Jianmin Miao

Studies of digital microscopic holography with applications to microstructure testing

We propose an in-line digital microscopic holography system for testing of microstructures. With the incorporation of a long-distance microscope with digital holography, the system is capable of imaging test microstructures with high resolution at sufficient working distances to permit good illumination of samples. The system, which was developed in an in-line configuration, achieves high imaging capacity and exhibits properties that are favorable for micromeasurement. We demonstrate the performance of the system with experiments to determine the displacement of a silicon microcantilever and with investigations of the microscopic resolution capability.

Ferroelectric and electrical behavior of (Na0.5Bi0.5)TiO3 thin films

Sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) of perovskite structure is among the best known lead-free piezoelectric∕ferroelectric that promises a number of applications in sensors and actuators. However, NBT in thin film form has not been properly investigated, although NBT in bulk ceramic form has been widely studied. In this letter, we report the growth of polycrystalline NBT thin films by radio-frequency magnetron sputtering and their ferroelectric behavior. The NBT thin films exhibit a well-defined hysteresis loop, with a remanent polarization of 11.9μC∕cm2 and coercive field of 37.9kV∕cm when measured at room temperature. There is a steady decrease of dielectric constant in the range of 650–470 over the frequency range of 10–105Hz. A change in the controlling mechanism of electrical behavior from the grain interior to the grain boundary is observed for the NBT thin film with increasing temperature. Hopping of oxygen vacancies trapped at the grain boundaries is responsible for the high dielectric l...

A practical guide for the fabrication of microfluidic devices using glass and silicon

This paper describes the main protocols that are used for fabricating microfluidic devices from glass and silicon. Methods for micropatterning glass and silicon are surveyed, and their limitations are discussed. Bonding methods that can be used for joining these materials are summarized and key process parameters are indicated. The paper also outlines techniques for forming electrical connections between microfluidic devices and external circuits. A framework is proposed for the synthesis of a complete glass/silicon device fabrication flow.

Imaging analysis of digital holography

In this study we focus on understanding the system imaging mechanisms given rise to the unique characteristic of discretization in digital holography. Imaging analysis with respect to the system geometries is investigated and the corresponding requirements for reliable holographic imaging are specified. In addition, the imaging capacity of a digital holographic system is analyzed in terms of space-bandwidth product. The impacts due to the discrete features of the CCD sensor that are characterized by the amount of sensitive pixels and the pixel dimension are quantified. The analysis demonstrates the favorable properties of an in-line system arrangement in both the effective field of view and imaging resolution.

Properties of digital holography based on in-line configuration

Digital holography for micromeasurement is an active re- search topic. With respect to the requirement of realizing characteriza- tion of micro-scale structures in microelectromechanical systems with high resolution and accuracy, in-line configuration is studied in this paper as the fundamental structure of a digital holography system. A math- ematical model based on Fourier optics is developed to analyze the digital recording mechanism and properties of the system in comparison with those of the commonly used off-axis arrangement. Theoretical analysis and experimental results demonstrate that in-line configuration is advantageous in enhancing the system performance. Besides the re- laxed requirement of spatial resolution on the CCD sensors and the greater flexibility of the system, higher lateral resolution and lower speckle noise can be achieved.

Aligned carbon nanotubes for through-wafer interconnects

Through-wafer interconnects by aligned carbon nanotube for three-dimensional stack integrated chip packaging applications have been reported in this letter. Two silicon wafers are bonded together by tetra-ethyl-ortho-silicate. The top wafer (100μm thick) with patterned through-holes allows carbon nanotubes to grow vertically from the catalyst layer (Fe) on the bottom wafer. By using thermal chemical vapor deposition technique, the authors have demonstrated the capability of growing aligned carbon nanotube bundles with an average length of 140μm and a diameter of 30μm from the through holes. The resistivity of the bundles is measured to be 0.0097Ωcm by using a nanomanipulator.

A flexible liquid crystal polymer MEMS pressure sensor array for fish-like underwater sensing

In order to perform underwater surveillance, autonomous underwater vehicles (AUVs) require flexible, light-weight, reliable and robust sensing systems that are capable of flow sensing and detecting underwater objects. Underwater animals like fish perform a similar task using an efficient and ubiquitous sensory system called a lateral-line constituting of an array of pressure-gradient sensors. We demonstrate here the development of arrays of polymer microelectromechanical systems (MEMS) pressure sensors which are flexible and can be readily mounted on curved surfaces of AUV bodies. An array of ten sensors with a footprint of 60 (L) mm × 25 (W) mm × 0.4 (H) mm is fabricated using liquid crystal polymer (LCP) as the sensing membrane material. The flow sensing and object detection capabilities of the array are illustrated with proof-of-concept experiments conducted in a water tunnel. The sensors demonstrate a pressure sensitivity of 14.3 μV Pa−1. A high resolution of 25 mm s−1 is achieved in water flow sensing. The sensors can passively sense underwater objects by transducing the pressure variations generated underwater by the movement of objects. The experimental results demonstrate the arrays ability to detect the velocity of underwater objects towed past by with high accuracy, and an average error of only 2.5%.

Microfabricated microneedle with porous tip for drug delivery

This paper presents a novel approach to fabrication of a silicon microneedle array with porous tips. Dry etching technology with SF6/O2 gas by STSs inductively coupled plasma (ICP) etch tool was used to achieve the pyramidal needle structure. A thin silicon nitride layer was deposited after a thick photoresist layer was coated and reflowed at 120 °C. The silicon nitride layer and residual photoresist on the tips of the pyramidal structures were removed using reactive ion etching (RIE). Electrochemical etching in MeCN/HF was carried out to generate porous silicon on the tips of the microneedles. The fabricated microneedle array has potential applications in drug delivery, since the porous tips can be loaded with a high molecular weight drug. Analytic solutions to the critical loadings of the fabricated microneedle structure are also presented. The variations of the square cross-section were expressed as a function of the axial coordinate to analyze the bending normal stress and critical buckling loading. This analytic method can also be used for other microneedle structures with different cross-sections.

Through-wafer electroplated copper interconnect with ultrafine grains and high density of nanotwins

High aspect ratio (∼15) and ultrafine pitch (∼35μm) through-wafer copper interconnection columns were fabricated by aspect-ratio-dependent electroplating. By controlling the process parameters, ultrafine copper grains with nanoscale twins (twin lamellar width ∼20nm) were obtained in the copper columns. Transmission electron microscope reveals that the density of these nanotwins depends on the location along the length of the columns. The highest twin density was achieved at the bottom of the column where the electroplating starts. The presence of higher density of the nanotwins yields significant higher hardness (∼2.4GPa) than that with lower twin density (∼1.8GPa). The electrical conductivity of the electroplated copper (2.2μΩcm) is retained comparable to the pure copper.

A Ruthenium-Based Multimetal-Contact RF MEMS Switch With a Corrugated Diaphragm

This paper presents a ruthenium metal-contact RF microelectromechanical system switch based on a corrugated silicon oxide/silicon nitride diaphragm. The corrugations are designed to substantially reduce the influence of the fabrication-induced stress in the membrane, resulting in a highly insensitive design to process parameter variations. Furthermore, a novel multilayer metal-contact concept, comprising a 50-nm chromium/50-nm ruthenium/500-nm gold/50-nm ruthenium structure, is introduced to improve the contact reliability by having a hard-metal surface of ruthenium without substantial compromise in the contact and transmission-line resistances, which is shown by theoretical analysis of the contact physics and confirmed by measurement results. The contact resistance of the novel metallization stack is investigated for different contact pressures and is compared to pure-gold contacts. The contact reliability is investigated for different dc signal currents. At a measurement current of 1.6 mA, the Ru-Au-Ru contacts have an average lifetime of about 100 million cycles, whereas the Au-Au contacts reach 24 million cycles only. For larger signal currents, the metal contacts have proven to be more robust over the Au-Au contacts by a factor of ten. The measured pull-in voltage is reduced significantly from 61 V for flat diaphragm to 36 V for corrugated diaphragm with the introduction of corrugation. The measured RF isolation with a nominal contact separation of 5 mum is better than -30 dB up to 4 GHz and still -21 dB at 15 GHz, whereas the insertion loss of the fully packaged switch including its transmission line is about -0.7 dB up to 4 GHz and -2.8 dB at 15 GHz.