LIGA fabricated 19-element threshold accelerometer array

Abstract This paper reports the design, fabrication, packaging, and testing of a relay-type threshold accelerometer array. The array includes 15 different sense elements ranging from 10 to 150 g in 10 g increments, and triply redundant 20 and 100 g sense elements for a total of 19 elements. The devices were fabricated using a modified sacrificial LIGA technique that creates a 100-300 m thick nickel structure with gold plated contacts. The threshold accelerometer array was evaluated by measuring its response to an applied acceleration (using a centrifuge) and by using two built-in testing methods: a pull-in voltage test, and a transit time test. Unlike the pull-in voltage test, the transit time test is sensitive to variations in the proof mass and spring constant. The average results from the centrifuge test, pull-in voltage test, and transit time test are all within approximately 20% of the expected values that are analytically calculated. In addition to the relay-type threshold sensing, the devices permit non-discretized readout of the acceleration using an alternative sense mode, in which the capacitance between the test electrode and proof mass was measured. This measurement shows a sensitivity of 670 aF/g for a 50 g threshold accelerometer, which is also within 20% of theoretical estimates

Ultracompliant thermal probe array for scanning non-planar surfaces without force feedback

This paper describes an array of micromachined thermal probes for scanning thermal microscopy for which the structural design and choice of materials virtually eliminate the need for z-axis mechanical feedback in contact mode scans. The high mechanical compliance accommodates significant topographical variation in the sample surface and prevents damage to soft samples. Thin film metal bolometers are molded into tips at the end of each cantilever in the array, and are sandwiched between two layers of polyimide that serves as the structural material. The probes overhang a Si substrate on which they are fabricated. Since integrated actuators and accompanying circuitry are no longer required, the prospect of scaling from the present eight-probe version to large numbers of probes for high speed, high resolution thermal mapping of large areas with simple detection circuitry is enhanced. The scalability and performance of the eight-probe prototype are evaluated, addressing issues of speed versus resolution, and thermal and mechanical decoupling. The results demonstrate that contact mode scans can provide better than 2 µm spatial resolution at speeds greater than 200 µm s−1 and show a 6.5 bit topographical resolution over a 7 µm dynamic range. Line scans obtained with a single-shank probe suggest that there are good prospects of obtaining images showing a lateral spatial resolution of less than 50 nm.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49034/2/jmm5_1_033.pd

The strain capacitor: A novel energy storage device

A novel electromechanical energy storage device is reported that has the potential to have high energy densities. It can efficiently store both mechanical strain energy and electrical energy in the form of an electric field between the electrodes of a strain-mismatched bilayer capacitor. When the charged device is discharged, both the electrical and mechanical energy are extracted in an electrical form. The charge-voltage profile of the device is suitable for energy storage applications since a larger portion of the stored energy can be extracted at higher voltage levels compared to a normal capacitor. Its unique features include the potential for long lifetime, safety, portability, wide operating temperature range, and environment friendliness. The device can be designed to operate over varied operating voltage ranges by selecting appropriate materials and by changing the dimensions of the device. In this paper a finite element model of the device is developed to verify and demonstrate the potential of the device as an energy storage element. This device has the potential to replace conventional energy storage devices

I-GLAD: a new strategy for fabricating antibacterial surfaces

Abstract The paper uses inverted glancing angle deposition (I-GLAD) for creating antibacterial surfaces. Antibacterial surfaces are found in nature, such as on insect wings, eyes, and plant leaves. Since the bactericidal mechanism is purely physical for these surfaces, the antimicrobial resistance of bacteria to traditional chemical antibiotics can be overcome. The technical problem is how to mimic, synthesize, and scale up the naturally occurring antibacterial surfaces for practical applications, given the fact that most of those surfaces are composed of three-dimensional hierarchical micro-nano structures. This paper proposes to use I-GLAD as a novel bottom-up nanofabrication technique to scale up bio-inspired nano-structured antibacterial surfaces. Our innovative I-GLAD nanofabrication technique includes traditional GLAD deposition processes alongside the crucial inverting process. Following fabrication, we explore the antibacterial efficacy of I-GLAD surfaces using two types of bacteria: Escherichia coli (E. coli), a gram-negative bacterium, and Staphylococcus aureus (S. aureus), a gram-positive bacterium. Scanning electron microscopy (SEM) shows the small tips and flexible D/P (feature size over period) ratio of I-GLAD nanoneedles, which is required to achieve the desired bactericidal mechanism. Antibacterial properties of the I-GLAD samples are validated by achieving flat growth curves of E. coli and S. aureus, and direct observation under SEM. The paper bridges the knowledge gaps of seeding techniques for GLAD, and the control/optimization of the I-GLAD process to tune the morphologies of the nano-protrusions. I-GLAD surfaces are effective against both gram-negative and gram-positive bacteria, and they have tremendous potentials in hospital settings and daily surfaces

Vacuum microdevices

In the paper MEMS-type microsystems working in vacuum conditions are described. All the benefits and drawbacks of vacuum generated in microcavities are discussed. Different methods are used to produce vacuum in microcavity of MEMS. Some bonding techniques, sacrificial layer method or getter materials are presented. It is concluded that the best solution would be to invent some kind of vacuum micropump integrated with MEMS structure. Few types of already existing vacuum micropumps are shown, but they are not able to generate high vacuum. As the most promising candidate for miniaturization an orbitron pump was selected. The working principle and novel concepts of its construction are described. The most important part of the micropump, used for gas ionization, is a field-emission electron source. Results of a research on a lateral electron source with gold emissive layer for integration with a micropump are presented

The study of radiation effects in emerging micro and nano electro mechanical systems (M and NEMs)

The potential of micro and nano electromechanical systems (M and NEMS) has expanded due to advances in materials and fabrication processes. A wide variety of materials are now being pursued and deployed for M and NEMS including silicon carbide (SiC), III–V materials, thin-film piezoelectric and ferroelectric, electro-optical and 2D atomic crystals such as graphene, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS₂). The miniaturization, functionality and low-power operation offered by these types of devices are attractive for many application areas including physical sciences, medical, space and military uses, where exposure to radiation is a reliability consideration. Understanding the impact of radiation on these materials and devices is necessary for applications in radiation environments.Defense Threat Reduction Agency (DTRA) (Grant HDTRA1-15-1-0027)Defense Threat Reduction Agency (DTRA) (Grant HDTRA1-15-1-0035)Defense Threat Reduction Agency (DTRA) (Grant HDTRA1-15-1-0036)Defense Threat Reduction Agency (DTRA) (Grant HDTRA1-15-1-0039)Defense Threat Reduction Agency (DTRA) (Grant HDTRA1-15-1-0060