Pressure Sensing Core

MEMS pressure sensors are the absolute core and mainstream of modern pressure sensing technology. They represent a revolution in miniaturization, intelligence, and low cost.

 

MEMS, or Micro-Electro-Mechanical Systems, refers to miniature mechanical and electronic systems that are manufactured in bulk on silicon wafers using integrated circuit (IC) fabrication processes.

The core of a MEMS pressure sensor is a micrometer-scale silicon diaphragm. Pressure acting on this diaphragm causes it to deform. This deformation alters the electrical characteristics of integrated sensing elements, and by measuring these electrical changes, the pressure value can be derived. Based on the sensing principle, they are mainly divided into the following types:

• Principle: Piezoresistive elements are created on the silicon diaphragm via a doping process and connected to form a Wheatstone bridge. When the diaphragm deforms under pressure, the resistance values change, causing the bridge to output a voltage signal proportional to the pressure.
• Characteristics: Mature technology, simple structure, large output signal, low cost. It is the most common and economical type of MEMS pressure sensor. However, it is sensitive to temperature and requires temperature compensation.

• Principle: The silicon diaphragm acts as one capacitor plate, forming a miniature capacitor with another fixed plate. Pressure deforms the diaphragm, changing the distance between the two plates, thereby causing a change in capacitance.
• Characteristics: Low power consumption, high sensitivity, good temperature characteristics, strong overload resistance. Often used in low-power and low-pressure measurement fields.

• Principle: Pressure changes the stress in the silicon diaphragm, which alters the natural frequency of a miniature resonant beam fabricated on it. Pressure is sensed by measuring the frequency change.
• Characteristics: Very high accuracy, good stability, digital output (frequency). However, the structure is complex, the cost is high, and it is mainly used in high-end industrial and aerospace fields.

MEMS pressure sensors are manufactured on silicon wafers using standard semiconductor processes (such as photolithography, etching, diffusion, thin-film deposition). The key step is forming the cavity and pressure diaphragm, typically using bulk micromachiningor surface micromachining techniques.

Compared to traditional mechanical or metal diaphragm pressure sensors, MEMS pressure sensors have overwhelming advantages:

• Miniaturization: Size can be as small as millimeter or even micrometer scale, making them easy to integrate.
• Mass Production & Low Cost: Manufactured simultaneously in thousands on wafers, just like chips, drastically reducing the cost per sensor.
• High Accuracy & High Reliability: No moving parts, long fatigue life.
• Low Power Consumption: Particularly suitable for battery-powered portable devices.
• Intelligence: Signal conditioning circuits, microprocessors, temperature sensors, etc., can be easily integrated on the same chip as the sensing unit, forming a "System-on-Chip" to achieve self-compensation, self-calibration, and digital output.

The reference pressure is a vacuum. It measures pressure relative to a perfect vacuum.

Applications: Altimeters, weather stations, vacuum systems.

The reference pressure is the current atmospheric pressure. It measures pressure relative to atmospheric pressure. Typically has a vent hole in the housing.

Applications: Blood pressure monitors, barometers, industrial process control (e.g., pipeline pressure).

Applications: Flow measurement, filter clogging monitoring, liquid level measurement.

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