Elevated Drain Termination for High-Power Transistors
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Solution Overview
Problem
High power transistors with increased unit cell density face breakdown issues due to insufficient gate-to-drain spacing at drain finger electrode ends, leading to unreliable high breakdown voltage performance.
Innovation Solution
The implementation of non-coplanar drain finger termination with curved or tapered ends having increased radius of curvature and extended gate-to-drain spacing, reducing termination electric fields and enhancing breakdown voltage reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If unit cell density is increased to meet higher power requirements, then power capability is improved, but gate-to-drain spacing becomes insufficient leading to reduced breakdown voltage reliability
Solution Approach 1:
The drain finger termination is elevated from the coplanar plane to a higher dimension by forming it over a dielectric layer. This vertical dimensionality change allows the termination to be positioned above the gate-to-drain spacing plane, effectively increasing the electrical spacing without occupying additional lateral space, thus resolving the contradiction between high power density and breakdown voltage reliability
Solution Approach 2:
A dielectric layer is introduced as an intermediary between the drain finger electrode body and the drain finger termination. This intermediary structure enables the termination to be elevated and electrically isolated, providing enhanced gate-to-drain spacing and improving breakdown voltage reliability while maintaining compact device footprint
2Reliability
If gate-to-drain spacing is extended to improve breakdown voltage, then reliability is improved, but device area increases reducing unit cell density
Solution Approach 1:
Instead of extending gate-to-drain spacing in the lateral plane which would increase device area, the solution elevates the drain finger termination vertically above the gate-to-drain spacing plane. This uses the third dimension to achieve enhanced spacing without lateral expansion, maintaining high unit cell density while improving breakdown voltage
3Ease of manufacture
If drain finger termination is made coplanar with main body, then manufacturing is simple, but termination electric fields are high causing breakdown issues
Solution Approach 1:
The drain finger termination is elevated vertically above the coplanar plane by forming it over a dielectric layer. This vertical separation reduces the concentration of termination electric fields at the drain finger ends while maintaining manufacturing feasibility through standard semiconductor fabrication processes
Solution Approach 2:
The dielectric layer acts as an intermediary structure that elevates the drain finger termination, thereby reducing termination electric fields. This intermediary approach manages the harmful electric field concentration without significantly complicating the manufacturing process
Data Source
AI summary
According to an exemplary implementation, a transistor includes drain finger electrodes interdigitated with source finger electrodes. The transistor also includes a current conduction path in a semiconductor substrate between the drain finger electrodes and the source finger electrodes. At least one of the drain finger electrodes has a drain finger electrode end and a drain finger electrode main body, where the drain finger electrode main body is non-coplaner with at least a portion of the drain finger electrode end. The transistor may also include a dielectric material situated between at least a portion of the drain finger electrode end and the semiconductor substrate. The dielectric material can be an increasing thickness dielectric material. The dielectric material can thus elevate the drain finger electrode end over the semiconductor substrate. Further, the drain finger electrode end can have an increased radius of curvature.