GaN Unit Cell Threshold Segmentation for Smoother Turn-On Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High power semiconductor devices, particularly those using gallium nitride based materials, exhibit sharp turn-on behavior leading to significant variance in third order transconductance, generating third order intermodulation products that degrade communication system performance.
Innovation Solution
The semiconductor devices are designed with varying threshold voltages across different regions or by applying different gate voltages to unit cell transistors, smoothing the turn-on behavior by ensuring different portions of the 2DEG channel turn on at different current levels, achieved through varying thicknesses of the gallium nitride based barrier layer, doping concentrations, or using a voltage divider circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform threshold voltage is used across all unit cell transistors, then device simplicity is maintained, but sharp turn-on behavior occurs leading to high third order transconductance and intermodulation products
Solution Approach 1:
The patent applies local quality by introducing threshold voltage variations across different unit cell transistors. Specifically, different subsets of unit cell transistors are assigned different threshold voltage values (e.g., Vth1, Vth2, Vth3) through modifications to the barrier layer thickness, doping concentrations, or gate structure in localized regions. This causes different portions of the 2DEG channel to turn on at different current levels, smoothing the overall device turn-on behavior and reducing third order transconductance peaks that generate intermodulation products.
2Reliability
If threshold voltage variation is introduced to smooth turn-on behavior, then linearity is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the semiconductor device into multiple subsets of unit cell transistors, where each subset has a distinct threshold voltage value. For example, the device is divided into subsets with threshold voltages Vth1, Vth2, and Vth3, achieved by creating discrete regions with different barrier layer thicknesses or doping profiles. This segmentation allows independent control of turn-on characteristics for each subset, smoothing the overall transfer characteristic and improving linearity while maintaining a systematic fabrication approach.
3Reliability
If different barrier layer thicknesses are used to create threshold voltage variation, then turn-on smoothing is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by systematically varying key device parameters to achieve threshold voltage differentiation. This includes modifying barrier layer thickness (e.g., varying AlGaN layer thickness from 3nm to 9nm in different regions), changing doping concentrations in the barrier or channel layers, or adjusting gate metal composition. These parameter variations are implemented through controlled fabrication processes such as selective epitaxial growth, ion implantation, or metal deposition, allowing precise threshold voltage tuning while maintaining manufacturability.
Data Source
Figure 1
Figure 2~3
Figure 4A~4C
AI summary
A semiconductor device includes a plurality of unit cell transistors on a common semiconductor structure, the unit cell transistors electrically connected in parallel, and each unit cell transistor including a respective gate finger. Respective threshold voltages of first and second of the unit cell transistors differ by at least 0.1 volts and/or threshold voltages of first and second segments of a third of the unit cell transistors differ by at least 0.1 volts.