SiC MIS Transistor Barrier Layer Reduces ON Resistance
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Solution Overview
Problem
SiC power devices experience increased ON resistance due to carrier recombination in the n-type drift region, leading to extended crystal defects during switching operations, which affects breakdown voltage and device performance.
Innovation Solution
A SiC field effect transistor with a Metal Insulator Semiconductor (MIS) structure, including a source region, body region, drift region, and a gate electrode with a barrier forming layer that forms a junction barrier lower than the diffusion potential of the body diode, reducing current flow through the body diode and minimizing carrier migration between the body and drift regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current flows through the body diode during switching operations, then counter electromotive voltage is consumed, but carrier recombination occurs in the n-type drift region causing increased ON resistance
Solution Approach 1:
The patent introduces a barrier forming layer as an intermediary component between the body region and drift region. This layer creates a selective barrier that mediates carrier flow: it blocks holes from reaching the drift region during body diode conduction, preventing electron-hole recombination, while still allowing the body diode to function for consuming counter electromotive voltage. The barrier forming layer thus acts as a selective gate that separates the beneficial function (voltage consumption) from the harmful effect (carrier recombination and ON resistance increase).
2Reliability
If holes migrate from the p-type body region to the n-type drift region, then body diode rectification function is achieved, but electron-hole recombination extends SiC crystal defects
Solution Approach 1:
The barrier forming layer serves as a selective intermediary that allows the body diode to maintain its rectification function while preventing harmful carrier migration. During reverse bias, the barrier layer permits hole flow for rectification but blocks holes from reaching the drift region where they would cause recombination. This selective blocking action preserves the beneficial rectification effect while eliminating the harmful crystal defect extension.
3Productivity
If the junction barrier of the barrier forming layer is lower than the diffusion potential of the body diode, then current preferentially flows through the barrier forming layer, but this requires precise control of barrier height
Solution Approach 1:
The patent employs parameter changes by controlling the impurity concentration, material composition, and thickness of the barrier forming layer to achieve the desired barrier height. By adjusting these physical parameters during fabrication, the barrier height can be precisely controlled to be lower than the body diode's diffusion potential, ensuring preferential current flow through the barrier layer while maintaining manufacturability through standard semiconductor processing techniques.
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 MIS structure reduces recombination of carriers, suppresses the extension of SiC crystal defects, and maintains proper breakdown voltage while lowering ON resistance, enabling higher current flow and improved device performance.
Implementation Method 1
a barrier forming layer provided in contact with the drift region to form a junction barrier by the contact with the drift region, the junction barrier being lower than a diffusion potential of a body diode
Implementation Method 2
the junction barrier being lower than a diffusion potential of a body diode defined by a junction (pn junction) between the body region and the drift region
Implementation Method 3
a 'Metal Insulator Semiconductor' (hereinafter 'MIS') transistor structure including a source region of a first conductivity type provided in the SiC semiconductor layer, a body region of a second conductivity type provided in the SiC semiconductor layer in contact with the source region
Implementation Method 4
a parasitic diode (body diode) defined by a pn junction between a p-type body region and an n-type drift region
Implementation Method 5
This prevents a high counter electromotive voltage from being applied to the switching device
Implementation Method 6
when the current flows with holes migrating from the p-type body region of the pn body diode to the n-type drift region, a multiplicity of carrier electrons are liable to be recombined with the holes migrating from the p-type body region in the n-type drift region
Implementation Method 7
This may result in extended SiC crystal defects due to energy generated by the recombination
Data Source
AI summary
A SiC field effect transistor includes: a SiC semiconductor layer; and a MIS transistor structure including a first conductivity type source region in the semiconductor layer, a second conductivity type body region in the semiconductor layer in contact with the source region, a first conductivity type drift region in the semiconductor layer in contact with the body region, a gate electrode opposed to the body region with a gate insulation film interposed between the electrode and the body region for forming a channel in the body region to cause electric current to flow between the drift region and the source region, and a barrier forming layer in contact with the drift region to form a junction barrier by the contact with the drift region, the junction barrier being lower than a diffusion potential of a body diode defined by a junction between the body region and the drift region.