Super Junction FET Floating Ring for Breakdown Voltage
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Solution Overview
Problem
Conventional Super Junction field effect transistor fabrication processes face challenges in maintaining charge balance between P− type and N− type dopants, leading to breakdown voltage inconsistencies due to process variations, especially at edges and corners, and are costly due to complex process steps.
Innovation Solution
Incorporating a floating ring-shaped P− type epitaxial semiconductor column within the charge compensation region, electrically isolated from the source metal terminal, which reduces electric field and mitigates process variation effects, enhancing avalanche breakdown voltage and device ruggedness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tight process control is implemented to maintain charge balance between P− type and N− type dopants, then breakdown voltage requirement is satisfied, but manufacturing complexity and cost increase
Solution Approach 1:
An intermediate P− type column is introduced between the N− type region and the source metal terminal. This intermediate structure acts as a mediator that gradually transitions the electric field, preventing sudden field concentration at the interface. The intermediate P− type column with its specific doping concentration (between 1×10^16 and 1×10^18 atoms/cm³) serves as a buffer zone that smooths the charge distribution, thereby maintaining breakdown voltage consistency without requiring extremely tight process control on the main P− type and N− type dopant concentrations.
2Reliability
If conventional super junction fabrication processes are used to form P− type columns, then charge compensation is achieved, but manufacturing cost increases due to many delicate process steps
Solution Approach 1:
The charge compensation region is segmented into multiple distinct P− type columns with different doping concentrations arranged in a specific sequence. The first P− type column has a first doping concentration, the intermediate P− type column has a second doping concentration (between 1×10^16 and 1×10^18 atoms/cm³), and the second P− type column has a third doping concentration. This segmentation allows each column to perform a specific function in the electric field distribution, achieving better charge balance with more robust fabrication processes.
Solution Approach 2:
Different regions of the charge compensation structure are assigned different doping concentrations tailored to their specific functional requirements. The intermediate P− type column positioned near the source metal terminal uses a moderate doping concentration (1×10^16 to 1×10^18 atoms/cm³) to create a gradual electric field transition, while other P− type columns use higher concentrations for strong charge compensation. This local optimization of doping quality enables effective charge balance without requiring uniformly tight process control throughout the entire structure.
3Ease of manufacture
If P− type and N− type dopant concentrations are imbalanced due to process variation, then breakdown voltage requirement is not satisfied, but process control is simplified
Solution Approach 1:
The intermediate P− type column is designed as a pre-configured buffer structure that anticipates and compensates for potential dopant concentration imbalances. By positioning this column with a specifically engineered doping concentration (between 1×10^16 and 1×10^18 atoms/cm³) between the source metal terminal and the main charge compensation region, the structure creates a cushioning effect that absorbs variations in dopant concentrations. This beforehand cushioning ensures that even if process variations cause imbalances in the main P− type and N− type dopants, the breakdown voltage requirement remains satisfied.
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 floating ring-shaped P− type column increases avalanche breakdown voltage by at least 0.2% and makes the device less susceptible to process variations, resulting in a more rugged and consistently performing Super Junction FET with improved breakdown voltage characteristics.
Implementation Method 1
An oxide layer is disposed above an upper surface of the floating ring-shaped P− type column. The oxide layer is disposed between the upper surface of the floating ring-shaped P− type column and the source metal terminal of the Super Junction FET device. Accordingly, the floating ring-shaped P− type column is not electrically coupled to the source metal terminal and the floating ring-shaped P− type column is electrically isolated from the source metal terminal.
Implementation Method 2
During blocking mode operation, the upper surface of the floating ring-shaped P− type column will exhibit a positive voltage greater than zero. This is due in part to capacitive coupling effects between the floating ring-shaped P− type column and the adjacent P− type columns. The electric field is lower along the floating ring-shaped P− type column than the electric field along the other P− type columns that are electrically coupled to the source metal terminal.
Implementation Method 3
This is due in part to capacitive coupling effects between the floating ring-shaped P− type column and the adjacent P− type columns.
Implementation Method 4
The charge compensation region includes a first plurality of columns of P− type epitaxial semiconductor material within a region of N− type epitaxial semiconductor material, a floating ring-shaped column of P− type epitaxial semiconductor material within the region of N− type epitaxial semiconductor material, and a second plurality of columns of P− type epitaxial semiconductor material within the region of N− type epitaxial semiconductor material. The alternating P− type and N− type semiconductor material forms the charge compensation region.
Data Source
AI summary
A Super Junction Field Effect Transistor (FET) device includes a charge compensation region disposed on a substrate of semiconductor material. The charge compensation region includes a set of strip-shaped P− type columns, a floating ring-shaped P− type column that surrounds the set of strip-shaped P− type columns, and a set of ring-shaped P− type columns that surrounds the floating ring-shaped P− type column. A source metal is disposed above portions of the charge compensation region. The source metal contacts each of the strip-shaped P− type columns and each of the ring-shaped P− type columns. An oxide is disposed between the floating P− type column and the source metal such that the floating P− type column is electrically isolated from the source metal. The device exhibits a breakdown voltage that is 0.2% greater than if the floating P− type column were to contact the source metal.