Lateral MOSFET Drain Segmentation for Rdson and Capacitance
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Solution Overview
Problem
Lateral MOSFETs with substrate drain connections face challenges in achieving optimal transistor characteristics such as gate-to-drain capacitance and Rdson, which are crucial for high-frequency power applications, due to variations in mask alignment and dopant profiles affecting the breakdown voltage and resistance.
Innovation Solution
The design incorporates a heavily doped substrate with epitaxial layers, a diffused tub, active and non-active gate electrodes, and a sinker region, with multiple implantation techniques to create a uniform dopant profile, ensuring precise positioning and consistent transistor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lateral MOSFET designs are used, then manufacturing is simpler, but transistor characteristics such as gate-to-drain capacitance and Rdson are not optimal
Solution Approach 1:
The drain region is segmented into two distinct parts: a lightly doped drain extension region and a heavily doped sinker region. This segmentation allows each region to perform its specific function - the lightly doped region controls gate-to-drain capacitance while the heavily doped sinker reduces Rdson, thereby optimizing transistor characteristics without requiring complete redesign of the entire device
Solution Approach 2:
Different doping concentrations are applied to different spatial locations within the drain region. The drain extension is lightly doped to control capacitance near the gate, while the sinker region is heavily doped to reduce resistance deeper in the substrate. This local quality approach allows simultaneous optimization of electrical characteristics at different locations
2Manufacturing precision
If mask alignment variations occur, then manufacturing is easier, but breakdown voltage and resistance become inconsistent
Solution Approach 1:
The lightly doped drain extension is formed first as a preliminary structure before the heavily doped sinker is created. This preliminary action establishes a defined spatial reference that guides subsequent sinker formation, ensuring consistent relative positioning and predictable electrical characteristics even when absolute mask alignment varies
Solution Approach 2:
The lightly doped drain extension acts as an intermediary structure between the gate and the heavily doped sinker. It provides a controlled transition region that mediates the electrical characteristics, ensuring consistent breakdown voltage and resistance by controlling the electric field distribution regardless of minor alignment variations
3Manufacturing precision
If dopant profiles vary, then manufacturing is simpler, but breakdown voltage and resistance are inconsistent
Solution Approach 1:
The dopant profile is segmented into two distinct concentration regions: a lightly doped drain extension and a heavily doped sinker. This segmentation transforms the complexity of creating a single optimized profile into two simpler, more controllable doping steps, each with less stringent requirements, thereby improving breakdown voltage consistency
Solution Approach 2:
The doping concentration parameter is changed between two distinct regions rather than maintaining a uniform profile. The lightly doped region provides one set of electrical characteristics while the heavily doped sinker provides another, allowing independent optimization of breakdown voltage and resistance through parameter variation across the device structure
4Loss of energy
If Rdson is reduced, then power loss decreases, but gate-to-drain capacitance may increase
Solution Approach 1:
The drain structure is segmented into a lightly doped drain extension region that controls gate-to-drain capacitance and a heavily doped sinker region that reduces Rdson. This segmentation allows the device to achieve low power loss through the heavily doped sinker while maintaining acceptable capacitance through the lightly doped extension
Solution Approach 2:
Different doping qualities are applied locally: light doping near the gate to control capacitance and heavy doping deeper in the substrate to reduce resistance. This local quality approach enables simultaneous optimization of energy loss and capacitance by tailoring the dopant concentration to the specific functional requirements of each spatial region
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 approach enhances the consistency of threshold voltages, reduces Rdson, and maintains acceptable gate-to-drain capacitance, improving the overall performance and reliability of lateral MOSFETs for high-frequency power applications.
Implementation Method 1
multiple implantation techniques to create a uniform dopant profile
Implementation Method 2
diffused tub of a second conductivity type opposite to the first conductivity type formed in the first epitaxial layer
Data Source
AI summary
In one form a lateral MOSFET includes an active gate positioned laterally between a source region and a drain region, the drain region extending from an upper surface of a monocrystalline semiconductor body to a bottom surface of the monocrystalline semiconductor body, and a non-active gate positioned above the drain region. In another form the lateral MOSFET includes a gate positioned laterally between a source region and a drain region, the drain region extending from an upper surface of a monocrystalline semiconductor body to a bottom surface of the monocrystalline semiconductor body, the source region and the drain region being of a first conductivity type, a heavy body region of a second conductivity type in contact with and below the source region, and the drain region comprising a lightly doped drain (LDD) region proximate an edge of the gate and a sinker extending from the upper surface of the monocrystalline body to the bottom surface of the monocrystalline semiconductor body.