TMOS thermal sensor provides PIR alternative ...

Jul 13, 2023

The sensor can be used for human-presence and -motion detection in security systems, home-automation equipment, and IoT devices, the company said. While the device is based on “thermal MOSFETs” and can outperform passive infrared (PIR) sensors there is another competing passive technology.

The STHS34PF80 sensor contains thermal transistors that can detect stationary objects, unlike conventional PIR detectors that require the detected object to be moving to produce a measurable response from the sensor. Also, while PIRs need a Fresnel lens to sense moving objects, ST’s novel detector allows simpler, lens-free construction.

The STHS34PF80 contains thermal MOSFETs (TMOS) that are sensitive to the heating effects of infrared radiation incident on their gates, as well as digital readout circuitry integrated efficiently on the same chip using silicon-on-insulator (SOI) CMOS technology.

The SOI is used to facilitate micromachining to thermally isolate the TMOS for accurate temperature sensing.

Infrared radiation in a field-of-view reaches a transistor gate that is thermally-insulated using MEMS fabrication. The IR energy alters the bias of the MOS transistor and is used to sense the temperature of objects or people. The TMOS is powered at a sub-threshold voltage below that needed to turn the transistor fully on. In this mode, the drain-source current is highly temperature dependent and produces an accurately measurable response to minimal infrared radiation. This enables the sensor to detect human presence, via infrared emissions, whether the person is moving or still.

“Our new STHS34PF80 is an economical, ultra-low-power sensor that lets building automation operate consistently whether detected occupants are moving or not. It’s made using an innovative combination of CMOS chip fabrication, silicon micromachining, and low-voltage circuit design capabilities,” said Simone Ferri, general manager of the AMS MEMS sub-group at ST, in a statement.

A startup company called Zepsor Technologies Inc. (Burlington, Mass.) has developed something similar, although its technology is entirely passive (see Zepsor presents zero-power IR sensors). In essence what Zepsor have done is build a light-activated micromechanical relay. The demonstration is a sensor that can detect the thermal energy generated by a person or other body.

The STHS34PF80 is in production now and available in a 10-lead land-grid array (LGA) package, priced from US$2.60 for orders of 1,000 pieces.

www.st.com

www.zepsor.com

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