GaN MIS Sensor Structure for Stable Threshold Voltage Control
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Solution Overview
Problem
AlGaN/GaN sensors face challenges in achieving controlled and stable threshold voltage due to non-uniformities in manufacturing processes, particularly related to gate metal edge profiles, 2DEG carrier density control, and sensor condition regeneration, which affect sensitivity and reliability in sensing applications.
Innovation Solution
A method for fabricating AlGaN/GaN sensors with a metal-insulator-semiconductor (MIS) high electron-mobility transistor (HEMT) structure, involving the formation of a gate dielectric layer, metal gate electrodes, and dielectric spacers to control the threshold voltage and reduce current leakage, along with an etch stop layer for precise thickness control of the AlGaN barrier layer and a 2DEG resistor for thermal refresh.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a gate electrode is added to increase sensitivity to external influences, then sensitivity is improved, but device complexity increases
Solution Approach 1:
The gate electrode structure is segmented into multiple functional layers: a gate dielectric layer for electrical isolation, a metal gate electrode for field control, and dielectric spacers for lateral isolation. This segmentation allows each component to perform its specific function independently, achieving high sensitivity while maintaining manageable device complexity through modular design.
2Reliability
If dielectric spacers are formed to reduce current leakage between gate and 2DEG, then reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
Dielectric spacers are formed preliminarily during the fabrication process by depositing dielectric material conformally on the gate electrode structure and then performing anisotropic etching. This preliminary formation of isolation structures ensures that current leakage paths are blocked before device operation, achieving high reliability while the standardized process steps keep manufacturing precision requirements within achievable limits.
3Manufacturing precision
If AlGaN barrier layer thickness is controlled precisely to control 2DEG carrier density, then threshold voltage control is improved, but manufacturing complexity increases
Solution Approach 1:
Instead of requiring precise control of the entire AlGaN barrier layer thickness throughout the structure, the invention applies partial action by focusing thickness control only in critical regions. The etch stop layer is positioned at a specific depth to ensure the AlGaN barrier layer has the correct thickness where it interfaces with the 2DEG channel, while other regions can have varying thicknesses. This approach achieves the necessary threshold voltage control without the excessive complexity of controlling the entire layer uniformly.
4Manufacturing precision
If an etch stop layer is added to control AlGaN barrier layer thickness, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
An etch stop layer is introduced as an intermediary layer between the AlGaN barrier layer and the underlying GaN buffer. This intermediary layer has distinct etching properties that allow selective removal of the AlGaN barrier layer to a precise depth. The etch stop layer acts as a physical reference plane during fabrication, enabling accurate thickness control of the AlGaN barrier layer without requiring complex in-situ monitoring, thus improving manufacturing precision while adding only moderate device complexity.
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 approach results in a stable and sensitive AlGaN/GaN sensor with improved threshold voltage control, reduced current leakage, and enhanced reliability, enabling effective monitoring of external influences in real-time without manufacturing complexity.
Implementation Method 1
passing a current through a two-dimensional electron gas (2DEG) resistor to generate heat for thermal refresh of the sensor
Data Source
AI summary
A method fabricating a GaN based sensor including: forming a gate dielectric layer over a GaN hetero-structure including a GaN layer formed over a substrate and a first barrier layer formed over the GaN layer; forming a first mask over the gate dielectric layer; etching the gate dielectric layer and the first barrier layer through the first mask, thereby forming source and drain contact openings; removing the first mask; forming a metal layer over the gate dielectric layer, wherein the metal layer extends into the source and drain contact openings; forming a second mask over the metal layer; etching the metal layer, the gate dielectric layer and the GaN heterostructure through the second mask, wherein a region of the GaN heterostructure is exposed; and thermally activating the metal layer in the source and drain contact openings. The gate dielectric may exhibit a sloped profile, and dielectric spacers may be formed.