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).
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.
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 theoretical and numerical studies of new suspended-silicon-nanowire based
static sensors. These static sensors detect the presence of molecules according to static deflections induced
by the adsorption of molecules. As shown in Fig. 1, the static sensor consists of four suspended silicon nanowires (SiNWs) and one silicon microbeam. Each side of the microbeam includes two SiNWs, instead
of one, to avoid the possible torsion of the microbeam and make the microbeam remain parallel to the
substrate before detection. The microbeam is used as a platform for the adsorption of molecules. The
ultra-high sensitivity of this sensor to mass loading is ensured by the extremely low bending stiffness of the
four supporting SiNWs, while the position and deflection of a microbeam are easily found by a routinely
used instrument due to the relatively large horizontal dimensions of the microbeam. In this work,
theoretical formulation for the sensor deflections under pressure and concentration force is derived and
compared with numerical results. Both theoretical and numerical results are subsequently used to optimize
the design of the static sensors.
Based on mass-loading effect on a microcantilever, there are two approaches for sensing the presence of molecules: dynamic and static methods. In this note, we demonstrate that the two methods actually use the same form of relationships for their sensing purposes, and that if the designed adhesion region of a cantilever is only partially occupied by molecules then neither method can be applied to accurately determine the number of molecules adsorbed.
In this work, an analytical relationship is derived for a doubly-clamped microbeam when it buckles after release from the substrate. In terms of the relationship, compressive residual stress in the doubly-clamped microbeam can be determined according to its buckled shape, allowing one to find the compressive residual stress directly without much experimental effort. This relationship has been used to determine compressive residual stresses in four types of doubly-clamped SiO<sub>2</sub> microbeams. In addition, four methods have been applied to find the elongations of these SiO<sub>2</sub> microbeams, and the corresponding results are compared. Finally, the residual stresses in doubly-clamped SiO<sub>2</sub> microbeams predicted according to the derived relationship are compared with those found in SiO<sub>2</sub> microcantilevers, and the results have a good match.
In this paper, we report an innovative all-polymeric drug-supply device. The micro outlet of the device was ablated through a polymethyl methacrylate (PMMA) layer using a microheater. The size of the ablated micropore was mainly related to the heater temperature profile, and the molten PMMA took the gold heater lines away from the pore area, avoiding possible block of the gold lines to the flow out of the pore. Simulation was conducted to find the temperature profile on the surface of the microheater, and experimental results have a good match with simulation results.
In this work, a new method was developed to increase the stiffness of PDMS (Polydimethylsiloxane) masters using Si plates, aimed at reducing residual deformations of the PDMS masters induced in the molding process. Using this method, both global and local residual deformations in the reinforced PDMS master have been reduced.