Fin-Based LDMOS Structure for Low Rsp and High Breakdown Voltage
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Solution Overview
Problem
LDMOS transistors face a trade-off between on-resistance (Rsp), breakdown voltage (BDV), and safe operating area (SOA), where reducing Rsp often results in lower BDV, and increasing BDV can lead to higher Rsp and compromised SOA.
Innovation Solution
The development of a fin-based LDMOS transistor structure, which includes forming fins in a rectilinear or circle and spoke pattern on a semiconductor substrate, diffusing implants into the substrate and fins, and patterning a field plate to control electric potential distribution and reduce local electric field increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the doping concentration in the drain region is increased to reduce on-resistance, then on-resistance decreases, but breakdown voltage decreases
Solution Approach 1:
The patent applies local quality by creating laterally-diffused doped regions with specific doping concentrations that are localized in the drain and channel regions. The p-type channel region is diffused laterally from the drain region, creating a graded doping profile that optimizes both on-resistance and breakdown voltage locally in different areas of the device structure.
Solution Approach 2:
The patent transitions from a planar doping structure to a three-dimensional laterally-diffused structure. The p-type dopants are diffused laterally from the drain region into the channel region, creating a depth-wise and lateral concentration gradient that simultaneously affects both on-resistance and breakdown voltage through a multi-dimensional doping profile.
2Strength
If the depletion layer width is increased to increase breakdown voltage, then breakdown voltage increases, but on-resistance increases
Solution Approach 1:
The patent creates a localized p-type channel region that is laterally diffused from the drain region. This localized doping creates a narrow depletion layer in the channel region where needed for low on-resistance, while maintaining a wider depletion layer in the drain region for high breakdown voltage, thus resolving the contradiction through spatially differentiated doping.
Solution Approach 2:
The laterally-diffused doping structure creates a three-dimensional doping profile that enables independent control of depletion layer width in different spatial regions. The lateral diffusion from the drain region creates a doping gradient that simultaneously achieves narrow depletion width (low on-resistance) in the channel and wide depletion width (high breakdown voltage) in the drain.
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 simultaneously improves both on-resistance (Rsp) and breakdown voltage (BDV) while maintaining a robust safe operating area (SOA), effectively addressing the trade-offs inherent in traditional LDMOS transistor designs.
Implementation Method 1
diffusing first and second implants into the semiconductor substrate and first and second fins
Data Source
AI summary
In some implementations, a method includes forming first and second fins on a semiconductor substrate. The method further includes diffusing first and second implants into the semiconductor substrate and first and second fins. The method also includes patterning a field plate on the semiconductor substrate. An active device, such as a laterally-diffused metal-oxide semiconductor field effect (LDMOS) transistor can be formed in this way.