Semiconductor Field Plate Trench Insulation for Capacitance Reduction
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Solution Overview
Problem
Conventional power semiconductor devices face a trade-off between on-resistance and input capacitance, leading to a high product that limits the figure of merit, primarily due to increased inter-electrode capacitance between the gate and field plate electrodes, which hinders achieving both high withstand voltage and low switching loss.
Innovation Solution
The semiconductor device incorporates a vertical field plate structure with a field plate electrode buried in the trench through a thick insulating film and a gate electrode in the upper trench portion, using a second insulating film to reduce the inter-electrode capacitance by thermally oxidizing the upper portion of the field plate electrode, creating a thinner gate insulating film and a thicker second insulating film to minimize capacitance between the gate and field plate electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a field plate electrode is buried into a trench through a thick field plate insulating film to achieve high withstand voltage, then the withstand voltage is improved, but the inter-electrode capacitance between the gate electrode and field plate electrode increases, leading to increased input capacitance
Solution Approach 1:
The patent divides the insulating film structure into two distinct segments: a first insulating film (field plate insulating film) between the field plate electrode and second semiconductor layer, and a second insulating film (gate insulating film) between the gate electrode and field plate electrode. This segmentation allows each insulating film to be optimized independently for its specific function, resolving the contradiction between withstand voltage and input capacitance.
Solution Approach 2:
The patent applies different quality characteristics to different parts of the insulating film structure. The first insulating film is designed with specific thickness and material properties to optimize field plate function and withstand voltage, while the second insulating film is designed with different properties to minimize inter-electrode capacitance. This local differentiation of properties resolves the technical contradiction.
2Quantity of substance
If the inter-electrode capacitance between gate electrode and field plate electrode is reduced to decrease input capacitance, then the figure of merit is improved, but the withstand voltage capability may be compromised
Solution Approach 1:
By segmenting the insulating structure into two separate films with distinct functions, the patent enables the first insulating film to maintain withstand voltage capability while the second insulating film minimizes inter-electrode capacitance, thus improving figure of merit without compromising voltage handling.
Solution Approach 2:
The first insulating film acts as an intermediary layer that provides electrical isolation and withstand voltage capability, while the second insulating film serves as another intermediary that specifically reduces capacitance between the gate and field plate electrodes. These intermediary layers resolve the contradiction between voltage strength and capacitance reduction.
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 decreases the input capacitance, thereby reducing the product of on-resistance and input capacitance, enhancing the figure of merit and allowing for higher withstand voltage while minimizing heat generation and thermal breakdown risks.
Implementation Method 1
using a second insulating film to reduce the inter-electrode capacitance by thermally oxidizing the upper portion of the field plate electrode
Data Source
AI summary
According to one embodiment, in a semiconductor device, a first semiconductor layer of a first conductivity type has a first impurity concentration. A second semiconductor layer of the first conductivity type is formed on the first semiconductor layer and has a second impurity concentration lower than the first impurity concentration. A field plate electrode is formed in a lower portion of a trench formed in the second semiconductor layer through a first insulating film so as to bury the lower portion of the trench. A second insulating film is formed in the upper portion of the trench so as to be in contact with the top surface of the field plate electrode. A gate electrode is formed in the upper portion of the trench through a gate insulating film so as to bury the upper portion of the trench to sandwich the second insulating film.