III-V Transistor Breakdown Voltage via Buried Passivation
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Solution Overview
Problem
III-V compound semiconductor-based transistors face challenges in achieving high breakdown voltage due to the shape and size of the depletion region, which affects the surface electric field and device performance.
Innovation Solution
A novel structure for III-V compound semiconductor transistors is introduced, featuring a restricted carrier channel layer formed by selectively removing portions of the donor-supply layer and filling the space with passivation material, reducing current flow and increasing breakdown voltage. This structure includes a buried passivation material that creates non-conductive patches in the carrier channel layer, reducing the effective width and increasing the breakdown voltage threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a large surface electric field is formed around the gate edge to enable power applications, then high voltage handling capability is improved, but breakdown voltage decreases due to electric field concentration
Solution Approach 1:
A field plate structure is introduced as an intermediary element between the gate and the drain region. The field plate is positioned over the passivation layer and extends beyond the gate edge, acting as a mediator to redistribute the electric field. This intermediary structure reduces the concentration of electric field at the gate edge while maintaining the overall high voltage handling capability, thereby improving breakdown voltage without sacrificing power handling capability.
Solution Approach 2:
The patent modifies the electric field distribution parameters by changing the geometry and position of the field plate. By adjusting the field plate's width, height, and lateral extension beyond the gate, the electric field parameters (density, distribution pattern) are optimized. This parameter change allows the device to maintain high voltage handling while reducing peak electric field concentration that causes breakdown.
2Reliability
If a metallic field plate is added to modulate surface electric field distribution and enhance breakdown voltage, then breakdown voltage is improved, but device complexity increases
Solution Approach 1:
The field plate structure serves multiple functions simultaneously: it acts as an electric field modulator to improve breakdown voltage, serves as part of the overall gate structure for voltage application, and provides a platform for further optimizations. By making the field plate multi-functional, the patent reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving the desired breakdown voltage enhancement.
Solution Approach 2:
The field plate is merged with the existing gate structure and passivation layer system. Rather than being a completely separate component, the field plate integrates with the gate electrode and the overlying passivation layer, forming a unified structure. This merging approach reduces the number of discrete parts and simplifies the overall device architecture while still achieving the electric field modulation necessary for improved breakdown voltage.
3Reliability
If the carrier channel layer is restricted by removing donor-supply layer portions and filling with passivation material, then breakdown voltage threshold is increased, but on-state current is reduced
Solution Approach 1:
The patent applies local quality modification by selectively removing donor-supply layer portions only in specific regions (creating through-holes or recesses) and filling those specific locations with passivation material. This localized modification restricts the carrier channel in specific areas to increase breakdown voltage threshold, while leaving other regions intact to maintain adequate on-state current flow. The local quality change allows differentiation between regions requiring high breakdown protection and regions requiring current conduction.
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 proposed structure enhances the breakdown voltage threshold while maintaining high electron mobility, reducing on-state current and improving transistor performance by modulating the surface electric field and increasing resistance between the drain and source.
Implementation Method 1
filling the space with passivation material, reducing current flow and increasing breakdown voltage
Implementation Method 2
The field plate modulates the surface electric field distribution and enhances the breakdown voltage
Data Source
AI summary
A transistor includes a first layer over a substrate. The transistor also includes a second layer over the first layer. The transistor further includes a carrier channel layer at an interface of the first layer and the second layer. The transistor additionally includes a gate structure, a drain, and a source over the second layer. The transistor also includes a passivation material in the second layer between an edge of the gate structure and an edge of the drain in a top-side view. The carrier channel layer has a smaller surface area than the first layer between the edge of the gate structure and the edge of the drain in the top-side view.