Shielded MOM Capacitor Structure for Stable Capacitance
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Solution Overview
Problem
MOM capacitors experience fluctuations in capacitance value due to voltage application, primarily caused by the expansion and contraction of the depletion layer in the semiconductor substrate, which existing techniques fail to effectively suppress.
Innovation Solution
A capacitive element is designed with a shielding layer between the semiconductor substrate and the capacitor structure, sharing the same potential as the substrate, to reduce the influence of the electric field and stabilize the depletion layer, thereby minimizing parasitic capacitance fluctuations. The shielding layer is formed to surround the capacitor structure and is composed of a conductive polysilicon layer on a thermal oxide film, with a well region of opposite conductivity type to further stabilize the potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a MOM capacitor structure is used to increase capacitance density, then the capacitance density is improved, but fluctuations in capacitance value due to voltage application occur
Solution Approach 1:
A shielding layer is introduced as an intermediary component between the capacitor structure and the semiconductor substrate. This shielding layer, formed of conductive material and connected to a fixed potential, mediates the electric field interaction by providing a stable reference potential that prevents direct coupling between the capacitor electrodes and the substrate, thereby suppressing capacitance fluctuations while preserving the high capacitance density of the MOM structure
Solution Approach 2:
The shielding layer is maintained at a constant potential (equipotential surface) through connection to a fixed voltage node. This equipotential condition creates a stable electric field environment that prevents potential fluctuations from propagating to the capacitor structure, thereby stabilizing the capacitance value while allowing the MOM structure to maintain its high capacitance density
2Reliability
If a shield electrode is added around the capacitor structure to suppress electrostatic coupling, then parasitic capacitance is reduced, but device complexity increases
Solution Approach 1:
The shielding function is merged with the existing substrate structure by forming the shielding layer directly on the semiconductor substrate. This integration approach combines the substrate's mechanical support function with the new electrostatic shielding function, achieving parasitic capacitance suppression without adding separate shield electrode structures and thereby avoiding increased device complexity
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 configuration effectively suppresses fluctuations in capacitance value by shielding the semiconductor substrate from the electric field, resulting in stable capacitance over time, even after voltage application, enhancing the accuracy of semiconductor devices like A/D converters.
Implementation Method 1
a shielding layer formed between the semiconductor substrate and the capacitor structure... the shielding layer is formed to overlap with the capacitor structure so as to surround a periphery of the capacitor structure
Implementation Method 2
the capacitor structure generates main capacitance by electrostatic coupling in an electric field in an in-plane direction
Implementation Method 3
a thermal oxide film is formed on the semiconductor substrate, and the shielding layer is a conductive polysilicon layer formed on the thermal oxide film
Data Source
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AI summary
The present invention provides a capacitive element which is capable of suppressing fluctuations in capacitance value due to application of a voltage. A capacitive element (100) includes a P-type semiconductor substrate (110), a capacitor structure (150) formed above the P-type semiconductor substrate (110), and a shielding layer (130) formed between the P-type semiconductor substrate (110) and the capacitor structure (150) and electrically connected to the P-type semiconductor substrate (110). Preferably, a pair of electrodes (150a and 150b) in the capacitor structure (150) are at a first potential (V1) and a second potential (V2) respectively, and the P-type semiconductor substrate (110) and the shielding layer (130) are at a third potential (V3).