LDMOS Transistor Doped Implant Reduces Leakage on High-Resistivity Substrate
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Solution Overview
Problem
Active semiconductor devices, such as LDMOS transistors, on high-resistivity substrates experience unacceptably high drain current leakage and low breakdown voltage, which are critical issues in RF power amplifiers where low loss and high performance are essential.
Innovation Solution
A relatively deep doped implant region is formed in the high-resistivity substrate surrounding the active area of the LDMOS transistor and underlying a field oxide region, effectively reducing drain current leakage and increasing breakdown voltage by using a doped implant region with a doping concentration at least an order of magnitude greater than the substrate, connected to the device ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If high-resistivity substrate is used, then substrate RF power loss is reduced, but drain current leakage increases and breakdown voltage decreases
Solution Approach 1:
The patent applies local quality by creating a doped implant region with specific doping concentration (at least an order of magnitude greater than the substrate) in a localized area surrounding the active device area and underlying the field oxide region. This localized doped region modifies the electrical properties only where needed, reducing drain current leakage and increasing breakdown voltage without affecting the overall high-resistivity substrate benefits for RF power loss reduction.
Solution Approach 2:
The patent changes the doping concentration parameter in a specific region of the substrate. By introducing a doped implant region with doping concentration at least an order of magnitude greater than the high-resistivity substrate, the electrical characteristics (drain current leakage and breakdown voltage) are improved while maintaining the high-resistivity substrate's low RF power loss property in other regions.
2Loss of energy
If high-resistivity substrate is used, then low loss performance is achieved, but device layout performance deteriorates
Solution Approach 1:
The patent introduces a localized doped implant region surrounding the active device area to improve device layout performance. This local modification addresses the performance deterioration in specific areas without compromising the overall low loss performance achieved by the high-resistivity substrate, thereby resolving the contradiction between low loss and device layout performance.
3Reliability
If doped implant region is added, then drain current leakage is reduced and breakdown voltage is increased, but device complexity increases
Solution Approach 1:
The doped implant region acts as an intermediary element between the high-resistivity substrate and the active device. It mediates the electrical characteristics by providing a transition zone with higher doping concentration that reduces drain current leakage and increases breakdown voltage, while the field oxide region provides physical isolation. This intermediary structure resolves the reliability issues without requiring complete redesign of the entire device.
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 doped implant region significantly reduces drain current leakage and increases breakdown voltage to levels comparable to conventional silicon substrates, enhancing the performance of LDMOS transistors on high-resistivity substrates while maintaining the benefits of low loss and high performance.
Implementation Method 1
a doped implant region formed in the substrate surrounding the active area of the active semiconductor device... with a doping concentration at least an order of magnitude greater than a doping concentration of the substrate
Implementation Method 2
The doped implant region may effectively reduce the drain current leakage and increase the breakdown voltage
Data Source
AI summary
An active semiconductor device, such as a laterally diffused metal oxide semiconductor (LDMOS) transistor, includes a substrate having a substrate resistivity of at least 1 kohm-cm. An active area of the active semiconductor device is formed in the substrate. A doped implant region is formed in the substrate surrounding the active area of the active semiconductor device and a field oxide region is formed over the doped implant region. The doped implant region may include a boron dopant. Methodology entails forming the doped implant region prior to formation of the field oxide region.