P3 - A Pneumatic Infrared Detector with Capactive Read-out Circuit
- Event
- SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Nürnberg - Band
- Proceedings IRS² 2011
- Chapter
- IP - Poster Session
- Author(s)
- M. Schossig, V. Norkus, G. Gerlach - Technische Universität Dresden (Germany)
- Pages
- 109 - 114
- DOI
- 10.5162/irs11/ip3
- ISBN
- 978-3-9810993-9-3
- Price
- free
Abstract
Common types of thermal infrared sensors are thermopiles, bolometers, pyroelectric detectors and Golay cells. Although the three former types have been miniaturized by using silicon micromachining and thin-film technology, the Golay cell has not been improved very much recently. Some miniaturized Golay cell type of sensors have been developed using silicon micromachining technology together with a tunneling displacement transducer or a capacitive detector as readout mechanism. Due to the high heat conductivity of silicon the performance of such an infrared pneumatic detector is reduced.
In our work, a miniaturized infrared detector based on the principle of the Golay cell has been developed which does not use silicon as a material for the gas chamber. This detector basically consists of a sealed cavity made up of lithium tantalate or sapphire and a capacitive displacement transducer. In the gas chamber the infrared radiation is absorbed by a silver-black coating resulting in a heating of the gas and, consequently, an increase of gas pressure. This pressure rise causes a membrane deflection which is detected capacitively by a parallel plane capacitor. The main advantages of a capacitive read-out mechanism over a tunneling displacement transducer are its simple realization and evaluation making it ideal for low-cost applications. We use an interface circuit based on a sigma-delta core which directly converts a capacitance into a digital word, at high resolution (2 aF Hz-1/2), high linearity (±0.01 %) and high accuracy (±4 fF). All necessary functions such as
sensor excitation, temperature sensor, voltage reference, etc. are included. This circuit has a 2-wire, I2C-compatible serial interface and allows the assembly of the complete infrared detector together with signal evaluation into a TO-8 package. The expected (theoretical) performance of such a miniaturized infrared pneumatic detector is calculated and compared to commercially available infrared detectors. The principle of operation could be confirmed with a prototype.