GaN Sensor Electrostatic Control via Subthreshold 2DEG Depletion
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Solution Overview
Problem
Gallium-Nitride (GaN) based sensors face challenges in achieving high sensitivity to external influences due to difficulties in controlling the 2DEG channel dimensions and the complexity of fabricating devices with open surfaces and Schottky gates, which limits their sensitivity to small gas or liquid concentrations and increases fabrication complexity.
Innovation Solution
An electrostatically controlled sensor with a heterostructure of an AlGaN layer over a GaN layer, featuring a 2DEG channel at the upper surface, where source and drain contacts are coupled to the channel, and gate electrodes are separated by small gaps to create a subthreshold operating regime, enhancing sensitivity to external influences like gases, liquids, and UV irradiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the AlGaN layer is intentionally thinned in the sensing area to increase sensitivity, then the sensitivity of the device is increased, but the control of the recessed region thickness becomes difficult and fabrication complexity increases
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the gate electrode and the AlGaN layer. This dielectric layer enables precise control of the electric field in the sensing area without requiring direct manipulation of the AlGaN thickness, thereby maintaining sensitivity while simplifying fabrication control
Solution Approach 2:
The invention changes the control parameter from direct AlGaN layer thickness to dielectric layer thickness and gate voltage. By controlling the dielectric layer thickness and applying appropriate gate voltages, the electric field distribution is precisely controlled, achieving high sensitivity without difficult thickness control of the recessed region
2Ease of operation
If Schottky gates penetrating the GaN bulk are used to create open surface sensors, then electrostatic control is achieved, but the sensing area becomes much smaller than the channel area and fabrication complexity increases
Solution Approach 1:
The invention transitions from three-dimensional penetrating Schottky gates to two-dimensional planar gate electrodes separated by gaps. This dimensional change allows the gate electrodes to extend substantially entirely between source and drain contacts, maximizing the sensing area while maintaining electrostatic control through the dielectric layer
3Measurement precision
If the device is operated in subthreshold regime to maximize sensitivity, then the sensitivity to external influences is maximized, but the threshold voltage decreases and requires precise control
Solution Approach 1:
The invention makes the threshold voltage dynamically adjustable through gate voltage control rather than being fixed by structural parameters alone. By applying different gate voltages, the device can be tuned into or out of the subthreshold regime, providing flexibility in optimizing sensitivity without requiring precise fixed threshold voltage control during fabrication
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 sensor operates efficiently in a subthreshold mode, maximizing sensitivity to external influences while being inexpensive to fabricate and capable of operating across a wide temperature range, from -40°C to 500°C, with low power consumption and high signal-to-noise ratio.
Implementation Method 1
The 2DEG channel originates from piezoelectric polarization that is superimposed by electrical charges from an aluminum gallium-nitride (AlGaN) surface formed over a GaN layer
Implementation Method 2
When a voltage is applied across the source and drain contacts, and an appropriate voltage is applied to the gate electrodes, the portions of the 2DEG channel located under the gate electrodes are fully depleted, and the portions of the 2DEG channel located under the one or more gaps between the gate electrodes are partially depleted
Data Source
AI summary
An electrostatically controlled sensor includes a GaN/AlGaN heterostructure having a 2DEG channel in the GaN layer. Source and drain contacts are electrically coupled to the 2DEG channel through the AlGaN layer. A gate dielectric is formed over the AlGaN layer, and gate electrodes are formed over the gate dielectric, wherein each gate electrode extends substantially entirely between the source and drain contacts, wherein the gate electrodes are separated by one or more gaps (which also extend substantially entirely between the source and drain contacts). Each of the one or more gaps defines a corresponding sensing area between the gate electrodes for receiving an external influence. A bias voltage is applied to the gate electrodes, such that regions of the 2DEG channel below the gate electrodes are completely depleted, and regions of the 2DEG channel below the one or more gaps in the direction from source to drain are partially depleted.