Micro-electrical Systems Research Articles

Electroless Deposition of CoMoP and CoMoB Alloy Thin Films

CoMoP and CoMoB alloys was produced using a simple modification of the commonly used CoP bath. The proposed process is similar to that of electroless CoWP, which have been demonstrated from an electrolyte with sodium tungstate (Na2WO4) or tungsten phosphoric acid (H3[P(W3O10)4]) as a source of the W-ions. In this paper we demonstrate a Co-Mo-P (or B) electroless deposition bath using either cobalt-sulfate and cobalt-dichloride bath under basic conditions (pH~9 for the phosphorous alloy and 12-14 for the boron alloy) using sodium hypophosphite or sodium borohydride as the reducing agents. The refractory metal was introduced to the solutions by adding molybdate ions. The material and electrical properties of the obtained films were characterized and presented here. The deposition process presented here are compatible with microelectronics microfabrication process; thus they can be applied for microelectronics, micro electrical systems (MEMS) or packaging; however their barrier and capping properties for copper metallization are yet to be determined.

Thermo-optical characterization of fluorescent rhodamine B based temperature-sensitive nanosensors using a CMOS MEMS micro-hotplate

A custom designed microelectromechanical systems (MEMS) micro-hotplate, capable of operating at high temperatures (up to 700°C), was used to thermo-optically characterize fluorescent temperature-sensitive nanosensors. The nanosensors, 550nm in diameter, are composed of temperature-sensitive rhodamine B (RhB) fluorophore which was conjugated to an inert silica sol–gel matrix. Temperature-sensitive nanosensors were dispersed and dried across the surface of the MEMS micro-hotplate, which was mounted in the slide holder of a fluorescence confocal microscope. Through electrical control of the MEMS micro-hotplate, temperature induced changes in fluorescence intensity of the nanosensors was measured over a wide temperature range. The fluorescence response of all nanosensors dispersed across the surface of the MEMS device was found to decrease in an exponential manner by 94%, when the temperature was increased from 25°C to 145°C. The fluorescence response of all dispersed nanosensors across the whole surface of the MEMS device and individual nanosensors, using line profile analysis, were not statistically different (p<0.05). The MEMS device used for this study could prove to be a reliable, low cost, low power and high temperature micro-hotplate for the thermo-optical characterisation of sub-micron sized particles. The temperature-sensitive nanosensors could find potential application in the measurement of temperature in biological and micro-electrical systems.

Process for the fabrication of complex three-dimensional microcoils in fused silica

The creation of complex three-dimensional (3D) microcoils has attracted significant attention from both scientific and applied research communities. However, it still remains challenging to build 3D microcoils with arbitrary configurations using conventional planar lithographic fabrication methods. This Letter presents a new facile method based on an improved femtosecond laser wet etch technology and metal microsolidifying process for the fabrication of on-chip complex 3D microcoils inside fused silica. The diameter of the microcoils is about 30 μm, and the effective length of the microchannel is about 13 mm. The aspect ratio of the microcoils can be larger than 400:1, and the microchannel exhibiting good uniformity and smoothness also has good flowability for high-viscosity conductive gallium metal. Based on this approach, we fabricated complex microcoils such as U-shaped and O-shaped microcoils that can be easily integrated into a "lab on a chip" platform or microelectric system inside fused-silica substrate.

Neural Tissue Engineering and Biohybridized Microsystems for Neurobiological Investigation In Vitro (Part 1)

Advances in neural tissue engineering have resulted in the development and implementation of three-dimensional (3-D) neural cellular constructs, which may serve as neurofidelic in vitro investigational platforms. In addition, interfacing these 3-D cellular constructs with micro-fluidic and/or micro-electrical systems has created biohybridized platforms, providing unprecedented 3-D microenvironmental control and allowing noninvasive probing and manipulation of cultured neural cells. Cells in the brain interact within a complex, multicellular environment with tightly coupled 3-D cell-cell/cell-extracellular matrix (ECM) interactions; yet most in vitro models utilize planar systems lacking in vivo-like ECM. As such, neural cultures with cells distributed throughout a thick (> 500 microm), bioactive extracellular matrix may provide a more physiologically relevant setting to study neurobiological phenomena than traditional planar cultures. This review presents an overview of 2-D versus 3-D culture models and the state of the art in 3-D neural cell-culture systems. We then detail our efforts to engineer a range of 3-D neural cellular constructs by systematically varying parameters such as cell composition, cell density, matrix constituents, and mass transport. The ramifications on neural cell survival, function, and network formation based on these parameters are specifically addressed. These 3-D neural cellular constructs may serve as powerful investigational platforms for the study of basic neurobiology, network neurophysiology, injury/disease mechanisms, pharmacological screening, or test-beds for cell replacement therapies. Furthermore, while survival and growth of neural cells within 3-D constructs poses many challenges, optimizing in vitro constructs prior to in vivo implementation offers a sound bioengineering design approach.

Theoretical and experimental study on the kerf profile of the laser micro-cutting NiTishape memory alloy using 355 nm Nd:YAG

The NiTi shape memory alloy is attracting more and more attention inthe fabrication of micro-electrical systems (MEMS) components because ofits special shape memory effect and superelastic properties, especially inmicroactuator and microsensor applications. Laser cutting is one of the methods ofmicro-machining the bulk NiTi alloy. In this study, thin NiTi sheets with a thickness of350 µm were micro-cut using a 355 nm Nd:YAG laser. A qualitative theoretical analysis andexperimental investigations of the process parameters on the kerf profile and cuttingquality were performed. The results show that the kerf profile and cutting quality aresignificantly influenced by the process parameters, such as the single pulse energy, scanspeed, frequency, pass number and beam offset, with the single pulse energy and passnumber having the most significant effects. Based on our analysis, the process parametersare optimized. Debris-free kerf with narrow width () and small taper () is obtained.

A new type of low power thermoelectric micro-generator fabricated by nanowire array thermoelectric material

A new type of thermoelectric micro-generator, which is composed of n-type and p-type Bi 2Te 3 nanowire array thermoelectric materials, is designed to be energy source for miniaturized solid-state devices such as MEMS, micro-electrical system and even “system on a chip”. The nanowire arrays are fabricated by electrochemical deposition of Bi 2Te 3 into the nano-pores of alumina template. The measurements showed that the Seebeck coefficient α of p-type and n-type Bi 2Te 3 nanowire arrays is about 260 and −188 μV/K separately with the nanowire diameter of about 50 nm at 307 K. The thermoelectric micro-generator is designed to possess a film like configuration and a laminar structure as C layer/B layer/A layer/B layer/C layer. The A layer is thermoelectric material layer consisting of a great amount of n-type and p-type nanowire micro-zones. Two B layers are electric conductive layers which realize the series electric connection of n-type and p-type micro-zones in A layer. The other two C layers are thermal conductive layers. By the use of IC technology, the micro-generator can obtain a high voltage output, and its thickness is less than 200 μm. The unique laminar structure makes thermo-electricity conversion more effective. An important aspect that distinguishes our device from the conventional one is that thermoelectric nanowire arrays are firstly used to fabricate thermoelectric micro-generator.