Nitride Transistors for Millimeter Wave Power Density
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Solution Overview
Problem
Current wide bandgap transistors face challenges in achieving high power density and efficiency for millimeter wave operation due to parasitic capacitances and reduced gain associated with field plates, making it difficult to operate effectively at frequencies exceeding 30 GHz.
Innovation Solution
A field effect transistor design incorporating a Group III-nitride channel layer with a spacer layer, a gate contact, and a lower field plate extending across the spacer layer, along with a dual field plate configuration connected to the source contact, which enhances power density and power added efficiency by reducing gate-to-drain feedback capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a field plate is added to enhance breakdown voltage, then power capability is improved, but parasitic capacitances increase and gain is reduced
Solution Approach 1:
The field plate structure is segmented into multiple sections with different geometries and positions. The field plate is divided into a first field plate portion and a second field plate portion, each with optimized dimensions and locations to provide breakdown voltage enhancement while minimizing parasitic capacitance effects at millimeter wave frequencies.
Solution Approach 2:
Different portions of the field plate are designed with locally optimized properties. The field plate geometry, thickness, and material composition are varied in different regions to achieve optimal electric field distribution for breakdown voltage enhancement while controlling parasitic capacitances in specific areas where they would most affect millimeter wave performance.
2Speed
If gate dimensions are reduced to increase switching speed for millimeter wave operation, then frequency response is improved, but power output is reduced
Solution Approach 1:
The solution moves from optimizing only gate length to a multi-dimensional approach that includes gate width, field plate geometry, layer thicknesses, and vertical electric field distribution. By optimizing across multiple dimensions, the invention achieves both fast switching for millimeter wave operation and sufficient power output through enhanced breakdown voltage in the vertical dimension.
Solution Approach 2:
The invention employs composite material structures including nitride semiconductor layers with different bandgaps (GaN, AlGaN), various dielectric materials for the field plate and spacer layers, and optimized metal contacts. This composite structure enables simultaneous achievement of high switching speed and power output by leveraging the unique properties of each material in the stack.
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 design achieves a power density of greater than 5 W/mm and power added efficiency of over 30% at frequencies of at least 30 GHz, with some embodiments reaching 8 W/mm and 35% efficiency at 35 GHz, demonstrating improved performance for millimeter wave operations.
Implementation Method 1
a gate contact on the Group III-nitride channel layer and configured to modulate a conductivity of the channel layer when a sufficient voltage is applied to the gate contact
Implementation Method 2
A lower field plate is electrically connected to the gate contact and extends across the spacer layer a distance LFD toward the drain contact
Implementation Method 3
A source field plate is electrically connected to the gate contact and extends across the spacer layer a distance LFS toward the source contact
Data Source
AI summary
Field effect transistors having a power density of greater than 5 W/mm when operated at a frequency of at least 30 GHz are provided. The power density of at least 5 W/mm may be provided at a drain voltage of 28 V. Transistors with a power density of at least 8 W/mm when operated at 40 GHz at a drain voltage of 28 V are also provided.