Next; the sniffing smartphone? – Sensirion proposes multi-gas sensor ‘nose’
The sensor platform will allow phones to act as alcohol breathalysers and monitor air quality, amongst other applications, as part of the next stage of smartphone evolution, the company believes.
Moritz Lechner, co-CEO of Sensirion (Staefa Zurich), said that the company has working examples of multi-gas sensors and plans to ship samples to potential customers in the spring of 2014 with the aim of expanding production in 2015.
Sensirion, founded in 1998 as a spin off from the Swiss Federal Institute of Technology (ETH) in Zurich, has achieved success in multiple sectors through the use of its ‘CMOSens’ technology, which combines temperature and humidity sensors and the analysis electronics in a single chip.
Lechner said the multi-gas platform would also be based on CMOS process technology using an array of miniature metal-oxide semiconductor (MOS) detector sites. As well as targeting specific gases the multi-site sensor will allow a process of profile matching to indicate the likely presence of other gases and scents.
Conventionally a MOS gas sensor is based on a heated film of a metal oxide such as tin oxide. As the temperature rises different gas molecules are adsorbed on the oxide surface where they change its electrical resistance. With suitably designed and calibrated sensors it is possible to detect numerous different gases at various concentrations including CO, NOX, NH3, CO2, water vapor, ozone and volatile organic compounds (VOC).
Different metal-oxides show a different sensitivity to different gases. Similarly, doping a specific metal-oxide such as tin-oxide with other metal-oxides or trace elements can alter sensitivity. By producing an array of different metal-oxide "pixels" and measuring the resistance of each one against temperature and time it is possible to build up a signature profile for numerous gases. It also means that the sensor can also be "taught" to identify novel gases and scents. Such odors would be introduced to the sensor and the profile noted.
Lechner declined to say what metal-oxide materials Sensirion is using, or the size of the sensor array the company is using, but he said he is confident that smartphone makers will want to move into gas sensing.
The clear trend is to make electronic equipment more aware of situation and context, he said. "If you are in the smartphone the next question is the environment," Lechner said. If the camera is like the eyes then the microphone is like the ears and a gas sensor is like a nose for the equipment, he added. As Sensirion has design wins for its temperature and humidity sensors in the Samsung Galaxy S4 and Galaxy Note 3 the move to a multi-gas sensor is an obvious one. It is also made easier because it is necessary to take into account temperature and humidity, for which it can already produce readings.
Lechner said the gas sensor will be developed for groups of applications. "The first bundle is breath analysis, which includes alcohol testing and a bad-breath detector. The second bundle is air quality. Here you are not measuring CO2 but CO2-equivalents, usually VOCs. And the third bundle is profiling smells where you are not detecting a single gas but, for example, can you tell the difference between Pepsi and Coke?"
Lechner reckons the current consumption can be kept at levels acceptable to the phone makers. It is down at 0.2 mA for one reading per minute, which is fine for the mobile phone companies, Lechner said.
Sensirion plans to initially ship the multi-gas sensor in a 2 by 2mm package similar to one in which temperature and humidity sensors ship. To begin with customers want the two functions separate and modular so that they can be included separately in phones, but over time Lechner can imagine them migrating to a single package. In addition, Sensirion will provide software that is used to identify gases based on the profiles and temperature and humidity compensation.