James L. Zunino

Thermochromism in polydiacetylene-metal oxide nanocomposites

Irreversible and reversible chromatic transitions during heating and cooling cycles were investigated in polydiacetylene poly-PCDA (poly-10,12-pentacosadiynoic acid) composites with nanocrystalline zinc oxide (ZnO), titanium oxide (TiO2), zirconium oxide (ZrO2) and ZnO and ZrO2 alloys. In contrast to pure poly-PCDA, poly-PCDA composites with nanocrystalline ZnO displayed rapid reversibility on thermal cycling, whereas the corresponding composites with nanocrystalline TiO2 and ZrO2 were irreversible, and poly-PCDA composites with thermally prepared ZnO and ZrO2 alloys displayed slower reversibility. The mechanism of reversible and irreversible thermochromism in these materials was explored using Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and X-ray absorption fine structure (XAFS) spectroscopy. In pure poly-PCDA, heating leads to an irreversible strain on the polymer backbone to form a red phase, which is not released on cooling. In the presence of ZnO evidence is provided for chelation involving the side chain head groups which can release strain on cooling to rapidly form the blue phase. Chemical interaction coupled with reversible behavior was however observed only when the composites were prepared with ZnO having an average crystallite size of 300 nm and below with a fraction of an amorphous grain boundary phase. Poly-PCDA composites with ZnO/ZrO2 alloys showing slower thermochromic reversibility can be used both as temperature and elapsed time-temperature sensors.

Department of Defense need for a micro-electromechanical systems (MEMS) reliability assessment program

As the United States (U.S.) Army transforms into a lighter, more lethal, and more agile force, the technologies that support both legacy and emerging weapon systems must decrease in size while increasing in intelligence. Micro-electromechanical systems (MEMS) are one such technology that the Army as well as entire DOD will heavily rely on in achieving these objectives. Current and future military applications of MEMS devices include safety and arming devices, guidance systems, sensors/detectors, inertial measurement units, tracking devices, radio frequency devices, wireless radio frequency identification (RFID), etc. Even though the reliance on MEMS devices has been increasing, there have been no studies performed to determine their reliability and failure mechanisms. Furthermore, no standardized test protocols exist for assessing reliability. Accordingly, the U.S. Army Corrosion Office at Picatinny, NJ has initiated the MEMS Reliability Assessment Program to address this issue.

Reliability testing and analysis of safing and arming devices for army fuzes

To address the lack of micro-electro-mechanical systems (MEMS) reliability data as well as a standardized methodology for assessing reliability, the Metallic Materials Technology Branch at Picatinny Arsenal has initiated a MEMS Reliability Assessment Program. This lack of data has been identified as a barrier to the utilization the MEMS in DOD systems. Of particular concern are the impacts of long-term storage and environmental exposure on the reliability of devices. Specific objectives of the Metallic Materials Technology Branch (MMTB) program include: • Identify MEMS devices to be utilized in weapon systems. • Determine the relevant categories of MEMS materials, technologies and designs in these applications • Assess the operational environments in which the military MEMS device may be utilized. • Analyze the compatibility of MEMS devices with energetic and other hazardous materials. • Identify physics of failure, failure mechanisms and failure rates. • Develop accelerated test protocols for assessing the reliability of MEMS according to the categories. • Develop of reliability models for these devices. • Conduct testing and modeling on representative devices of interest to Army and DoD. • Develop of a methodology and capability for conducting independent assessments of reliability that cannot be obtained from private industry. In support of this effort, some testing has been performed on prototype mechanical Safety and Arming (S&A) devices for the 25-mm XM25 Air Burst Weapon. The objective is to test the S&A as a representative device for the identification of potential failure modes and effects for devices of the same class. Information derived from this testing will be used to develop standardized test protocols, formulate reliability models and establish design criteria and to identify critical parameters in support of the S&A development effort. To date, Environmental Stress Screening (ESS) tests have been performed on samples of the device. Along with the ESS testing, a failure modes and effects analysis has been developed and reliability modeling is under way.

Hybrid approach to MEMS reliability assessment

Recent advances in MEMS technology have led to development of a multitude of new devices. However applications of these devices are hampered by challenges posed by limited understanding of their reliability particularly the impacts of long-term storage. Current trend in micro/nanosystems is to produce ever smaller, lighter, and more capable devices in greater quantities and at a lower cost than ever before. In addition, the finished products have to operate at very low power and in very adverse conditions while assuring durable and reliable performance. Some of the new devices are being developed to function at high operational speeds, others to make accurate measurements of operating conditions in specific processes. Regardless of their application, the devices have to be reliable while in use. MEMS reliability, however, is application specific and, usually, has to be developed on a case by case basis. This paper presents a hybrid approach/methodology particularly suitable to quantitative studies of various aspects in MEMS reliability assessment. The presentation is illustrated with selected examples representing an initial study of reliability of specific MEMS. By quantitatively characterizing performance of MEMS, under different operating conditions, we can make specific suggestions for their improvements. Then, using the hybrid approach/methodology, we can verify the effect of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS sensors, which will ensure that these sensors are operated at maximum performance, are durable, and are reliable.

Studies of the blue to red phase transition in polydiacetylene nanocomposites and blends

The conjugated polymeric backbone of polydiacetylenes (PDAs), comprising of alternating ene-yne groups, undergo intriguing stress-, chemical- or temperature-induced chromatic phase transitions associated with the disruption of the backbone structure and shortening of the conjugation length. PDAs, such as polymerized 10, 12 pentacosadiynoic acids (PCDA), when incorporated with inorganic oxides form nanocomposites and uniform blends with polymers. Blends of poly-PCDA with polymers, such as polyvinyl alcohol, polyvinylidene fluoride and cellulose increase the blue to red transition temperature without affecting the irreversibility of the red phase. However, the addition of zinc oxide to pure poly-PCDA makes the red phase highly reversible and substantially increases the blue to red transition temperature. The addition of TiO 2 to poly-PCDA on the other hand does not affect the irreversibility of the red phase and the chromatic transition temperature. In order to understand the atomic scale interactions associated with these changes in the chromatic transitions, we have investigated both the nanocomposites and polymer blends using Raman and Fourier-transform infrared spectroscopy, and extended X-ray absorption fine structure (EXAFS) measurements

Guidelines for reliability testing of microelectromechanical systems in military applications

Micro electromechanical systems (MEMS) and microsystems technologies are seeing increased consideration for use in military applications. Assets ranging from aircraft and communications to munitions may soon employ MEMS. In all cases, MEMS devices must perform their required functions for the duration of the equipments mission profile. Long-term performance in a given scenario can be assured through an understanding of the predominant MEMS failure modes. Once the failure modes have been identified, standardized tests will be developed and conducted on representative devices to detect the potential for these failures. Failure mechanisms for MEMS devices in severe environments may include wear and stiction. While corrosion is not usually a concern for commercial MEMS devices, as they are made primarily of silicon, other materials, including metallics, are being considered for MEMS to provide enhanced robustness in military applications. When these materials are exposed to aggressive military environments, corrosion may become a concern. Corrosion of metallic packaging and interconnect materials may also present issues for overall performance. Considering these corrosion and degradation issues, there is a need to implement standardized tests and requirements to ensure adequate long-term performance of MEMS devices in fielded and emerging military systems. To this end, Concurrent Technologies Corporation has been tasked by the U.S. Army to initiate efforts to standardize test methods that have been developed under previous activities. This paper presents an overview of the MEMS activities under the standardization effort and the MEMS reliability test guidelines that have been drafted as a first phase of this effort.

Thermal indicating paints for ammunition health monitoring

Thermochromic semiconductive polymers that change color in response to external stimuli, such as heat and radiation, can be utilized to monitor the temperature range and elapsed time profiles of stored and prepositioned munitions. These polymers are being tailored to create paints and coatings that will alert Army logistic staff of dangerous temperature exposures. Irreversible indication via color change in multiple thermal bands, 145 F - 164 F (63o-73°C), 165 F - 184 F (74° - 84° C) and over 185 F (>85°C) are possible with these thermochromic polymers. The resulting active coating can be visually inspected to determine if safe temperatures were exceeded. More detailed information, including cumulative time of exposure in certain temperature bands through changes in optical chromaticity describing the vividness or dullness of a color, can be assessed using a hand-held optical densitometer.

Microfabricated implantable pressure sensor for flow measurement

A RF wireless capacitive pressure sensor is developed. The sensor has integrated inductor with the pressure sensitive capacitor as LC circuit. The resonant frequency of the sensor changes as the capacitance changes with applied pressure. The sensor uses LPCVD silicon nitride as sensitive membrane and the residual stress of the membrane has been measure as 139MPa. The sensor has size of 10 mm × 4 mm × 0.5 um. The sensor presents a pressure sensitivity of 1.65 MHz/cmH2O in pressure range of 0-20 cmH2O. The deflection of different shape of membranes is discussed. The deflection of square membrane is 130% to circular membrane under same applied pressure.

Development of nondestructive testing/evaluation methodology for MEMS

Development of MEMS constitutes one of the most challenging tasks in todays micromechanics. In addition to design, analysis, and fabrication capabilities, this task also requires advanced test methodologies for determination of functional characteristics of MEMS to enable refinement and optimization of their designs as well as for demonstration of their reliability. Until recently, this characterization was hindered by lack of a readily available methodology. However, using recent advances in photonics, electronics, and computer technology, it was possible to develop a NonDestructive Testing (NDT) methodology suitable for evaluation of MEMS. In this paper, an optoelectronic methodology for NDT of MEMS is described and its application is illustrated with representative examples; this description represents work in progress and the results are preliminary. This methodology provides quantitative full-field-of-view measurements in near real-time with high spatial resolution and nanometer accuracy. By quantitatively characterizing performance of MEMS, under different vibration, thermal, and other operating conditions, specific suggestions for their improvements can be made. Then, using the methodology, we can verify the effects of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS, which will ensure that they are operated at optimum performance, are durable, and are reliable.

Microfabricated implantable flow sensor for medical applications

A RF wireless capacitive flow sensor is developed. The sensor has integrated inductor with the flow sensitive capacitors as LC circuit. The resonant frequency of the sensor changes as the capacitance changes with applied flow. The sensor uses LPCVD silicon nitride as sensitive membrane and the residual stress of the membrane has been measure as 139 MPa. The sensor has size of 10 mm × 4 mm × 0.5 μm. The sensor integrated two pressure sensors together and designed related to flow 5-20ml/hour. The deflection of different shape of membranes and the parameters of flow sensor sensitivity are discussed. The deflection of square membrane is 130% to circular membrane under same applied pressure.