N-well Capacitor Floating Region Reduces Capacitance Variation
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Solution Overview
Problem
Existing semiconductor capacitors exhibit significant capacitance variation with applied voltage, making them unsuitable for applications requiring constant capacitance across a range of voltages, especially in RF components and systems with alternate polarity operation.
Innovation Solution
A capacitive structure is designed with a stack of doped semiconductor regions, including a floating semiconductor region to isolate the capacitor channel from the substrate, allowing for reduced capacitance variation by shifting the working point and preventing direct biasing of the PN junction, thereby maintaining stable capacitance across varying voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional NMOS capacitor structure is used, then the capacitor can be integrated into the semiconductor device with standard CMOS processes, but the capacitance varies significantly with applied voltage, making it unsuitable for RF applications and alternate polarity operation
Solution Approach 1:
The semiconductor substrate is divided into multiple doped regions with different conductivity types (first doped region, second doped region, third doped region) to create a segmented structure that isolates the capacitor channel from the substrate. This segmentation allows the capacitor to maintain stable capacitance across voltage ranges and enables alternate polarity operation by preventing direct biasing of the PN junction at the substrate interface.
2Productivity
If deep trench capacitors are used to increase bit density, then storage capacity is improved, but additional complex process steps are required for forming deep trenches and filling with conductive and dielectric materials
Solution Approach 1:
The capacitive structure utilizes the same doped semiconductor regions and fabrication processes already required for forming transistors in CMOS devices. The first, second, and third doped regions serve dual purposes: they form the capacitor structure while also being compatible with standard transistor fabrication, eliminating the need for separate deep trench formation and filling processes.
3Device complexity
If the capacitor channel is directly connected to the substrate, then the structure is simplified, but leakage is increased and capacitance control is compromised
Solution Approach 1:
The second doped semiconductor region with conductivity type inverse to the first and third doped regions acts as an intermediary layer between the capacitor channel and the substrate. This intermediate region prevents direct connection, thereby reducing leakage current while maintaining structural integrity and enabling better capacitance control without requiring overly complex isolation structures.
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 capacitive structure achieves reduced capacitance variation over a specified voltage range, enabling efficient operation with alternate polarity and minimizing leakage, thus addressing the limitations of conventional capacitors.
Implementation Method 1
a dielectric region formed on a portion of the first doped semiconductor region
Implementation Method 2
a third doped semiconductor region positioned, in a depth direction, between the first and second doped semiconductor regions so as to delineate the first doped semiconductor region in the depth direction, wherein the third doped semiconductor region has a second conductivity type that is inverse to the first conductivity type
Data Source
AI summary
A capacitor, such as an N-well capacitor, in a semiconductor device includes a floating semiconductor region, which allows a negative biasing of the channel region of the capacitor while suppressing leakage into the depth of the substrate. In this manner, N-well-based capacitors may be provided in the device level and may have a substantially flat capacitance/voltage characteristic over a moderately wide range of voltages. Consequently, alternating polarity capacitors formed in the metallization system may be replaced by semiconductor-based N-well capacitors.