GaN Transistor Field Control for High-Voltage THz Operation
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Solution Overview
Problem
Current THz devices face challenges in achieving high power and frequency operation due to high access resistances, rapid degradation of cutoff frequencies with increasing drain bias, and low operating voltages, which limit their efficiency and effectiveness in the terahertz frequency range.
Innovation Solution
The use of two additional independently biased electrodes to control the electric field and space-charge close to the gate edges in a group III nitride-based device, reducing effective gate length extension and increasing electron velocity, while also employing capacitively coupled contacts to minimize contact resistance and enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional HEMT structures are used to achieve high electron velocity for THz operation, then cutoff frequencies can reach THz range, but access resistances become excessively high and operating voltages become too low
Solution Approach 1:
The source and drain contacts are segmented into multiple fingers that interdigitate with the gate, distributing the current flow paths and reducing the effective access resistance while maintaining high electron velocity in the channel
Solution Approach 2:
The contact structure transitions from a simple planar configuration to a three-dimensional interdigitated finger structure, utilizing vertical stacking and lateral arrangement to reduce current crowding and access resistance without increasing the device footprint
2Power
If drain bias is increased to improve output power, then operating power increases, but cutoff frequencies rapidly degrade due to short-channel effects
Solution Approach 1:
The gate structure is designed with extended sidewalls and optimized doping profiles that preemptively counteract the formation of high-field regions and hot carriers before they can cause significant cutoff frequency degradation, allowing higher drain biases to be applied
Solution Approach 2:
The device utilizes changes in material composition and doping concentrations in the channel and barrier layers to modify the electric field distribution, enabling higher operating voltages without the typical short-channel degradation of cutoff frequency
3Speed
If gate length is reduced to increase electron velocity, then cutoff frequency increases, but effective gate length increases due to space-charge region expansion at high drain bias
Solution Approach 1:
The gate sidewalls are extended and doped regions are pre-configured to create field-plate effects that preemptively control the space-charge region expansion, preventing effective gate length increase before it occurs during high drain bias operation
Solution Approach 2:
Field-plate structures and doped barrier layers act as intermediary regions that mediate between the gate and drain, controlling the electric field distribution and preventing space-charge region penetration into the active channel length
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
This approach enables terahertz-range cutoff and maximum frequencies of operation at relatively high drain voltages, significantly improving the device's performance by increasing electron velocity and minimizing space-charge penetration, thus enabling high-power THz sources.
Implementation Method 1
The use of two additional independently biased electrodes to control the electric field and space-charge close to the gate edges
Implementation Method 2
control the electric field and space-charge close to the gate edges
Implementation Method 3
employing capacitively coupled contacts to minimize contact resistance
Data Source
AI summary
A group III nitride-based transistor capable of achieving terahertz-range cutoff and maximum frequencies of operation at relatively high drain voltages is provided. In an embodiment, two additional independently biased electrodes are used to control the electric field and space-charge close to the gate edges.