GaN Cap Layer Recess Design for Nitride Semiconductor Current Collapse
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Solution Overview
Problem
Current nitride semiconductor transistors experience current collapse due to parasitic capacity issues at high frequencies, which limits their performance in high-frequency and high-output applications.
Innovation Solution
A compound semiconductor device is designed without a field plate electrode, featuring a GaN cap layer with a recess portion and a thick portion between the gate and drain electrodes, where the cap layer thickness is 10 nm or more, and the recess portion is between 2 nm to 6 nm, to reduce current collapse and parasitic capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field plate electrode is provided between the gate electrode and the drain electrode, then current collapse is restrained, but parasitic capacity occurs with respect to the drain electrode
Solution Approach 1:
The invention extracts and removes the field plate electrode from the device structure. By eliminating this component entirely, the parasitic capacity associated with the field plate electrode is removed, while the current collapse restraint function is achieved through alternative means (optimized cap layer thickness and AlGaN layer composition)
2Reliability
If the cap layer thickness is increased to reduce current collapse, then current collapse is restrained more, but the piezo electrical field is mitigated
Solution Approach 1:
The invention applies local quality by creating a non-uniform cap layer thickness distribution. The cap layer has a first thickness in the region between the gate electrode and drain electrode (providing strong current collapse restraint) and a second, greater thickness in the region between the recess portion and drain electrode (maintaining piezo electrical field). This spatial variation in thickness allows simultaneous optimization of both functions
Solution Approach 2:
The cap layer is segmented into distinct thickness regions: a thinner first thickness region and a thicker second thickness region separated by a recess portion. This segmentation allows different functional requirements to be met in different spatial locations within the same layer structure
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 device effectively reduces current collapse and improves high-frequency characteristics by eliminating the need for a field plate electrode, while maintaining desirable device characteristics and minimizing the mitigation of the piezo electrical field.
Implementation Method 1
A HEMT structure having a channel layer made of AlGaN on an electron transit layer made of GaN
Data Source
AI summary
A compound semiconductor device includes: an electron transit layer made of GaN; a channel layer made of AlGaN; a source electrode, a gate electrode and a drain electrode that are provided on the channel layer; a cap layer that is provided at least between the source electrode and the gate electrode and between the gate electrode and the drain electrode and is made of GaN; a recess portion that is provided in the cap layer between the gate electrode and the drain electrode; and a thick portion that is provided in the cap layer between the recess portion and the drain electrode and has a thickness larger than the recess portion.