Compound Semiconductor Layer Stack with Stress-Reduction Contacts
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Solution Overview
Problem
Compound semiconductor-based devices, such as high-electron-mobility transistors, face challenges due to thermal expansion differences between substrate and epitaxial layers, leading to cracking and breakage during processing.
Innovation Solution
A structure and method involving a layer stack on a substrate with a conductive contact extending vertically through the stack to separate portions, and source and drain ohmic contacts, which are formed to manage stress and reduce the risk of cracking by accommodating thermal expansion differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compound semiconductor layers are grown by heteroepitaxy on a substrate, then the device can exploit material properties such as higher carrier mobility and wider band gap, but thermal expansion differences cause cracking and breakage during processing
Solution Approach 1:
The patent divides the layer stack into multiple discrete layers with different materials and thicknesses. Each layer is optimized to manage stresses differently, with buffer layers, channel layers, and barrier layers serving distinct mechanical and electrical functions. This segmentation allows gradual transition of thermal expansion properties through the stack.
Solution Approach 2:
The patent varies material composition and layer thickness parameters throughout the stack to manage stress. By changing the aluminum content in aluminum-gallium-nitride layers and adjusting layer thicknesses, the thermal expansion coefficient is gradually transitioned to match between substrate and surface layers, reducing thermal stress.
2Reliability
If a conductive contact is added to separate portions of the layer stack, then post-growth cracking is minimized, but device complexity increases
Solution Approach 1:
The conductive contact acts as an intermediary element inserted within the layer stack. This contact serves multiple functions: it provides electrical connectivity, creates a separation plane that prevents crack propagation between device regions, and helps manage thermal stress. The contact is integrated into the fabrication process rather than added as a separate complex component.
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 conductive contact effectively minimizes post-growth cracking and mechanical shape changes, ensuring the stability and integrity of the semiconductor device structure.
Implementation Method 1
differences in the coefficient of thermal expansion between the substrate and the epitaxial compound semiconductor layers on the substrate
Data Source
AI summary
Structures including compound semiconductor-based devices and silicon-based devices integrated on a semiconductor substrate and methods of forming such structures. The structure comprises a layer stack on a substrate, a conductive contact extending in a vertical direction fully through the layer stack to the substrate, and a device structure including a source ohmic contact and a drain ohmic contact. The layer stack including a plurality of semiconductor layers each comprising a compound semiconductor material, the conductive contact is arranged in the layer stack to separate a first portion of the layer stack from a second portion of the layer stack, and the source ohmic contact and the drain ohmic contact have a contacting relationship with at least one of the plurality of semiconductor layers of the first portion of the layer stack.