Capacitive Sensor Shielding for Parasitic Capacitance Reduction
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Solution Overview
Problem
In capacitance change detection type physical quantity sensors, increased parasitic capacitance between wiring of fixed and movable electrodes deteriorates detection characteristics and reliability due to the proximity of wires, leading to reduced detection accuracy.
Innovation Solution
Incorporating a shield part between the fixed electrode wiring and movable electrode wiring to reduce parasitic capacitance, with the shield part being made of the same material as the movable and fixed electrode parts, and using recessed areas on the substrate to separate and protect the wiring, thereby minimizing parasitic capacitance and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the first wire and second wire are provided closer to each other for downsizing, then the sensor size is reduced, but the parasitic capacitance between the wires increases
Solution Approach 1:
A shield part is introduced as an intermediary component between the first wire and second wire. This shield part acts as a mediator that reduces the parasitic capacitance between the adjacent wires, allowing them to be positioned closer together while maintaining detection accuracy. The shield part is electrically connected to ground potential, creating an equipotential barrier that minimizes capacitive coupling between the signal wires.
Solution Approach 2:
The shield part is electrically connected to ground, creating an equipotential region between the first and second wires. By maintaining the shield part at ground potential, the electric field between the adjacent wires is reduced, thereby minimizing parasitic capacitance. This equipotential approach allows the wires to be positioned closer without compromising measurement accuracy.
2Volume of moving object
If the first wire and second wire are provided closer to each other for downsizing, then the sensor size is reduced, but the detection characteristics are deteriorated
Solution Approach 1:
The shield part serves as a mediator structure positioned between the first and second wires. It reduces the parasitic capacitance that would otherwise interfere with the differential capacitance measurement, enabling accurate detection characteristics even when the wires are closely spaced for miniaturization.
Solution Approach 2:
The shield part is strategically positioned only in the critical region between the first and second wires where parasitic capacitance occurs. This localized approach reduces interference precisely where needed without affecting other parts of the sensor structure, maintaining detection precision while enabling compact wire routing.
3Reliability
If a shield part is provided between the fixed electrode wiring and movable electrode wiring, then the parasitic capacitance is reduced, but the device complexity increases
Solution Approach 1:
The shield part is merged with the substrate structure, and the insulating films are integrated into the existing wiring architecture. By combining the shield function with the substrate and insulating layers already present in the sensor, the design reduces parasitic capacitance without proportionally increasing overall device complexity.
Solution Approach 2:
The insulating films serve multiple functions: they provide electrical insulation for the wiring and simultaneously act as part of the shield structure. This multi-functionality reduces the need for separate components, thereby reducing parasitic capacitance while minimizing the increase in 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
The implementation of a shield part between the electrode wiring reduces parasitic capacitance, enhancing detection accuracy and reliability in physical quantity detection, while also simplifying the manufacturing process by using the same material for all components and avoiding short circuits through recessed wiring configurations.
Implementation Method 1
a first shield part is provided in at least one part between the fixed electrode wiring and the movable electrode wiring
Implementation Method 2
a physical quantity sensor including a base plate part sectioned by a cavity formed in a semiconductor substrate
Implementation Method 3
the physical quantity sensor is a capacitance change detection type
Data Source
AI summary
A physical quantity sensor includes a base substrate, a movable part located on the base substrate and provided on a principal surface of the base substrate, a movable electrode part provided in the movable part, and a fixed electrode part provided on the principal surface of the base substrate and located to be opposed to a movable electrode finger, and the fixed electrode part is connected to fixed electrode wiring provided at the principal surface side of the base substrate, the movable electrode part is connected to movable electrode wiring provided at the principal surface side of the base substrate, and a shield part is provided between the fixed electrode wiring and the movable electrode wiring.