A new thinning and trimming approach has been explored to produce silicon nanowires (SiNWs) from silicon
microwires. One-dimensional nanostructures have attracted great attention recently because of their potential
applications as excellent components in micro/nanodevices. SiNWs in particular have received much attention since
silicon is the most widely used material in integrated-circuit and microfabrication processes and has unique mechanical
and electrical properties. However, due to the shortcomings of the existing fabrication approaches, new methods are
needed to produce SiNWs that can not only be massively fabricated but also batch integrated to functional devices. The
developed thinning and trimming approach is believed to be such a method, and would permit precise control of the
structure, size and positions of SiNWs. Furthermore, this method may be used to break through the limitation of
lithography in the sense that silicon features fabricated by any lithographic methods can be further miniaturized using
this approach. Our progress on developing this new thinning and trimming approach is detailed in this paper.
Conducting polymers have received much attention since their discovery in 1977. Applications of conducting polymer
microsystems span from electronic devices to sensors. Traditional sensors had one-to-one correspondence between the
detector and the target. Multiple conducting polymer micropattern arrays on a common substrate, when used for sensing,
can effectively broaden the scope of a sensor. The Intermediate-layer lithography (ILL) technique was developed to
generate multiple conducting polymer micropatterns, of desired dimensions on a common substrate. In this method, the
sizes of the micropatterns can be scaled down effectively. Compared to films, micropatterns exhibited higher sensitivity
at lower analyte concentrations. Also, the response of film sensors was not accurate when the conducting polymer film
was partially covered, indicating that rare concentrations of analytes would be difficult to detect using the conventional
conducting polymer film sensors. In the current work, conducting polymer micropatterns of varying dimensions have
been fabricated using the ILL method and tested for their responses to organic vapors at low concentrations. The
relationship between the surface-to-volume ratios of the micropatterns and their corresponding sensitivities is found for
various target concentrations. The research results would provide insights regarding optimization of the micropattern
sensors for maximizing their sensitivities.
In this work, conducting polymer-based heterojunctions, diodes and capacitors have been generated using an
intermediate-layer lithography (ILL) approach which has been recently developed in our group. Polypyrrole (PPy) and
poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), Poly(methyl methacrylate) (PMMA) and
aluminum were used as component materials in these devices. Compared with Si-based devices, conducting polymerbased
devices have distinctive advantages of low weight and good flexibility, and may potentially replace the
corresponding Si-based devices. A challenge is how to fabricate the conducting polymer-based microsystems. Most
conducting polymers are sensitive to the environment, and their electrical properties tend to deteriorate over time due to
overoxidation (air), moisture, high temperature and chemical alteration. The current fabrication techniques (e.g. lift-off,
dry and wet etching processes) used in lithographic approaches involve ultra-violet, electron-beam, x-ray, gases (e.g.,
oxygen and nitrogen), DI water, and/or chemical solution (e.g. photoresist and acetone), making them improper to
pattern conducting polymers. Since the ILL method does not involve aggressive chemistry in generation of patterns, it
has been employed in this work to fabricate conducting polymer-based microdevices, particularly diodes and capacitors.
In fabrication of the devices, multiple layers of polymers (e.g., PPy and PEDOT) and metals (e.g., Al) are coated on a
PMMA sheet followed by the patterning with the insertion of Si molds. The detailed fabrication procedure and testing
results are given in this paper.
This paper reports our recent fabrication effort in producing suspended-silicon-nanowire based static sensors, which is an
extension to our previous theoretical and numerical studies. The static sensor consists of four suspended silicon dioxide
microwires and one silicon dioxide microplate. Each side of the microplate includes two silicon dioxide microwires,
instead of one, to avoid the possible torsion of the microplate and make the microplate remain parallel to the substrate
before detection. Most of the bridges are curved, instead of being straight, as simulated with the FEA software
previously. Silicon dioxide microbridges were fabricated, and gold/Ni was deposited on the bridge surface. The resulting
deflection was observed with Roughness Step Tester (RST).
The discovery of high conductivity in doped polyacetylene in 1977 (garnering the 2000 Nobel Prize in Chemistry for the three discovering scientists) has attracted considerable interest in the application of polymers as the semiconducting and conducting materials due to their promising potential to replace silicon and metals in building devices. Previous and current efforts in developing conducting polymer microsystems mainly focus on generating a device of a single function. When multiple micropatterns made of different conducting polymers are produced on the same substrate, many microsystems of multiple functions can be envisioned. For example, analogous to the mammalian olfactory system which includes over 1,000 receptor genes in detecting various odors (e.g., beer, soda etc.), a sensor consisting of multiple distinct conducting polymer sensing elements will be capable of detecting a number of analytes simultaneously. However, existing techniques present significant technical challenges of degradation, low throughput, low resolution, depth of field, and/or residual layer in producing conducting polymer microstructures. To circumvent these challenges, an intermediate-layer lithography method developed in our group is used to generate multiple micropatterns made of different, commonly used conducting polymers, Polypyrrole (PPy), Poly(3,4-ethylenedioxy)thiophene (PEDOT) and Polyaniline (PANI). The generated multiple micropatterns are further used in an "electronic nose" to detect water vapor, glucose, toluene and acetone.
A novel approach is proposed in this work to fabricate metallic nano-cantilevers using a one-mask process and deep reactive ion etch (DRIE) technique. Proof-of-concept experiments were conducted, and 40-nm-thick Al and 70-nm-thick Au cantilevers of lengths from 5μm and widths in the range of 200-300nm were fabricated on a silicon substrate. It is found that the silicon underneath the suspended beams had been completely etched. The fabricated metallic nanocantilevers have potential applications in detecting molecules with high sensitivity. Initial stress induced deflection studies have shown these metallic nanocantilevers to be very sensitive to surface modifications.