RF-LDMOS Transistor Source-Isolation Drain Structure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
RF-LDMOS transistors available within a given RF-LDMOS diffusion technology are not suitable for use in a DC biasing circuit due to their source being typically connected to the substrate, preventing source-high operation which is necessary for efficient DC biasing in power amplifiers.
Innovation Solution
A power amplifier design that includes an RF-LDMOS transistor with a drain region extending beneath the gate, source region, and a p-type body region, allowing the source to be isolated from the substrate and operated at a higher voltage, utilizing a silicide layer for common connection and ion implantation to form epitaxial doped regions, enhancing reduced surface field (RESURF) action and breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the source region is connected to the substrate (conventional design), then the device structure is simple and manufacturing is easier, but the device cannot operate in source-high mode which is necessary for efficient DC biasing
Solution Approach 1:
The device structure is segmented by introducing a drain region that extends beneath the source region and body region, electrically isolating the source from the substrate. This segmentation allows the source to be operated at a higher potential than the substrate, enabling source-high operation mode while maintaining structural integrity.
Solution Approach 2:
The drain region extends in the vertical dimension beneath the gate, source region, and body region, creating a three-dimensional isolation structure. This dimensional extension allows electrical isolation of the source from the substrate without complicating the planar surface layout, resolving the contradiction between adaptability and structural complexity.
2Reliability
If the drain region extends deeply beneath the substrate to isolate the source, then source isolation is improved, but the manufacturing precision and field distribution may be compromised
Solution Approach 1:
The drain region is designed with non-uniform depth characteristics - it extends deeply beneath the source and body regions to provide isolation, while its depth beneath the gate is controlled to be shallower. This local variation in depth optimizes both isolation reliability and field distribution, preventing excessive field concentration that would occur with uniform deep extension.
Solution Approach 2:
The drain region's depth parameter is varied spatially - deeper beneath the source/body regions for isolation and shallower beneath the gate for field control. This parameter change approach allows simultaneous optimization of source isolation reliability and field distribution uniformity, resolving the contradiction between these two requirements.
3Ease of manufacture
If the drain region is formed by ion implantation and diffusion, then the manufacturing process is established, but the surface field distribution may be unfavorable for high breakdown voltage
Solution Approach 1:
The drain region exhibits local quality variations in depth - shallower beneath the gate and deeper beneath the source and body regions. This local depth differentiation improves surface field distribution and reduces peak field intensity at the surface, thereby enhancing breakdown voltage while maintaining compatibility with ion implantation and diffusion manufacturing processes.
Solution Approach 2:
The shadowing effect during ion implantation, which would normally be considered a manufacturing limitation, is converted into a beneficial feature. The gate structure's shadowing naturally creates the desired shallower drain region beneath the gate, transforming a potential manufacturing defect into a field-distribution-optimizing feature that enhances breakdown voltage.
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
Enables the operation of the power amplifier as a source-high device, suitable for use in DC biasing circuits, improving field distribution and achieving higher maximum drain-to-source voltage due to enhanced RESURF action, thus compensating for temperature and manufacturing variations.
Implementation Method 1
The drain region having the first conductivity type extending beneath the region having the second conductivity type allows the source region of the device to be isolated from the underlying region of the substrate whereby, during use, different voltages may be applied to the source and the substrate
Implementation Method 2
such a method may include implanting ions through the major surface of the substrate for forming the drain region and then heating the substrate to diffuse the implanted ions to form the drain region
Implementation Method 3
heating the substrate to diffuse the implanted ions to form the drain region
Implementation Method 4
The relative shallowness of the part of the drain region located beneath the gate may be formed by shadowing of this part of the device by the gate during ion implantation
Implementation Method 5
The relative shallowness of the part of the drain region located beneath the gate may improve the field distribution within the device, allowing for a higher maximum drain to source voltage BV dss owing to the reduced surface field (RESURF) action in the device
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A semiconductor device and a method of making the same. The device includes a semiconductor substrate having a major surface. the device also includes a gate located on the major surface. The device further includes a drain region having a first conductivity type. The device also includes a source region having the first conductivity type, wherein the source region is located within a region having a second conductivity type. The device further includes a channel region comprised of a part of the region having the second conductivity type that is located beneath the gate. The drain region extends laterally away from the gate along the major surface of the substrate. The drain also extends beneath the gate, the source region and the region having the second conductivity type to isolate the source region and the region having the second conductivity type from an underlying region of the substrate.