Nitride Semiconductor Mesa Structure for Leakage Suppression
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Solution Overview
Problem
Nitride semiconductor transistors with normally-off characteristics face an increase in on resistance when the thickness of the mesa part is increased to enhance threshold voltage, leading to undesirable current paths and increased capacitance, which affects the stability and performance of the device.
Innovation Solution
A semiconductor device structure is developed with a sequential stack of nitride semiconductor layers, including a mesa part and a side part, where the side part extends beyond the gate electrode, suppressing two-dimensional electron gas generation below the mesa part while allowing it below the side part, thereby reducing on resistance and maintaining stable normally-off characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the mesa part is increased to increase the threshold voltage, then the normally-off characteristics are improved, but the on resistance correspondingly increases
Solution Approach 1:
The fourth semiconductor layer is divided into two functional parts: a mesa part positioned below the gate electrode for threshold voltage control, and a side part extending to the outside of the gate electrode for current path management. This segmentation allows the mesa part to be optimized for threshold voltage while the side part maintains low on resistance by preserving 2DEG generation.
Solution Approach 2:
Different regions of the fourth semiconductor layer are given different functions: the mesa part (below the gate) provides 2DEG suppression for threshold voltage control, while the side part (outside the gate) allows 2DEG generation for low on resistance. This local differentiation of function resolves the contradiction between threshold voltage and on resistance.
2Object-generated harmful factors
If the thickness of the mesa part is increased to increase the threshold voltage, then the leakage current is reduced, but the on resistance increases due to undesired current paths
Solution Approach 1:
By segmenting the fourth semiconductor layer into mesa and side parts, the invention creates separate functional zones: the mesa part suppresses 2DEG to reduce leakage current, while the side part extends beyond the gate electrode to maintain 2DEG generation and provide low-resistance current paths, preventing the increase in on resistance.
Solution Approach 2:
The side part extends in the lateral dimension beyond the gate electrode, creating an additional current path that bypasses the high-resistance region under the gate. This dimensional extension provides alternative current flow paths that maintain low on resistance even when the mesa part thickness is increased for leakage current suppression.
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
This configuration effectively reduces leakage current and on resistance while maintaining the generation region of two-dimensional electron gas up to the end of the gate electrode, enhancing the device's performance and stability even when the mesa part's thickness is increased for higher threshold voltage.
Implementation Method 1
two-dimensional electron gas (2DEG) is generated at an interface between a barrier layer and a channel layer
Implementation Method 2
two-dimensional electron gas (2DEG) is generated at an interface between a barrier layer and a channel layer
Implementation Method 3
Generation of the two-dimensional electron gas between the second and third nitride semiconductor layers is suppressed below the mesa part
Data Source
AI summary
Characteristics of a semiconductor device are improved. A semiconductor device includes a sequential stack of a buffer layer, a channel layer, and a barrier layer, and includes a mesa part including a fourth nitride semiconductor layer formed over the stack, and a side part formed on both sides of the mesa part and including a thin film part of the fourth nitride semiconductor layer. Generation of 2DEG is suppressed below the mesa part while being unsuppressed below the side part. In this way, the side part that disables the 2DEG suppression effect is provided on an end portion of the mesa part, thereby a distance from an end portion of the side part to the gate electrode is increased, making it possible to suppress leakage caused by a current path passing through an undesired channel formed between a gate insulating film and the mesa part.