»Regarding technical maturity, we have cutting edge technology« concludes Infineons’ Marketing Director Frank Bialas. He has just presented the semiconductor manufacturer's first CO2 sensor. Series production is scheduled to start in just over a year. The components are developed entirely by Infineon and are assembled at the companys plant in Malaysia.
According to Bialas, cutting edge means a smaller form factor and lower manufacturing costs. So low that they can exceed the price threshold for the mass market. This is around 10 US dollars for a sensor module. Of course, this is not enough for smartphones, but there is lively interest from the smart home and air conditioning sectors.
Infineon chose PAS
For the CO2 sensor, the Munich researchers use a photoacoustic approach (photoacoustic spectroscopy, PAS): a modulated IR light source radiates onto a gas mixture in a sample chamber. Existing CO2 absorbs the IR light, heats up and increases the pressure in the sample chamber. The pressure changes are measured by a MEMS microphone and allow conclusions to be drawn about the CO2 content.
The approach is less complex than Non Dispersive IR Spectroscopy (NDIR), which is also widely used. A smaller form factor is possible because a very high signal-to-noise ratio MEMS microphone (Xensiv IM69D130 with 69 dB SNR) is used. The application in the gas sensor is new; the first applications for the MEMS microphones were studio microphones and digital speech assistants.
Here the advantage of a high SNR value is immediately obvious. In a gas detector a high SNR microphone allows to measure very small pressure fluctuations, so that a small amount of gas is sufficient. The sample chamber can also be designed accordingly small. Overall, the sensor saves the developer 75 percent space compared to a standard sensor with comparable performance parameters.
The Xensiv PAS210 is an SMD device with integrated microcontroller and automatic baseline calibration (ABC). The technical parameters are specified as follows:
- Size: 13 x 12 x 6 mm³
- Measuring Range: 0 - 10,000 ppm
- Accuracy: 30 ppm
- Drift: < 1% per year (with active self-calibration)
- Lifetime: 10 years (pulsed operation)
- Power Supply: 12 V (IR emitter) + 3.3 V, 50 mA peak current
Evaluation boards have already been issued for selected customers, and they are expected to be launched on the free market in the first half of 2020. It will be demonstrated at the Sensor + Test from 25 to 27 June in Nuremberg.
»Needs our patents«
Infineon has been researching PAS technology for some time. Joint patents still exist from a collaboration with the Fraunhofer IPM. According to Infineon, the current sensor exclusively uses its own IP, with the MEMS microphones manufactured in Regensburg as the core element. »Anyone who wants to develop PAS gas sensors based on MEMS microphones needs our patents«, says Bialas. That's another reason why the company sees itself at the cutting edge.