Semiconductor Field-Plate Electrode for Low On-Resistance
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Solution Overview
Problem
In power MOSFETs, there is a trade-off between breakdown voltage and on-resistance due to limitations in impurity concentration and film thickness of the drift layer, which restricts the reduction of on-resistance, and excessive impurity concentration can lead to decreased mobility and increased scattering of carriers.
Innovation Solution
The semiconductor device incorporates a field-plate electrode under the gate electrode, with trenches and alternating trenches to increase channel density and impurity concentration within a predetermined range, optimizing cell pitch and impurity concentration to minimize on-resistance while maintaining high breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If impurity concentration of the drift layer is increased to reduce on-resistance, then on-resistance decreases, but element breakdown voltage decreases
Solution Approach 1:
A field plate electrode is introduced as an intermediary structure between the gate electrode and the drift layer. This field plate electrode, positioned in a trench and separated by an insulating film, mediates the electric field distribution in the drift layer, enabling higher impurity concentration while maintaining breakdown voltage through field cancellation effects from space charges.
Solution Approach 2:
The invention changes the physical parameters of the drift layer by increasing impurity concentration to values of 1×10^17 atoms/cm³ or more, which would normally reduce breakdown voltage. The field plate electrode structure enables this parameter change while compensating for the negative effects through electric field management.
2Productivity
If cell pitch is made fine and impurity concentration is increased to increase channel density, then on-resistance decreases, but carrier mobility decreases due to impurity scattering
Solution Approach 1:
The invention optimizes the cell pitch parameter to 0.6 μm or less and increases impurity concentration to 1×10^17 atoms/cm³ or more, achieving high channel density. The field plate electrode structure compensates for the mobility reduction by managing the electric field environment, allowing these extreme parameter values to be realized.
3Quantity of substance
If impurity concentration of the drift layer is increased beyond a predetermined value, then channel density increases, but on-resistance reduction is limited due to increased carrier scattering
Solution Approach 1:
The field plate electrode acts as an intermediary that modifies the electric field environment in the high-impurity drift layer. By positioning the field plate electrode in a trench with an insulating film, it enables the drift layer to tolerate higher impurity concentrations without excessive carrier scattering, as the field plate structure manages the space charge effects.
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 reduces on-resistance by increasing channel density and optimizing impurity concentration, while maintaining high breakdown voltage and mobility, thus overcoming the limitations of traditional methods.
Implementation Method 1
Since the field plate electrode is provided under the gate electrode, space charges derived from impurities in the drift layer are canceled, allowing electric fields generated in the drift layer to approach a constant value.
Implementation Method 2
The semiconductor device incorporates a field-plate electrode under the gate electrode, with trenches and alternating trenches to increase channel density
Data Source
AI summary
A semiconductor device includes: a drain layer; a drift layer provided on the drain layer; a base region provided on the drift layer; a source region selectively provided on a surface of the base region; a first gate; a field-plate; a second gate; a drain electrode; and a source electrode. The first gate electrode is provided in each of a plurality of first trenches via a first insulating film. The first trenches penetrate from a surface of the source region through the base region and contact the drift layer. The field-plate electrode is provided in the first trench under the first gate electrode via a second insulating film. The second gate electrode is provided in a second trench via a third insulating film. The second trench penetrates from the surface of the source region through the base region and contacts the drift layer between the first trenches.