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MEMS-CMOS gas sensor makes its way to smartphones

Posted: 09 Nov 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Cambridge CMOS Sensors? smartphone? gas sensor? CMOS? MEMS?

The very top layer of the chip has a metal-oxide layer (such as tin-oxide for VOCs) with gold contacts beneath it that measure the resistance of the metal oxide. Underneath the gold interconnections is the tiny hot plate that heats the whole assembly, thereby changing the resistance of the top layer in direct proportion to the gas coming in the package (through a hole).

The latest digital version then uses a Silicon Labs 8051 MCU (housed in the same package as the MEMS-CMOS die) to measure the resistance between the gold electrodes and buffer its changes in real time. When it passes a given level, an alarm interrupt is sent to the application processor in the smartphone (or the application processor polls the 8051 periodically to empty its buffer and draw a parts-per-million, PPM, graph of air quality, for instance, depending upon the app being run).

MEMS-CMOS wafers

MEMS-CMOS wafers can be diced into hundreds of 1mm2 die packaged in standard 2.7mm x 4mm packages which can hold multiple different types of gas sensors. (Source: Cambridge CMOS Sensors, used with permission)

Five-year battery lifetimes are easy to attain with small lithium batteries with the current model. The package size today is 2.7mm x 4mm x 0.6mm to hold both the CCS811 and 8051 in a land-grid array package and I2S interface using less than 1.2mW when active and less than 6?W in idle mode.

Cambridge previously had an analogue version that required the OEM to add its own MCU or, alternatively, to waste valuable application processor cycles turning on the micro hotplate, measuring the resistance between the gold electrodes and analysing the results. The CCS811 digital model, however, is expected to allow the gas sensor to penetrate the billion unit mass market for smartphones, wearables and Internet of Things (IoT) devices.

Jess Brown introduces the gas sensor

A director at Cambridge CMOS Sensors Jess Brown introduces the gas sensor that China is using to one-up the Apple iPhone. (Source: EE Times)

Founded in 2008, Cambridge CMOS Sensors took six years to develop its analogue version, but only a year to follow up with digital. Next they are going to house multiple CCS811 die in the same package to sense a whole variety of gases to serve consumer and industrial sensor networks, as well as other mass markets that need small ultra-low-power gas sensors.

- R. Colin Johnson
??EE Times


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