Shielded Gate Trench Superjunction MOSFETs With Lower Rsp and Qgd
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional power MOSFETs face challenges in achieving low specific on-resistance (Rsp) and low gate-to-drain capacitance (Cgd) for breakdown voltages higher than 300V, as existing superjunction (SJ) and shielded gate trench (SGT) structures have limitations in optimizing these parameters simultaneously.
Innovation Solution
The development of shielded gate trench (SGT) superjunction (SJ) MOSFETs with multiple stepped epitaxial (MSE) structures in both SGT and SJ regions, incorporating a first type MSE structure in the oxide charge balance (OCB) region and a second type MSE structure in the SJ region, along with a multiple stepped oxide (MSO) structure, to reduce Rsp and enhance avalanche capability without degrading breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SGT or SJ MOSFET structures are used for breakdown voltage higher than 300V, then device simplicity is maintained, but specific on-resistance increases and gate-to-drain capacitance remains high
Solution Approach 1:
The patent merges the SGT structure and SJ structure into a hybrid configuration where the drain region employs SJ columns (alternating doped and undoped regions) for low on-resistance, while the gate trench structure incorporates shielding electrodes and oxide layers to reduce gate-to-drain capacitance. This combination allows the device to achieve both low Rsp and low Cgd for breakdown voltages above 300V
Solution Approach 2:
The patent applies different structural characteristics to different regions: the drain region uses superjunction columns with alternating doping for low resistance, the gate trench uses shielding electrodes for capacitance reduction, and the interface region uses oxide charge balance for field control. Each region is optimized locally to contribute to overall performance
2Reliability
If conventional SGT or SJ MOSFET structures are used for breakdown voltage higher than 300V, then device simplicity is maintained, but gate-to-drain capacitance increases
Solution Approach 1:
The patent extracts the gate-to-drain capacitance problem by introducing a shielding electrode within the gate trench that is electrically connected to the gate. This shielding electrode creates a field shielding effect that reduces the capacitive coupling between the gate and drain, effectively extracting the harmful capacitance from the device performance
Solution Approach 2:
The patent introduces oxide layers (such as silicon oxide) as intermediary materials between the gate electrode and the semiconductor regions. These oxide layers serve as mediators that provide electrical insulation and field control, reducing the direct capacitive interaction between the gate and drain while maintaining the necessary electrical fields for device operation
3Object-generated harmful factors
If high doping concentration is used in drift region to reduce specific on-resistance, then Rsp decreases, but breakdown voltage degrades
Solution Approach 1:
The patent segments the drift region into alternating doped columns and undoped columns in the superjunction structure. The doped columns provide low resistance paths for current flow, while the undoped columns maintain high breakdown voltage by preventing premature avalanche breakdown. This segmentation allows both low Rsp and high BV to coexist in the same drift region
4Ease of manufacture
If conventional structures are used, then manufacturing process is simple, but high electric field peaks occur in channel region reducing avalanche capability
Solution Approach 1:
The patent introduces a vertical dimension to field control by stacking multiple oxide layers with different thicknesses in the gate trench (multiple stepped oxide structure). The oxide layers have varying thicknesses decreasing stepwise from the gate electrode toward the drain, creating a graded field distribution that eliminates peak electric fields in the channel region while maintaining avalanche capability
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 configuration significantly reduces specific on-resistance and avoids high electric field peaks in the channel region, enhancing the avalanche capability while maintaining or improving breakdown voltage performance.
Implementation Method 1
the shielded gate electrode is insulated from the epitaxial layer by a first insulating film, the gate electrode is insulated from the epitaxial layer by a gate oxide
Implementation Method 2
the shielded gate electrode and the gate electrode are insulated from each other by an (Inter-Poly Oxide) IPO film
Implementation Method 3
the epitaxial layer in the OCB region has a first type MSE layers with different doping concentrations decreasing stepwise in a direction from a bottom of the shielded gate electrode toward the body regions
Implementation Method 4
a SJ region below the OCB region including alternating first doped columns of the first conductivity type and second doped columns of the second conductivity type arranged in parallel
Data Source
AI summary
The present invention introduces new shielded gate trench (SGT) superjunction (SJ) MOSFETs having a first type multiple stepped epitaxial (MSE) structure in oxide charge balance (OCB) region and a second type MSE structure in SJ region for improved specific on-resistance Rsp and gate-to-drain charge Qgd. The two-type MSE structures can increase the average doping concentration in drift regions of the SGT SJ MOSFETS, as a result, lower Rsp and higher avalanche capability could be achieved without degrading breakdown voltage.