What are Inertial Sensors?

High-precision inertial sensors are used to measure the inclination, acceleration and vibration of a technical application. These can be small MEMS, or Micro Electromechanical Systems, that have a single crystal silicon sensor element as a basis, and are produced with the latest micromechanical manufacturing processes.

The micromechanical processes used for the production of these systems can vary, but they all have their strengths. New micromechanical processes for MEMS production were developed by First Sensor. The innovative product series that was launched includes inertial sensors that incorporate the advantages of the previous versions.

This resulted in enhanced performance features, highly improved price-performance ratio and the creation of new applications, particularly in the fields of geoengineering, condition monitoring, navigation and robotics.

MEMS – Micro Electromechanical System: What a High-Precision Accelerometer Can Do

Miniaturized MEMS sensors allow the measuring of accelerations in all three spatial dimensions.

MEMS inertial sensors are advanced products that have proven to be extremely robust, reliable, fast and temperature-stable. They also have the ability to detect even the smallest changes in position and acceleration.

The image presents the extremely high resolution that the inclinometer can achieve. It is possible to detect even the deflection of a 10 meter long board by a single human hair with a diameter of 100 µm. This corresponds to a deflection of only 0.0005° (2 arcsec or 10 µm/M).

The Future is Digital

A key technology of the Internet of Things is the MEMS sensor technology. Due to the continuous digitalization, miniaturized accelerometers and inclinometers are also likely to continue their development. For instance, inertial sensors will be intelligently programmed in the future, and will have microcontrollers, miniature batteries or tiny radio chips that would allow them to send their measurement data online.

Areas where the high-precision inertial sensors from First Sensor are currently applied:

  • Condition monitoring of buildings
  • Monitoring of wind power and solar energy plants, high-voltage lines, dams, pipelines, etc.
  • Monitoring of Oil & Gas on/off-shore infrastructures, nuclear, gas and hydropower plants, etc.
  • Systems for stabilization and alignment
  • Infrastructure and transport
  • Navigation

Mini Format, Mini Production Costs, Mini Operating Costs: Capacitive Inertial Sensor and the Technical Concept Behind It

MEMS inertial sensors that make the capacitive measurement of inclination, acceleration and vibration possible rely on advanced micromechanical manufacturing processes and on a tiny silicon sensor. These form a spring-mass system, which contains structures with a width of just a few µm.

During acceleration, masses suspended on springs are deflected. This allows for a measurement of the change in capacity. An ASIC reads this change in capacity and transmits the measured value.

During the process of sensor production, masses and springs are separated from the silicon. These structures often have a thickness of only a thousandth of a millimeter.

Due to the micro format, MEMS can be produced in large quantities and consume little energy.

Technical Components of a MEMS Inertial Sensor

  • Monocrystalline silicon sensor
  • High-performance ASIC
  • Housing for both chips

MEMS Performance Data from First Sensor

. . .
Measurement ranges ±30° ±3 g, ±8 as well as ±15 g
Noise density less than 0,0004°/√Hz less than 30 µg/√Hz
Resolution less than 0,0015° less than 40 to 95 µg
Measurement frequency > 6 Hz > 6 Hz

 

The Heart of the Sensor: The Monocrystalline Silicon Sensor

The heart of every MEMS is a silicon sensor, which is usually manufactured in bulk or in a surface micro-machining process. However, First Sensor is already applying new technologies called the HARMS (High Aspect Ratio Microstructures) process and the AIM (Air Gap Insulated Microstructures) process.

The former minimizes cross sensitivities by enabling microstructures with a high aspect ratio. The latter isolates the components by using an air gap, and thus, minimizes parasitic capacitance. The result is MEMS that offer more advantages than all traditionally manufactured inertial sensors combined.

Advantages of the First Sensor MEMS inertial sensors in measuring acceleration, inclination and vibration:

  • Flexible MEMS design: the range of a measurement is from 1 to 15 g
  • Four standard sensors: four different measurement ranges; optimum adaptation to the range (spring-mass principle)
  • Measurement of two axes with one sensor: easy to use
  • Silicon microstructures with high aspect ratio: ultra-low transverse axis sensitivity; fatigue-free; long-term stable sensor
  • Air-gap-isolated microstructures: limited parasitic capacitance; limited mechanical stress due to the lack of SiO2 layers; exceptional temperature stability; easy calibration

Direct Comparison of MEMS Technologies

Surface micro-machining HARMS/AIM technology Bulk micro-machining
In plane displacvement and
out of plane displacement
In plane displacement Out of plane displacement
Maximum of three axes per chip Typically two axes per chip One axis per chip
Small chip Medium to large chip Large chip
Low etching depths (cost-effective) Deep etched structures (cost-intensive) Deep etched structures (cost-intensive)
Small seismic masses Medium to large seismic masses Large seismic masses
Small capacitors (small capacitive detection range) Large capacitors (large capacitive detection range) Large capacitors (large capacitive detection range)
Low signal-to-noise ratio Low noise, high signal-to-noise
ratio
Low noise, high signal-to-noise ratio
Low stability High stability High stability
Low costs Medium costs High costs
For consumer goods such as smartphones and applications in automotive engineering such as airbag deployment etc. For middle and upmarket market segments such as industrial automation, geoengineering, condition monitoring, navigation, robotics etc. For upmarket market segments such as aviation and space travel

 

Sensor Brain: The High-Performance ASIC

As mentioned, the silicon sensor is the core of the MEMS inertial sensors. In addition, ASIC is the brain. The integrated circuit reads the capacitive signals of the sensor element and transmits the measured value digitally.

Features of a high-performance ASIC:

  • Very low-noise capacitive detection
  • High-resolution with high dynamic range
  • Optimal support for nominal and differential capacitance range
  • Flexible signal filter
  • Digital SPI interface (configuration of the sensor ASIC system, readout of sensor data)

Sensor Housing: The Hermetically Sealed Housing

The housing that encloses the two chips must not only allow the sensor to perform, but must also be cost-effective to produce and implement.

Features of the MEMS housing:

  • In-house design that can be adjusted to fit a variety of applications
  • Hermetically sealed housing
  • Ceramic substrate
  • Cost-effective production of small and medium quantities

 

This information has been sourced, reviewed and adapted from materials provided by First Sensor AG.

For more information on this source, please visit First Sensor AG.

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