U-Shaped Polysilicon Resistor for Compact IC Layout
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Solution Overview
Problem
Conventional polysilicon resistors in integrated circuits occupy valuable area and hinder access to other components due to their horizontal extension, requiring complex connections and additional components, and existing trench resistors are complicated to form and connect.
Innovation Solution
A serpentine polysilicon resistor design with continuous U-shape and lateral bottom, integrated into a semiconductor-on-insulator substrate with a buried insulator layer and a dopant-including high resistivity polycrystalline layer, allowing for customized resistivity and improved thermal dissipation without the need for specific trench formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional polysilicon resistors are formed horizontally in ILD layers, then they provide scaling interconnects for the IC, but they occupy valuable area and block access to other functional components therebelow
Solution Approach 1:
The patent transitions the resistor structure from a horizontal planar configuration to a vertical three-dimensional configuration by forming the polysilicon resistor element within a trench that extends into the substrate. This vertical orientation reduces the horizontal footprint of the resistor while maintaining its electrical function, thereby freeing up valuable planar area and eliminating blocking of underlying components.
Solution Approach 2:
The resistor structure is nested within the trench formation process that is already part of the bipolar fabrication sequence. The polysilicon resistor element is formed within the trench, utilizing the same vertical space that would otherwise be empty or filled with isolation material, thereby efficiently using the available three-dimensional space without adding extra process steps.
2Area of stationary object
If trench resistors are used to minimize area, then the horizontal footprint is reduced, but the formation process becomes complicated requiring specific trench formation, filling, and connection steps
Solution Approach 1:
The patent merges the resistor formation process with the existing trench isolation and bipolar device fabrication steps. The same trench that is formed for isolation purposes is also used to house the polysilicon resistor element, eliminating the need for separate trench formation, filling, and connection steps that would otherwise be required for traditional trench resistors.
Solution Approach 2:
The trench structure serves multiple functions: it provides isolation for bipolar devices and simultaneously houses the polysilicon resistor element. This multi-functional use of the trench structure simplifies the overall fabrication process by eliminating the need for dedicated resistor trenches and associated connection steps.
3Temperature
If resistors are formed over oxide or STI to reduce thermal dissipation into substrate, then thermal isolation is improved, but the resistors extend horizontally taking up valuable area
Solution Approach 1:
The patent resolves this contradiction by changing the resistor geometry from horizontal to vertical. The polysilicon resistor element is formed within a trench that extends into the substrate, providing thermal isolation from the substrate while minimizing horizontal footprint. The vertical configuration allows thermal dissipation control without sacrificing planar area.
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 design provides an ultra-compact, programmable resistor with enhanced heat dissipation and reduced horizontal surface area, offering improved electrical isolation and thermal conductivity while simplifying the fabrication process.
Implementation Method 1
dopant-including high resistivity (HR) polycrystalline layer below the buried insulator layer and below each polysilicon resistor element in the base semiconductor substrate
Implementation Method 2
an insulator within a valley of the continuous U-shape of each polysilicon resistor element
Data Source
AI summary
A resistor includes at least one polysilicon resistor element in a semiconductor substrate with each polysilicon resistor element having a continuous U-shape with a continuous lateral bottom. The resistor may include an insulator within a valley of the U-shape of each polysilicon resistor element. A plurality of polysilicon resistor elements can be sequentially interconnected to create a serpentine polysilicon resistor. The resistor may also include a dopant-including high resistivity (HR) polysilicon layer thereunder to provide electrical isolation from, and better thermal conduction to, for example, a base semiconductor substrate. The resistor can be used in an SOI substrate. A related method is also disclosed.