MEMS Pressure Sensor Field Shield Layout for Surface Charge Immunity
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Solution Overview
Problem
Pressure sensors encapsulated in oil-filled packages are susceptible to surface charge accumulation, leading to severe offset drift due to charge coupling through the dielectric oil, which compromises the accuracy of the sensing element.
Innovation Solution
A pressure sensing element with a field shield and a field shield circuit is implemented, where the field shield is configured to apply a potential to the substrate and diaphragm, reducing the influence of external charge accumulation and signal leakage by fully covering the sensing sub-element, contact via, and interconnect with a passivation layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field shield is added to the pressure sensing element, then immunity to external charge is improved, but device complexity increases
Solution Approach 1:
The field shield is nested within the existing pressure sensing element structure, positioned between the sensing element and the oil-filled package environment. This nested configuration allows the shield to protect the sensing element from external charge coupling through the dielectric oil without requiring a completely separate external shielding structure, thereby improving reliability while minimizing the increase in device complexity.
Solution Approach 2:
The field shield acts as an intermediary component between the external charge environment (including charged plastic housing and electrostatic discharge sources) and the pressure sensing element. By introducing this intermediate shielding layer, external electrostatic charge is blocked from coupling to the sensing element through the dielectric oil, thereby improving immunity to external charge while adding only a single intermediate component to the device.
2Reliability
If the field shield covers the entire sensing element including interconnects, then charge coupling is reduced, but manufacturing complexity increases
Solution Approach 1:
The field shield is configured with local quality by providing different coverage areas: the first field shield covers the sensing element diaphragm and piezoresistive elements, while the second field shield extends to cover the interconnects and contact vias. This localized shielding approach targets specific areas most susceptible to charge coupling (the sensing elements and their electrical connections) without requiring complete coverage of the entire device, thereby improving charge coupling resistance while managing manufacturing complexity.
Solution Approach 2:
The field shield configuration transitions from a two-dimensional planar shield to a three-dimensional multi-layer structure that wraps around and covers the interconnects and contact vias. This dimensional extension ensures comprehensive coverage of all charge-sensitive components including the vertical interconnect paths, thereby improving charge coupling resistance while the multi-layer approach allows for systematic manufacturing processes.
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 significantly reduces signal offset drift, providing immunity against external charge accumulation and ensuring long-term output stability even under high static charge conditions, thereby enhancing the performance and reliability of the pressure sensor.
Implementation Method 1
a field shield disposed over the sub-element, the contact via and the interconnect, the field shield configured to reduce influence of charge accumulation on the sub-element during operation
Implementation Method 2
Typically, charge coupling occurs through polar alignment of molecules in the oil in response to an external field, and associated space charge accumulation at an interface of the sense element and the oil
Data Source
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AI summary
A pressure sensing element includes a sensing sub-element disposed on a diaphragm, the element including a shield disposed over the sub-element and configured to substantially eliminate influence of external charge on the sub-element during operation. A method of fabrication and a pressure sensor making use of the pressure sensing element are disclosed.