Insulated MEMS Pressure Diaphragm for Continuous Electrical Isolation

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Solution Overview

Problem

Existing MEMS pressure sensors face issues with incomplete or insufficient electrical insulation between the diaphragm and the substrate, leading to potential short-circuits and compromised sensor operation due to non-continuous or thin buried insulating regions.

Innovation Solution

A manufacturing process that forms a MEMS device with a diaphragm insulated by a buried cavity surrounded by a continuous insulating layer and a lateral insulating region, ensuring complete electrical isolation through controlled epitaxial growth, thermal annealing, and oxidation steps to create a tub-shaped diaphragm insulating structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a simple and economical process is used to manufacture the MEMS sensor with a buried cavity, then the manufacturing cost and complexity are reduced, but the electrical insulation between the diaphragm and substrate becomes insufficient or non-continuous

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidelectrical insulation reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The insulating structure is divided into two distinct segments: a buried insulating region formed by thermal oxidation of the cavity walls, and a lateral insulating region formed by depositing insulating material into trenches. This segmentation allows each region to be optimized independently for its specific function while together they provide complete electrical insulation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The lateral insulating region acts as an intermediary element that bridges the gap between the buried insulating region and the diaphragm structure. It provides the critical lateral electrical isolation that the buried cavity alone cannot achieve, ensuring complete insulation without requiring complex manufacturing processes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If the buried insulating region is made thinner to reduce manufacturing complexity, then the manufacturing process is simplified, but the electrical insulation becomes insufficient leading to potential short-circuits

Engineering Contradiction:

Improveinsulating structure complexityVSAvoidelectrical insulation continuity

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The solution transitions from relying solely on the vertical dimension (buried insulating region thickness) to incorporating the lateral dimension. The lateral insulating region extends horizontally to provide electrical isolation, allowing the buried insulating region to be thinner while maintaining overall insulation reliability through the added lateral dimension.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If the insulating structure is made more robust to ensure complete electrical insulation, then the electrical insulation reliability is improved, but the manufacturing process becomes more complex and costly

Engineering Contradiction:

Improveelectrical insulation reliabilityVSAvoidmanufacturing simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The manufacturing process merges standard semiconductor fabrication techniques (thermal oxidation, photolithography, etching, and CVD deposition) that are already widely available in the industry. By combining these conventional processes in a systematic sequence, the patent achieves robust electrical insulation without requiring specialized or complex manufacturing equipment.

Inventive Principle:

Principle #5Merging (Combining)

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 process ensures reliable electrical insulation without interruptions, resulting in a robust and cost-effective MEMS device with high yield and reduced failure risk.

Implementation Method 1

an epitaxial layer is grown on the initial wafer in a deoxidizing environment. The epitaxial layer (corresponding to the epitaxial layer 3) closes the trenches of both groups at the top

Methodology Applied

Scientific EffectEpitaxial growth: Epitaxy

Implementation Method 2

A thermal annealing step is then performed which causes a migration of silicon atoms, which tend to move to a lower surface energy position

Methodology Applied

Scientific EffectThermal annealing: Annealing

Implementation Method 3

The injected oxygen causes oxidation of the silicon surrounding the channels and the cavity, giving rise to a silicon oxide layer on the sides of the buried cavity 12 and forming the buried insulating region 17

Methodology Applied

Scientific EffectOxidation: Oxidation

Data Source

PatentUS12515942B2MEMS device comprising an insulated suspended diaphragm, in particular pressure sensor, and manufacturing process thereof

Publication Date: 2026.01.06 STMICROELECTRONICS SRL

AI summary

MEMS device formed in a semiconductor body which is monolithic and has a first and a second main surface. A buried cavity extends into the semiconductor body below and at a distance from the first main surface. A diaphragm extends between the buried cavity and the first main surface of the semiconductor body and has a buried face facing the buried cavity. A diaphragm insulating layer extends on the buried face of the diaphragm and a lateral insulating region extends into the semiconductor body along a closed line, between the first main surface and the diaphragm insulating layer, above the buried cavity. The lateral insulating region laterally delimits the diaphragm and forms, with the diaphragm insulating layer, a diaphragm insulating region which delimits the diaphragm and electrically insulates it from the rest of the wafer.