![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20081108110537im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Final Report: MEMS-Based Volatile Organic Compound Monitor
EPA Contract Number: EPD04014Title: MEMS-Based Volatile Organic Compound Monitor
Investigators: Doppalapudi, Dharanipal
Small Business: Boston MicroSystems Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: March 1, 2004 through August 31, 2004
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2003)
Research Category: Air Quality and Air Toxics , SBIR - Monitoring Technologies for Volatile Organic Compounds , Small Business Innovation Research (SBIR)
Description:
Summary/Accomplishments (Outputs/Outcomes):In phase I, Boston MicroSystems demonstrated the technical feasibility of developing a VOC monitor by achieving each of the technical objectives. Arrays consisting of 8 SiC-AlN MEMS resonators were fabricated with refined design and processes. The new design resulted in a larger and stiffer MEMS structures. Piezoelectric AlN layer deposition by MBE was optimized to reduce the residual stresses, thereby improving the performance, stability and yield of the resonators. The fabricated dies were packaged to facilitate polymer film deposition as well as sensor testing. In collaboration with NRL, an ink-jet process was used to deposit different polymer films selectively on to individual microresonators such that each array consists of multiple resonators each sensitive to different VOCs. A sensor testing apparatus was built to enable monitoring of all 8 resonators of the array simultaneously, as the sensor is exposed to different gases of varying concentrations in an inert gas background. The presence of benzene, toluene and dimethyl chloride was detected using the sensor array, by monitoring the shift in the resonance frequency caused by polymer absorption of the gases.
The proof-of-concept VOC sensor prototypes fabricated and tested in Phase I clearly demonstrate the feasibility for sensitive VOC detection using polymer coated microresonator arrays. In particular, the following important capabilities have been demonstrated:
- detection time constants better than 90 seconds (limited by the sensor test and gas delivery system). Note: recovery times (when VOC was removed) were significantly longer when the sensor array was operated at room temperature, as is consistent with polymer coated SAW-based VOC sensors which are often heated to 35-45(C
- detection of low ppm levels of three priority VOCs, to at least 45 ppm benzene, 3 ppm toluene, and 57 ppm dimethyl chloride. Note: for toluene and methyl chloride, the polymer coated resonators were still saturated at these levels (i.e. they did not exhibit greater resonant frequency shifts with increasing VOC concentration), while benzene appeared to be saturated above ~100 ppm. Testing at lower concentrations was not feasible with our existing experimental setup, however dilute 100 ppm mixtures of these gases have now been ordered to extend testing down to 50 ppb levels.
- selectivity of polymer coated resonators to different analytes: the saturation detection level of dimethyl chloride, benzene and toluene, as measured with the same PECH coated resonator, were 350, 550 and 100 Hz respectively, demonstrating significantly lower affinity of this PECH coated resonator to toluene than the other two compounds.
- the ability to eliminate cross sensitivities by comparing the response to a reference resonator on the array. This was expected to be a strong advantage of these MEMS resonator arrays: the sensing and reference resonators are all fabricated on a small ~3.5 mm chip on high thermal conductivity SiC substrates, thereby effectively maintaining each resonator in the array at the same temperature and pressure.
Our phase I results already show low ppm VOC detection levels (to at least 45 ppm benzene, 3 ppm toluene, and 57 ppm dimethyl chloride), approximately in the range required for occupational safety applications. With further refinements and integration with pattern recognition algorithms in phase II, we have no doubt the proposed MEMS-based Volatile Organic Compound Detector will exceed these requirements, and provide highly sensitive, selective and portable detection capabilities to EPA, first responders, industry and society.
Conclusions:In phase I, we demonstrated the technical feasibility of this approach, by fabricating packaged arrays consisting 8 SiC-AlN MEMS resonators, selectively depositing three different chemoselective polymer coatings onto individual resonators in the arrays [3], and demonstrating benzene, toluene and methylene chloride detection capability of better than 45 ppm, 3ppm and 57ppm levels respectively, even with the non-optimized proof-of-concept phase I prototypes. Furthermore, exceptionally effective methods were developed and demonstrated for virtually eliminating cross-sensitivities to temperature and pressure variations using reference resonators in the array, and capability / evidence for discrimination between specific compounds was shown.
References:
- Health Effects Notebook for Hazardous Air Pollutants, EPA: http://www.epa.gov/ttnatw01/hlthef/hapindex.html
- Sources of HAP emissions, EPA: http://www.epa.gov/ttn/atw/nata/pollinf2.html
- With the assistance of the US Naval Research Laboratory (Dr. Eric Houser, Surface Modification Branch, Materials Science and Technology Division)
No journal articles submitted with this report: View all 1 publications for this project
Supplemental Keywords:Homeland security first responders (hazmat and fire service), indoor air quality, HVAC controls, occupational safety in petrochemical, construction, manufacturing and mining industries, process control, electronic nose, quality control,
,
Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Scientific Discipline, RFA, Analytical Chemistry, Chemicals, Atmospheric Sciences, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, aerosol analyzers, chemical characteristics, Volatile Organic Compounds (VOCs), HAPS, micro electromechanical system, real-time monitoring, aromatic compounds, atmospheric chemistry, Phenol, microsensors, microanalyzer
Progress and Final Reports:
Original Abstract