Semiconductor Device With Trench Schottky Junction
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Solution Overview
Problem
Power MOSFETs with a field plate structure face increased on-resistance and leakage current due to longer lateral periods, which enhance electric field strength at the Schottky junction, making it difficult to achieve both low on-resistance and high breakdown voltage.
Innovation Solution
A semiconductor device with a vertical electrode structure incorporating an embedded field plate structure and a Schottky barrier diode, where the Schottky junction is formed at the sidewall of a trench, reducing electric field strength and allowing for a shorter lateral period without increasing on-resistance, and including a guard ring layer to moderate the electric field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the lateral period of the field plate structure is increased to form a Schottky barrier diode, then the Schottky junction area is increased, but the on-resistance is raised and leakage current is increased
Solution Approach 1:
The patent transitions from forming the Schottky junction in the planar direction (lateral period extension) to forming it vertically at the sidewall of the trench. This dimensional change allows the Schottky junction area to be increased without increasing the lateral cell pitch, thereby avoiding the increase in on-resistance and leakage current that would result from lateral expansion.
Solution Approach 2:
The Schottky junction is formed within the trench structure by having the Schottky barrier diode electrode contact the drift layer at the trench sidewall. This nested configuration integrates the Schottky diode formation within the existing trench geometry, maximizing space utilization without increasing the lateral footprint.
2Adaptability or versatility
If the lateral period is extended to accommodate Schottky junction formation, then the cell unit size is increased, but the on-resistance increases due to longer depletion layer extension distance
Solution Approach 1:
The invention moves the Schottky junction formation from the lateral dimension to the vertical dimension by utilizing the trench sidewall. This allows the Schottky barrier diode to be integrated into the existing cell structure without extending the lateral period, thereby maintaining low on-resistance while achieving diode functionality.
3Area of moving object
If the lateral period is increased to form Schottky junction, then more space is available for diode formation, but the electric field strength at the Schottky junction is enhanced causing increased leakage current
Solution Approach 1:
By forming the Schottky junction at the vertical sidewall of the trench rather than in the lateral direction, the patent achieves sufficient Schottky junction area without increasing the lateral period. This dimensional transition prevents the enhancement of electric field strength that would occur with lateral expansion, thereby reducing leakage current.
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 solution effectively reduces on-resistance and leakage current while maintaining high breakdown voltage, enabling efficient operation of the power MOSFET with a Schottky barrier diode by moderating the electric field strength and allowing for a larger Schottky junction area without increasing the cell pitch.
Implementation Method 1
A Schottky junction formed of the second main electrode and the first semiconductor layer is formed at a sidewall of the second trench
Implementation Method 2
a depletion layer is extended from the field plate structure in a lateral direction of the drift layer when a voltage is applied. Thereby, a high breakdown voltage is maintained.
Data Source
AI summary
A semiconductor device includes a first semiconductor layer of a first conductivity type. A second semiconductor layer of a second conductivity type is on the first semiconductor layer. A third semiconductor layer is on the second semiconductor layer. A fourth semiconductor layer is selectively in the first semiconductor layer. A first trench and second trench penetrate from a surface of the third layer through the second layer to reach the first layer. An embedded electrode is in the first trench. A control electrode is above the embedded electrode via an insulating film. A lower end of the second trench is connected to the fourth semiconductor layer. A first main electrode is electrically connected to the first layer. A second main electrode is provided in the second trench. A Schottky junction is formed by the first layer and the second main electrode at a sidewall of the second trench.