TMBS Diode Floating P-Well for Low Forward Voltage and Robustness
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Solution Overview
Problem
Current Schottky diodes are not suitable for motor vehicle generator systems due to high forward voltage, high reverse current, and poor robustness, especially at high temperatures, which leads to inefficiency and potential thermal instability.
Innovation Solution
A Trench MOS Barrier Schottky diode (TMBS) with floating p-wells under the trench bottom is designed, where the PN diode acts as a clamp element, reducing the electric field strength in the oxide layer and providing an angular blocking characteristic, thus integrating robustness and lower forward voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Schottky diodes are used to reduce forward voltage, then forward voltage is reduced, but reverse current increases and robustness deteriorates
Solution Approach 1:
The device is segmented into multiple functional regions: a planar Schottky contact region for low forward voltage, a trench MOS structure for reverse current suppression, and a floating p-well for robustness enhancement. Each segment performs a specific function, and their combination resolves the contradiction between low forward voltage and high robustness.
Solution Approach 2:
The device combines different material structures and physical principles: Schottky metal-semiconductor contact, silicon oxide insulator layer, and PN junction in the floating p-well. This composite structure integrates the advantages of each component to achieve low forward voltage, low reverse current, and high robustness simultaneously.
2Use of energy by moving object
If Schottky diodes are used to reduce forward voltage, then forward voltage is reduced, but reverse current increases especially at high temperatures
Solution Approach 1:
The device separates the current conduction path into two distinct regions: the Schottky contact region for forward conduction and the trench MOS structure with floating p-well for reverse blocking. This segmentation allows each region to be optimized for its specific function, reducing reverse current while maintaining low forward voltage.
Solution Approach 2:
The floating p-well acts as an intermediary element between the Schottky contact and the substrate. It forms a PN junction that provides an additional reverse blocking barrier, preventing thermally generated carriers from causing high reverse current at elevated temperatures while not affecting the Schottky contact's low forward voltage characteristic.
3Use of energy by moving object
If conventional Schottky diodes are used, then forward voltage is reduced, but thermal instability occurs due to positive electrical-thermal feedback
Solution Approach 1:
The floating p-well is pre-configured to provide reverse blocking action before thermal runaway can occur. The PN junction in the floating p-well creates a potential barrier that limits reverse current flow at elevated temperatures, preventing the positive electrical-thermal feedback loop that leads to thermal instability.
Solution Approach 2:
The floating p-well structure provides negative feedback by limiting reverse current flow when temperature increases. As temperature rises and reverse current tends to increase, the PN junction in the floating p-well becomes more effective at blocking carriers, reducing the reverse current and preventing thermal runaway.
4Object-generated harmful factors
If the effective area for current flow is reduced in TMBS, then reverse currents are reduced, but forward voltage increases
Solution Approach 1:
The device segments the current flow paths: forward current flows through the low-resistance Schottky contact region with large effective area, while reverse current is blocked by the trench MOS structure and floating p-well. This segmentation allows the forward conduction area to be large (low forward voltage) while the reverse blocking structure limits reverse current.
Solution Approach 2:
Different regions of the device have different local properties optimized for their specific functions: the Schottky contact region has high conductivity for forward current, the trench region has insulating oxide for reverse blocking, and the floating p-well has PN junction properties for additional reverse current suppression. This local quality optimization resolves the contradiction between forward voltage and reverse 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 TMBS with floating p-wells offers high robustness and stability, reducing reverse currents and power loss, making it suitable for use as a Z diode in motor vehicle generator systems by managing electric field strength and preventing thermal instability.
Implementation Method 1
The PN diode composed of the floating p-wells and the n-epi layer determines the breakdown voltage of the TMBS and functions as a clamp element
Implementation Method 2
oxide layers between the ditches and the metal layer
Implementation Method 3
Schottky diode with a Schottky barrier between the metal layer as anode and the n-epi layer as cathode
Implementation Method 4
In the blocking direction, space charge zones form both in the MOS structure and in the Schottky diode. The space charge zones expand with increasing voltage and collide in the middle of the region between the adjacent trenches together. This shields the Schottky effects responsible for high reverse currents
Data Source
Figure 1~2
Figure 3
AI summary
Proposed is a semiconductor arrangement comprising a trench MOS barrier Schottky diode (TMBS) consisting of an n-type epitaxial layer (2), in which are situated in a two-dimensional manner of presentation at least two trenches (6) introduced by etching, on an n+-type substrate (1), which serves as a cathode zone. An electrically floating p-doped layer, which serves as an anode zone of the PN diode, is situated in the n-doped epitaxial layer (2) at least at a location below the trench bottom. An oxide layer lies between a metal layer (4) and the surface of the trenches (6). The n-doped epitaxial layer (2) can also be composed of two n-type layers doped with different doping levels.