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  5. MEMS Sensor Detects Airflows as Small as 1mm/second

MEMS Sensor Detects Airflows as Small as 1mm/second

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The human body constantly emits heat, and the air flow of this emission measures as little as 5mm per second. Even so, a 1.5mm x 1.5mm MEMS sensor can measure air flow as little as 1 mm per second. The best thing is that the smaller the MEMS sensor becomes, the higher the precision it offers and the less power it consumes. By taking advantage of these benefits of MEMS, OMRON is committed to developing a variety of MEMS devices, such as pressure sensors used in blood pressure monitors, gas meters, hot water supply units and other types of equipments and thermal flow sensors for measuring the flow of gases in fuel cells and respirators.

Thermal flow sensor used in respirators controls oxygen flow during surgical operations

Thermal flow sensor used in respirators controls oxygen flow during surgical operations.

The thermal flow sensor is designed to measure the flow of gases by detecting the temperature changes of the built-in heater. With its amazing ability to detect gas flows as minute as 1mm/second, this sensor is even capable of saving people's lives when incorporated in medical equipment.

OMRON's MEMS technology

OMRON's MEMS technology enables the creation of a very small chip measuring 1.5mm x 1.5mm x 0.4mm with an exceptionally high sensitivity that allows it to detect human breathing. To increase the sensing area and prevent heat from escaping, OMRON's thermal flow sensor uses a unique "crepe structure," which has an inverted trapezoidal dent formed through etching.

Crepe structure
ConventionalCrepe structure

  1. Traditionally, the etched-away bottom surface was used for sensing, thus it was necessary to increase the size of the silicon substrate itself if the sensing area was to be enlarged.
  2. OMRON's crepe structure is designed to minimize space that is wasted with conventional sensors. This allows the sensing area to be enlarged while maintaining the cubic volume of the silicon substrate at the same level as that of a conventional sensor.
What is etching?

Etching is a process to corrode the surface of a silicon wafer or other materials, or remove parts of them using chemical liquids or reactive ions. The two most common methods of etching are wet etching and dry etching. Wet etching is accomplished by immersing and dissolving the material in a chemical solution. With dry etching the material is dissolved to form deep grooves using the chemical reaction of special gases. Wet etching is less costly and more productive, while dry etching is more suitable if extremely fine fabrication is needed.

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