
If the gate structure is fully covered by passivation layer, then the device structure is complete, but parasitic transistor near the gate edge causes gate leakage current
Solution Approach 1:
The insulating layer is selectively removed at the gate edges to create air gaps, extracting the dielectric material that enables parasitic transistor formation. This reduces gate leakage current while maintaining overall device structural completeness through controlled partial removal.
Solution Approach 2:
Air gaps are created locally at the gate structure edges where parasitic transistors form,针对性地 eliminating the harmful effect in the most critical regions while maintaining insulating coverage elsewhere to preserve device structure completeness.
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 air gap reduces gate parasitic capacitances and dielectric charge traps, enhancing the high-frequency performance of HEMTs by increasing current gain cut-off frequency and improving threshold voltage stability.
Implementation Method 1
an air gap formed by selectively removing an insulating layer and/or a spacer between the gate structure and the passivation layer of the HEMT through a selective wet etching process
Data Source
AI summary
A method for forming a high electron mobility transistor includes the steps of forming an epitaxial stack on a substrate, forming a gate structure on the epitaxial stack, forming an insulating layer covering the epitaxial stack and the gate structure, forming a passivation layer on the insulating layer, forming an opening on the gate structure and through the passivation layer to expose the insulating layer, and removing a portion of the insulating layer through the opening to form an air gap between the gate structure and the passivation layer.