Stress-Decoupled MEMS Pressure Sensor via Eutectic Bonding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Micromechanical pressure sensors face challenges due to stress from assembly and connection technology, temperature-induced deformations, and intrinsic stress from sensor elements, which cannot be fully compensated for, leading to inaccurate signal readings.
Innovation Solution
A method involving a MEMS wafer with a silicon substrate and a first cavity, eutectic bonding with a second wafer, and a second cavity etched in the silicon substrate to create a stress decoupling structure, using a reactive ion deep etching process with anisotropic and isotropic phases to form a trapezoidal etching front, providing all-round clearance for the sensor membrane and reducing contamination and media access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a micromechanical pressure sensor is mounted on a circuit board and housed, then the sensor can be integrated into a system, but stress from packaging technology and temperature-induced deformations couple onto the sensor membrane, causing measurement errors
Solution Approach 1:
The sensor assembly is divided into functionally independent segments: the sensor membrane is mechanically decoupled from the circuit board and housing through a stress-relief structure. The membrane is supported by a substrate that isolates it from external stresses, creating separate stress zones that prevent coupling between packaging stresses and membrane deformation.
Solution Approach 2:
A substrate or support structure acts as an intermediary between the sensor membrane and the external environment (circuit board, housing). This intermediary absorbs and isolates mechanical stresses, thermal deformations, and adhesive stresses, preventing them from reaching the membrane while still allowing the membrane to respond to pressure changes.
2Measurement precision
If the sensor membrane is exposed on all sides for pressure sensing, then pressure measurement capability is improved, but the sensor becomes vulnerable to contamination and media access that cause false signals
Solution Approach 1:
A protective membrane or thin film encapsulation is applied over the sensor membrane. This protective layer acts as a barrier against contamination and unwanted media access while still allowing pressure transmission to the sensor membrane, maintaining measurement capability while reducing false signals from contaminants.
3Reliability
If eutectic bonding is used to bond the MEMS wafer to the second wafer, then bond strength and reliability are improved, but the manufacturing process complexity increases
Solution Approach 1:
Eutectic bonding is utilized, which exploits the phase transition phenomenon where two metals bond at a specific eutectic temperature. This phase transition approach provides strong, reliable bonds between the MEMS wafer and second wafer, with the bonding process occurring at a well-defined temperature point that facilitates process control despite the increased manufacturing 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 approach effectively reduces incorrect signals and improves the operating characteristics of the pressure sensor by creating a stress decoupling structure and protecting the sensor from external contaminants, while being cost-effective and allowing for efficient etching and media access.
Implementation Method 1
eutectic bonding a bottom side of the MEMS wafer comprising metallization elements for forming the eutectic bond to a first side of the second wafer
Implementation Method 2
a reactive ion deep etching process with anisotropic and isotropic phases to form a trapezoidal etching front
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a method for producing a micromechanical pressure sensor (100), comprising the steps: providing an MEMS wafer (10) having a silicon substrate (11) and a first cavity (13) formed therein under a sensor membrane (12); providing a second wafer (30); bonding the MEMS wafer (10) to the second wafer (13), and exposing a sensor core (12, 13, 13a) from the rear side, wherein a second cavity (18) is formed between the sensor core (12, 13, 13a) and the surface of the silicon substrate (11), wherein the second cavity (18) is formed by means of an etching process, which is carried out with etching parameters changed in a defined manner.