The novel NIST device is being developed as the foundation for miniature yet highly accurate gas sensors that can detect chemical and biological agents, industrial leaks and even signs of extraterrestrial life from aboard a planetary probe.
The tiny microhotplates—no wider than a human hair—are programmed to cycle through a range of temperatures. They can be coated with metal oxide films tailored to detect specific gas species. Airborne chemicals attach to the surface of the detector depending on the type of film and the temperature of the surface, changing the flow of electricity through the device, which serves as the "signature" for identifying both the type and concentration of the gas in the ambient air.
Accurate microhotplate temperature measurements are crucial for the discrimination and quantification of gas species, while reliable, long-term operation demands that the microhotplate's temperature sensors be either highly stable or able to sense when they've drifted, a functionality known as a "built-in self test" (BIST). As demonstrated for the first time in a paper in an upcoming issue of IEEE Electron Device Letters,* the new calibration method satisfies both requirements.
A portion of the polysilicon heater making up the microhotplate originally served as the device's temperature sensor. However, this sensor would slowly drift over time from its initial calibration. Within three months, the temperature readings were off by as much as 25 degrees Celsius at high temperatures.
The NIST engineers overcame this shortcoming by using data from two additional temperature sensors—a highly stable, thin-film platinum/rhodium thermocouple integrated in the microhotplate structure for one sensor and the thermal efficiency of the structure itself for the other. Comparing the temperatures reported by these two sensors provides the microhotplate with its internal monitoring system. As long as the absolute value of the difference between the reported temperatures remains below a specified threshold value, the average of the two readings is considered reliable. Should the difference exceed the threshold, the system reports an error.
The original polysilicon sensor still provides the microhotplate's initial temperature measurement, which is used to calibrate the other two sensors. With the complete "check and balance" system in place, temperature measurements are accurate to within 1.5 degrees Celsius.
Having successfully demonstrated the new temperature calibration system for their microhotplate, the NIST researchers are working on additional advancements for the technology. Next in line is the development of a built-in system for sensing contamination of the metal oxide films critical to the microhotplate's use in gas detection.
* M. Afridi, C. Montgomery, E. Cooper-Balis, S. Semancik, K.G. Kreider and J. Geist. Analog BIST functionality for microhotplate temperature sensors. IEEE Electron Devices, Volume 30, No. 9 (September 2009).
Michael E. Newman | EurekAlert!
Cryo-electron microscopy achieves unprecedented resolution using new computational methods
24.03.2017 | DOE/Lawrence Berkeley National Laboratory
How cheetahs stay fit and healthy
24.03.2017 | Forschungsverbund Berlin e.V.
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy