RF LDMOS Device Well Structure Snapback Threshold
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Solution Overview
Problem
RF LDMOS devices in high-power RF applications face reliability issues due to premature breakdown caused by the snapback effect, which is triggered by a low drain voltage threshold, and existing methods to increase this threshold are limited by non-adjustable breakdown voltage and high channel resistance.
Innovation Solution
The introduction of a first and second well with a specific conductivity type in the substrate under the channel and drain regions, respectively, formed through an ion implantation process, reduces channel resistance and enhances breakdown resistance, ensuring most drain current flows towards the substrate, thereby increasing the snapback effect triggering drain voltage threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the breakdown voltage between drain region and substrate is increased by adjusting dopant concentrations, then the snapback threshold can be raised, but the dopant concentrations are predetermined and not adjustable for a given design
Solution Approach 1:
The invention divides the substrate into multiple regions with different conductivity types. Specifically, it introduces a first well with first conductivity type and a second well with second conductivity type (opposite to the substrate) at different locations. This segmentation allows independent control of electric field distribution in different regions, enabling adjustment of the snapback threshold without changing the overall substrate dopant concentration.
Solution Approach 2:
The invention applies local quality by creating regions with different doping characteristics within the substrate. The first well and second well have different conductivity types and are positioned at specific locations to locally modify the electric field distribution. This allows the breakdown voltage to be adjusted locally at critical regions (channel and drain areas) while maintaining the predetermined substrate dopant concentration.
2Reliability
If the channel resistance is reduced to increase snapback threshold, then the device performance improves, but the channel resistance reduction is limited by the fixed substrate properties
Solution Approach 1:
The substrate is segmented into multiple functional regions by introducing wells with different conductivity types. The first well is positioned to affect the channel region, while the second well is positioned to affect the drain region. This segmentation enables independent optimization of channel resistance and breakdown characteristics without requiring complete redesign of the substrate structure.
Solution Approach 2:
The invention introduces wells as intermediary structures between the substrate and the active device regions. These wells act as mediators that modify the electric field distribution and carrier concentration in the channel and drain regions, thereby reducing channel resistance and increasing snapback threshold without directly altering the substrate properties.
3Reliability
If the drain voltage threshold for snapback is increased, then device reliability improves, but the breakdown voltage between drain and substrate becomes non-adjustable
Solution Approach 1:
The invention implements local quality by creating specific doped regions (wells) at strategic locations within the substrate. The first well with first conductivity type and the second well with second conductivity type are positioned to locally modify the electric field distribution in the channel and drain regions respectively. This allows the drain voltage threshold to be adjusted locally without changing the overall breakdown voltage characteristics of the drain-substrate junction.
Solution Approach 2:
The invention transitions from controlling breakdown voltage through a single dimension (substrate dopant concentration) to controlling it through multiple dimensions. By introducing wells at different locations with different conductivity types, the electric field distribution can be controlled in multiple spatial dimensions, enabling independent adjustment of the snapback threshold while maintaining the predetermined substrate properties.
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 design effectively raises the drain voltage threshold for snapback, improving the reliability of RF LDMOS devices by reducing channel resistance and enhancing electric field uniformity, while maintaining other device characteristics.
Implementation Method 1
formed through an ion implantation process
Data Source
AI summary
An RF LDMOS device is disclosed, including: a substrate having a first conductivity type; a channel doped region having the first conductivity type and a drift region having a second conductivity type, each in an upper portion of the substrate, the channel doped region having a first end in lateral contact with a first end of the drift region; a first well having the first conductivity type in the substrate, the first well having a top portion in contact with both of a bottom of the first end of the channel doped region and a bottom of the first end of the drift region; and a second well having the first conductivity type in the substrate, the second well having a top portion in contact with a bottom of a second end of the drift region. A method of forming such an RF LDMOS device is also disclosed.