Technology

Chemoresistive measurement principle

Metal-oxide gas sensors are based on a film of metal-oxide particles between two electrodes, located on top of a hotplate. Heating the metal oxide yields negatively charged oxygen species absorbed on the metal-oxide surface. The surface oxygen species react with ambient target gases and thereby release electrons into the metal-oxide film resulting in a change of electrical resistivity of the metal-oxide layer. The change of resistivity is measured between the two electrodes and directly depends on the ambient target gas concentration.

Multi-pixel gas sensing platform

The multi-pixel gas sensing platform integrates four metal oxide sensing layers – known as “pixels” – in a very small DFN package. It offers an entire sensor system on a single chip featuring a digital I2C interface that can be directly connected to a microcontroller, enabling swift and cost-effective design-in. Four individual temperature-controlled micro hotplates ensure stable operation of the four sensor pixels. The pixels’ sensor signals are pre-processed into digital signals by on-chip algorithms.

MOXSens® technology

Combining optimized metal oxide sensing layers with Sensirion’s multi-pixel gas sensing platform results in a unique resilience to siloxane-induced contamination. Sensirion’s MOXSens® technology enables highly sensitive and reliable gas measurement of air pollutants, e.g. volatile organic compounds (VOCs) in indoor air environments.

Transmissive non-dispersive infrared (NDIR)

CO₂ molecules absorb specific wavelengths of infrared (IR) light. NDIR CO₂ sensors pass IR light through a measurement cell, using a detector to measure how much light is transmitted through it (i.e. not absorbed by CO₂ molecules). By comparison to a reference light intensity, CO₂ concentration is derived. Two types of NDIR CO₂ sensors exist: single and dual channel. The reference measurement channel in dual channel NDIR enhances long-term stability.

Dual-channel principle

The SCD30 is based on the dual-channel measurement principle. Thanks to the built-in reference channel, sensor drifts are corrected automatically, resulting in excellent long-term stability of the sensor. The exceptional measurement accuracy is realized thanks to Sensirion CMOSens detectors. The thin design of the sensor is made possible by integrating the measuring cell into the PCB. In addition to CO₂ concentration, the SCD30 measures ambient humidity and temperature thanks to the integrated humidity sensor.

Photoacoustic NDIR (PA)

PA uses a pulsed IR light source that emits wavelengths absorbed by CO₂. Absorption of light by CO₂ molecules leads to additional molecular vibration, increasing the pressure in the measurement cell. As the light source is pulsed, this pressure increase occurs periodically, creating an acoustic wave. The more CO₂ molecules present, the larger the amplitude of the acoustic wave. This is measured by a microphone to calculate CO₂ concentration. 

PASens® Technology

The innovative PASens® Technology is based on Sensirion's experience in realizing high integration of environmental sensors:

• High energy efficiency and exceptional long-term stability are enabled thanks to Sensirion's MEMS IR emitter.
• The integrated humidity sensor enables accurate CO₂ measurements over a wide relative humidity and temperature range. 
• Highest accuracy and lowest noise values are achieved thanks to the optimized signal processor. 
• Unbeatable sensor robustness is realized thanks to the metal cap covering all sensor components.

Thermal conductivity

TC is based on the inherent thermal conductivity of all gases. With a thorough understanding of the gas compo­sition in ambient environments, subtle changes in gas con­centrations can be detected. The measurement principle is based on heating the air within a measurement cavity and sensing the heat transfer with a temperature sensor.

Wide measurement range

Based on Sensirion’s CMOSens® Technology and thermal conductivity (TC) measurement principle, our CO₂ sensors cover a wide measurement range. The fully calibrated STC31-C enables highly accurate measurements of CO₂ concentrations up to 100% in air, making it ideal for high-concentration applications such as breath analysis or leakage detection. The compact STCC4 complements this by providing precise monitoring of typical indoor CO₂ levels, supporting applications such as air quality and ventilation control. Both sensors include built-in compensation algorithms using external sensor data to account for temperature, humidity, and pressure, ensuring accurate and reliable CO₂ measurements across a broad range of applications.

Exceptional response time / Low Power Mode

The optimized sensor geometry enables very fast response times, as only a small amount of gas needs to diffuse between the heater and the temperature sensor to trigger a temperature change. At the same time, the integration of all functions on one chip and the high sensitivity of the temperature sensor enables a "low power mode", which allows installation in battery-powered devices.

Optical (laser based) measurement principle

This measurement principle is based on laser light scattering. Airflow is generated inside the sensor with the aid of a fan. This airflow carries particulate matter in the ambient air from the inlet of the sensor to the outlet. Near the photodiode, the particles in the airflow pass through a focused laser beam, scattering the laser’s light. A photodiode converts this scattered light into an electrical signal, which is then converted on the internal microcontroller into an output value for the matter’s mass and concentration using algorithms.

Dust resistance

Based on more than 20 years of experience in designing flow sensors for numerous demanding markets and applications, Sensirion’s engineers have developed innovative and proprietary flow guidance technology. With its help, dust and dirt deposits on the optical components are avoided and exceptional long-term stability is made possible. 

Performance

Sensirion’s proprietary algorithms use a new concept that allows size classes to be determined regardless of particle type, significantly improving the measurement of mass concentration. This provides greater accuracy in distinguishing aerosols and enables exceptionally precise measurement in a wide range of environmental conditions. 

Electrochemical measurement principle

The SFA30 is based on an amperometric electrochemical measurement principle that enables minimum cross-sensitivity and excellent long-term stability. At the working electrode, formaldehyde is decomposed and an electrical current flows between the counter electrode and the working electrode. The current is proportional to the formaldehyde concentration. Thanks to the Sensirion-specific chemistry, the sensor is selective to formaldehyde with respect to other VOCs.

Thermal measurement principle

The liquid flow is determined via a thermal measurement principle. A controllable heating element is located in the center of a pressure-stable membrane, and a temperature sensor is mounted symmetrically upstream and downstream of it in the direction of flow. Any flow through this membrane causes the thermal transfer of heat to the downstream temperature sensor, thus generating a precisely measurable signal due to the resulting difference in temperature. The microthermal flow sensor is integrated by etching this pressure-stabilized and glass-passivated membrane into the silicon chip.

Temperature compensation and complete calibration

The chip contains a temperature sensor with a signal that compensates for any temperature effects that may occur. This eliminates the need to install additional correction sensors, and consequently makes Sensirion’s technology a very cost-effective and space-saving solution. In addition, a digital process circuit and a memory cell are integrated on the chip to store the calibration data. Each Sensirion sensor is individually calibrated during production. The signal is therefore fully calibrated, linearized and temperature compensated at all times.

High stability and reliability

The liquid sensors based on CMOSens® technology offer a variety of advantages and impress with outstanding stability, reliability and repeatability. The calibrated and stable sensors for a wide range of applications enable very precise and fast measurements from low (100 ml/min) to very low (nl/min) flow rates.

Thermal measurement principle

The mass flow is determined via a thermal measurement principle. A controllable heating element is located in the center of a pressure-stable membrane, and a temperature sensor is mounted symmetrically upstream and downstream of it in the direction of flow. Any flow over this membrane causes the thermal transfer of heat to the downstream temperature sensor, thus generating a precisely measurable signal due to the resulting temperature difference. The microthermal flow sensor is integrated by etching this pressure-stabilized and glass-passivated membrane into the silicon chip.

High sensitivity and bidirectional measurements

The CMOSens® gas flow sensors outperform conventional sensors with piezoresistive membranes in terms of sensitivity to low flow rates or pressure differences, offset drift and hysteresis, position sensitivity, shock resistance and temperature fluctuations. All sensors measure bidirectionally.

Temperature compensation and complete calibration

The chip contains a temperature sensor with a signal that compensates for any temperature effects that may occur. This eliminates the need to install additional correction sensors, and consequently makes Sensirion’s technology a very cost-effective and space-saving solution. In addition, the chip contains a digital process circuit and memory for calibration data. Each Sensirion sensor is individually calibrated during production. The signal is therefore fully calibrated, linearized and temperature compensated at all times.

Various sensor solutions

Based on the thermal measurement principle, Sensirion offers different gas flow sensor solutions: flow sensors, mass flow controllers, differential pressure sensors. The individual sensor solutions differ in the effort required for integration into the customer system. Liquid flow sensor solutions or even controller solutions are particularly suitable for projects with medium and small quantities. A plug-and-play solution is advantageous in these cases, as it helps to get the product to market quickly. For high-quantity applications or applications with special form factor requirements, a differential pressure sensor in a bypass configuration is the best choice.