In this paper we demonstrate the potential for novel nanoporous framework materials (NFM) such as metal-organic
frameworks (MOFs) to provide selectivity and sensitivity to a broad range of analytes including explosives, nerve
agents, and volatile organic compounds (VOCs). NFM are highly ordered, crystalline materials with considerable
synthetic flexibility resulting from the presence of both organic and inorganic components within their structure.
Detection of chemical weapons of mass destruction (CWMD), explosives, toxic industrial chemicals (TICs), and volatile
organic compounds (VOCs) using micro-electro-mechanical-systems (MEMS) devices, such as microcantilevers and
surface acoustic wave sensors, requires the use of recognition layers to impart selectivity. Traditional organic polymers
are dense, impeding analyte uptake and slowing sensor response. The nanoporosity and ultrahigh surface areas of NFM
enhance transport into and out of the NFM layer, improving response times, and their ordered structure enables structural
tuning to impart selectivity. Here we describe experiments and modeling aimed at creating NFM layers tailored to the
detection of water vapor, explosives, CWMD, and VOCs, and their integration with the surfaces of MEMS devices.
Force field models show that a high degree of chemical selectivity is feasible. For example, using a suite of MOFs it
should be possible to select for explosives vs. CWMD, VM vs. GA (nerve agents), and anthracene vs. naphthalene
(VOCs). We will also demonstrate the integration of various NFM with the surfaces of MEMS devices and describe
new synthetic methods developed to improve the quality of VFM coatings. Finally, MOF-coated MEMS devices show
how temperature changes can be tuned to improve response times, selectivity, and sensitivity.
Maintaining the integrity of the internal atmosphere of a hermetic device is essential for long-term component reliability because it is within this environment that all internal materials age. As MEMS package sizes decrease with miniaturization, characterization of the internal atmosphere becomes increasingly difficult. Typical transistor metal cans (e.g., TO-5 type) and large MEMS devices have internal volumes of tenths of a milliliter. Last year, gas-sampling
methods for smaller-sized MEMS packages were developed and successfully demonstrated on volumes as low as 3 microliters (package outside dimensions: ~1 x 2 x 5 mm). This year, we present gas sampling methods and results for a much smaller MEMS package having an internal volume of 30 nanoliters, two orders of magnitude lower than the previous small package. After entirely redesigning the previous sampling manifold, several of the 30 nanoliter MEMS
were gas sampled successfully and results showed the intended internal gas atmosphere of nitrogen was sealed inside the package. The technique is a radical jump from previous methods because not only were these MEMS packages sampled, but also the gas from each package was analyzed dozens of times over the course of about 20 minutes. Additionally, alternate methods for gas analyses not using helium or fluorinert will be presented.
Chemical and physical materials-aging processes can significantly degrade the long-term performance reliability of dormant microsystems. This degradation results from materials interactions with the evolving microenvironment by changing both bulk and interfacial properties (e.g., mechanical and fatigue strength, interfacial friction and stiction, electrical resistance). Eventually, device function is clearly threatened and as such, these aging processes are considered to have the potential for high (negative) consequences. Sandia National Laboratories is developing analytical characterization methodologies for identifying the chemical constituents of packaged microsystem environments, and test structures for proving these analytical techniques. To accomplish this, we are developing a MEMS test device containing structures expected to exhibit dormancy/analytical challenges, extending the range of detection for a series of analytical techniques, merging data from these separate techniques for greater information return, and developing methods for characterizing the internal atmosphere/gases. Surface analyses and data extraction have been demonstrated on surfaces of various geometries with different SAMS coatings, and gas analyses on devices with internal free volumes of 3 microliters have also been demonstrated.