HEMT Cap Layer Structure for Higher Threshold Voltage
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Solution Overview
Problem
Current enhancement-mode high electron mobility transistors (HEMTs) do not fully meet application requirements due to insufficient threshold voltage and reliability issues caused by damage to the barrier layer during cap layer patterning.
Innovation Solution
A body region is formed in the barrier and channel layers directly below the cap layer, with the same conductivity type as the cap layer, and a relatively thin cap layer is used to enhance threshold voltage while minimizing damage during etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick cap layer is used to increase threshold voltage, then the threshold voltage is improved, but the barrier layer is damaged during the patterning process
Solution Approach 1:
The invention divides the cap layer into two distinct parts: a first cap layer with thickness of 5-20 nm that remains after patterning, and a second cap layer with thickness of 20-50 nm that is removed during patterning. This segmentation allows the threshold voltage to be enhanced by the total cap layer thickness while the thin first cap layer protects the barrier layer from damage during the patterning process.
Solution Approach 2:
The first cap layer is formed preliminarily before the second cap layer, and it serves as a protective layer that prevents damage to the barrier layer during subsequent patterning operations. This preliminary protective structure enables the use of a thicker second cap layer for threshold voltage enhancement without compromising barrier layer integrity.
2Ease of manufacture
If the cap layer is patterned, then device structure is defined, but the barrier layer is damaged causing reliability issues
Solution Approach 1:
The first cap layer is formed in advance before the second cap layer, serving as a protective sacrificial layer that prevents barrier layer damage during patterning. This preliminary protective structure enables safe patterning operations while maintaining barrier layer integrity.
Solution Approach 2:
The first cap layer acts as an intermediary protective layer between the patterning process and the barrier layer. It absorbs the mechanical stress and chemical exposure during patterning, preventing direct damage to the barrier layer while still allowing the device structure to be properly defined.
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 solution increases threshold voltage and improves electron mobility and reliability by avoiding damage to the barrier layer, allowing the HEMT to operate with higher voltages and reduced surface defects.
Implementation Method 1
a heat treatment is performed to form a body region in the barrier layer and the channel layer. The body region contains the aforementioned dopant having the conductivity type and is located directly below the cap layer
Data Source
AI summary
A high electron mobility transistor includes a channel layer disposed on a substrate and a barrier layer disposed on the channel layer. A cap layer having a conductivity type is disposed on the barrier layer. A gate electrode is disposed on the cap layer. A source electrode and a drain electrode are disposed on the barrier layer and located on two sides of the gate electrode, respectively. In addition, a body region having the same conductivity type as the cap layer is disposed in the barrier layer and the channel layer and located directly below the cap layer.