Low resistance is an important requirement for microcoils which act as a signal receiver to ensure low thermal noise during signal detection. High-aspect ratio (HAR) planar microcoils entrenched in blind silicon trenches have features that make them more attractive than their traditional counterparts employing electroplating through a patterned thick polymer or achieved through silicon vias. However, challenges met in fabrication of such coils have not been discussed in detail until now. This paper reports the realization of such HAR microcoils embedded in Si blind trenches, fabricated with a single lithography step by first etching blind trenches in the silicon substrate with an aspect ratio of almost 3∶1 and then filling them up using copper electroplating. The electroplating was followed by chemical wet etching as a faster way of removing excess copper than traditional chemical mechanical polishing. Electrical resistance was further reduced by annealing the microcoils. The process steps and challenges faced in the realization of such structures are reported here followed by their electrical characterization. The obtained electrical resistances are then compared with those of other similar microcoils embedded in blind vias.
A detailed characterization of PECVD to produce low stress amorphous silicon carbide (α-SiC) layers at high deposition
rate has been done and the biomedical applications of α-SiC layers are reported in this paper. By investigating different
working principles in high-frequency mode (13.56MHz) and in low frequency mode (380KHz), it is found that
deposition in high-frequency mode can achieve low stress layers at high deposition rates due to the structural rearrangement
from high HF power, rather than the ion bombardment effect from high LF power which results in high
compressive stress for α-SiC layers. Furthermore, the effects of deposition temperature, pressure and reactant gas ratios
are also investigated and then an optimal process is achieved to produce low stress α-SiC layers with high deposition
rates.
To characterize the PECVD α-SiC layers from optimized process, a series of wet etching experiments in KOH and HF
solutions have been completed. The very low etching rates of PECVD α-SiC layers in these two solutions show the good
chemical inertness and suitability for masking layers in micromachining. Moreover, cell culture tests by seeding
fibroblast NIH3T3 cells on the monocrystalline SiC, low-stress PECVD α-SiC released membranes and non-released
PECVD α-SiC films on silicon substrates have been done to check the feasibility of PECVD α-SiC layers as substrate
materials for biomedical applications. The results indicate that PECVD α-SiC layers are good for cell culturing,
especially after treated in NH4F.
The paper presents a novel microfluidic device for identification and characterization of cells in suspensions using impedance spectroscopy. The device consists of two glass wafers: a bottom wafer comprising a microfluidic channel with two electrodes added for impedance measurement, and a top glass wafer in which inlets and outlets are realized. The fact that the device is glass-based provides a few key advantages: reduced influence from parasitic components during measurements (due to the good isolation properties of the substrate), optical transparency and hydrophilic surface of the microfluidic channel. The latter feature is especially important as it enables sample suction due to capillarity forces only. Thus, no external pumping is required and only a small volume sample suffices for the measurement.
The fabrication process of this device consists of three major steps. First, via-holes and inlet/outlet holes are executed in the top glass wafer by wet etching in a 49% HF solution using a low stress amorphous silicon/silicon carbide/photoresist mask. Second, the microfluidic channel is etched into the bottom wafer and Ti/Pt electrodes are then patterned on top of it using a spray coating-based lithography. The last processing step is bonding together the top and bottom glass wafers by employing a very thin adhesive intermediate layer (SU8). This adhesive layer was applied selectively only on the bottom die, from a Teflon cylinder, using a contact imprinting method.
Finally, fabricated devices were successfully tested using DI water, phosphate buffer saline (PBS), and various types of both dead cells and living cells resuspended in PBS. Clear differences between dead and live cells have been observed. The impedance measurements were carried out in the frequency range 5 kHz to 10 MHz. The measured magnitude and phase were studied using different types of cells in Dulbecco's Minimal Essential medium (DMEM). The obtained impedance spectra revealed the characteristic spectra signature for each type of cell.
This paper explores the basic notions and limitations which should be considered in the design of an integrated spectrometer implemented using microelectronic processing. The infrared (IR) range is the main focus of attention, but the design rules are meant to be very general and more wavelength domains will have to be taken into consideration. Some general principles and design rules necessary to generate the desired spectral dispersion of a certain wavelength range will be presented, by means of which an integrated spectrometer could be designed/optimized.
The basic aim of this work is to obtain optical detectors with a spectral response programmable by design using the combined response of polysilicon and monocrystalline silicon photodiodes. Such an approach is needed in order to obtain a color sensor with improved flexibility and control of its characteristic parameters. In order to achieve this aim, the potential of different multilayer thin film light detectors has been evaluated. The results show that polysilicon diodes can be realized and used as light detectors and a simple test structure has been fabricated in order to demonstrate the possiblity of implementing thin film color detecting structures.
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