Diffusion Resistor Voltage Coefficient Reduction via CMOS Well Segmentation
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Solution Overview
Problem
Conventional diffusion resistors in integrated circuits have low breakdown voltage and high voltage coefficient of resistivity, making them unsuitable for high voltage applications, and existing alternatives like polysilicon resistors are prone to process variations and higher manufacturing costs.
Innovation Solution
The design involves spacing the body region of the resistor well away from the outlying well structure by using a pwell implant mask to create a lightly doped well-free region, where most of the potential drop occurs, reducing depletion within the resistor well and increasing breakdown voltage while maintaining low voltage coefficient of resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional nwell diffusion resistors are used, then the resistor structure is compact and easy to manufacture, but the breakdown voltage is low and voltage coefficient of resistivity is high
Solution Approach 1:
The patent segments the well structure into two distinct parts: a heavily doped nwell resistor body and a lightly doped surrounding well region. This segmentation allows the resistor to maintain compact dimensions while the lightly doped region extends the depletion region into the substrate, thereby increasing breakdown voltage without compromising manufacturability
Solution Approach 2:
The patent applies local quality by creating different doping concentrations in different regions of the well structure. The central resistor body maintains heavy doping for low resistance and compact size, while the surrounding well region uses light doping to extend the depletion region and increase breakdown voltage, thus optimizing both manufacturability and reliability in different locations
2Area of stationary object
If conventional nwell diffusion resistors are used, then the resistor structure is compact, but the voltage coefficient of resistivity is high due to lateral extension of depletion region
Solution Approach 1:
The patent segments the well structure into a heavily doped central nwell resistor body and a lightly doped surrounding well region. This segmentation confines the depletion region extension to the lightly doped surrounding area, preventing lateral depletion into the heavily doped resistor body, thereby maintaining a compact resistor area while reducing the voltage coefficient of resistivity
Solution Approach 2:
The patent applies local quality by creating a lightly doped surrounding well region that specifically addresses the voltage coefficient problem. This localized change in doping concentration allows the depletion region to extend laterally without affecting the heavily doped resistor body, thus reducing VCR while maintaining compact dimensions
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 enhances the breakdown voltage and reduces the voltage coefficient of resistivity, making the diffusion resistors more suitable for high voltage applications while maintaining size and current carrying capabilities comparable to polysilicon resistor solutions.
Implementation Method 1
The first well is formed by a plurality of successively deeper implantations, with a deepest implantation defining a first range as deep or deeper than an isolation structure depth. A second well is formed by a plurality of successively deeper implantations of another conductivity type.
Implementation Method 2
Diffusion resistors or well resistors are commonly implemented as nwell structures in P− substrate twin-well bulk CMOS technology
Data Source
AI summary
Integrated circuits and manufacturing methods are presented for creating diffusion resistors (101, 103) in which the diffusion resistor well is spaced from oppositely doped wells to mitigate diffusion resistor well depletion under high biasing so as to provide reduced voltage coefficient of resistivity and increased breakdown voltage for high-voltage applications.