Porous silicon is a potentially useful substrate for fluorescence and scattering enhancement, with a large surface to volume ratio and thermal stability providing a potentially regenerable host matrix for sensor development. A simple process using XeF2 gas phase etching for creating porous silicon is explained. Moreover, how pores diameter can be controlled reproducibly with commensurate effects upon the silicon reflection and pore distribution is discussed. In previous work with this new system, it was clear that control on pore size and morphology was required and a systematic optimization of process conditions was performed to produce greater consistency of the result. The influence of the duration of the pre-etching processing in HF, concentration of the HF in the pre-etching process, and the XeF2 exposure time during the dry etching on surface morphology, pore size, and optical reflectance is explored.
Porous silicon is a well-known material with interesting properties for a wide variety of applications in electronics,
photonics, medicine, and informatics. We demonstrate fabrication of porous silicon using a dry etching technique. We
demonstrate free standing porous silicon membranes that are only few microns thick. Free standing porous silicon
membranes have the ability to behave as a size-selective permeable membrane by allowing specific sized molecules to
pass through while retaining others. Here, we employ the XeF2 to develop few micrometers thick suspended porous
silicon membranes. The flexibility of XeF2 etching process allows the production of mechanically stable membranes of
different thicknesses. By choosing the appropriate etching parameters and conditions, pore size can be tuned to produce
porous silicon with optically attractive features and desired optical behaviors. The pore size, porosity and thickness of
the various developed ultra-thin free-standing porous silicon membranes were characterized with scanning electron
microscopy and optical transmittance measurements. The fabricated free-standing porous membrane has a typical
transmission spectrum of regular silicon modulated by Fabry-Perot fringes. Porous silicon thin membranes that combine
the properties of a mechanically and chemically stable high surface area matrix with the function of an optical transducer
may find many used in biomedical microdevices.
Mesoporous materials, such as porous silicon and porous polymer gratings (Bragg structures), offer an attractive platform for the encapsulation of chemical and biological recognition elements. These materials include the advantages of high surface to volume ratio, biocompatibility, functionality with various recognition elements, and the ability to modify the material surface/volume properties and porosity. Two porous structures were used for chemical and biological sensing: porous silicon and porous polymer photonic bandgap structures. Specifically, a new dry etching manufacturing technique employing xenon difluoride (XeF2) based etching was used to produce porous silicon Porous silicon continues to be extensively researched for various optical and electronic devices and applications in chemical and biological sensing are abundant. The dry etching technique to manufacture porous silicon offers a simple and efficient alternative to the traditional wet electrochemical etching using hydrofluoric acid. This new porous silicon material was characterized for its pore size and morphology using top and cross-sectional views from scanning electron microscopy. Its optical properties were determined by angular dependence of reflectance measurements. A new class of holographically ordered porous polymer gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. As an alternative structure and fabrication process, porous polymer gratings that include a volatile solvent as the phase separation fluid was fabricated. Porous silicon and porous polymer materials were used as substrates to encapsulate gaseous oxygen (O2) responsive luminophores in their nanostructured pores. These substrate materials behave as optical interference filters that allow efficient and selective detection of the wavelengths of interest in optical sensors.
Porous silicon is an attractive platform for the encapsulation of chemical and biological recognition elements. We
demonstrate fabrication of porous silicon using a dry etching technique. The Xenon Difluoride etching technique allows
selective formation of porous silicon with a standard photoresist layer as mask. We demonstrate free standing 5μm thick
porous silicon films for biological sample filtering. Further, we employ the porous silicon as a substrate for the
immobilization of xerogel thin films that encapsulate specific analyte responsive luminophores in their pores. The porous
silicon behaves as an optical interference filter which allows selective enhancement of the wavelengths of interest.
We report the development of a silicon microelectrode array for brain machine interfaces and neural prosthesis fabricated in a commercial microelectromechanical systems (MEMS) process. We demonstrate high-aspect ratio silicon microelectrodes that reach 6.5 mm in length while having only 10 µm thickness. The fabrication of such elongated neural microelectrodes could lead to the development of cognitive neural prosthetics. Cognitive neural signals are higher level signals that contain information related to the goal of movements such as reaching and grasping and can be recorded from deeper regions of the brain such as the parietal reach region (PRR). We propose a new concept of reinforcing the regions of the electrodes that are more susceptible to breakage to withstand the insertion axial forces, retraction forces, and tension forces of the brain tissue during surgical implantation. We describe the design techniques, detailed analytical models, and simulations to develop reinforced silicon-based elongated neural electrodes. The electrodes are fabricated using the commercial MicraGem process from Micralyne, Inc. The use of a commercial MEMS fabrication process for silicon neural microelectrodes development yields low-cost, mass-producible, and well-defined electrode structures.
Neural microelectrodes are an important component of neural prosthetic systems which assist paralyzed patients by
allowing them to operate computers or robots using their neural activity. These microelectrodes are also used in clinical
settings to localize the locus of seizure initiation in epilepsy or to stimulate sub-cortical structures in patients with
Parkinson's disease. In neural prosthetic systems, implanted microelectrodes record the electrical potential generated by
specific thoughts and relay the signals to algorithms trained to interpret these thoughts. In this paper, we describe novel
elongated multi-site neural electrodes that can record electrical signals and specific neural biomarkers and that can reach
depths greater than 8mm in the sulcus of non-human primates (monkeys). We hypothesize that additional signals
recorded by the multimodal probes will increase the information yield when compared to standard probes that record just
electropotentials. We describe integration of optical biochemical sensors with neural microelectrodes. The sensors are
made using sol-gel derived xerogel thin films that encapsulate specific biomarker responsive luminophores in their
nanostructured pores. The desired neural biomarkers are O2, pH, K+, and Na+ ions. As a prototype, we demonstrate
direct-write patterning to create oxygen-responsive xerogel waveguide structures on the neural microelectrodes. The
recording of neural biomarkers along with electrical activity could help the development of intelligent and more userfriendly
neural prosthesis/brain machine interfaces as well as aid in providing answers to complex brain diseases and
We report the development of a novel methodology for patterning of nanostructured sensory materials using multi-dimensional
microstructured support platforms for optical bioimaging applications. Specifically, the support platforms
are fabricated using direct-write technique and sol-gel derived xerogel thin-films to form the sensor materials. This
creates a simple and versatile method for developing complex 3-D microstructures that have the combined capabilities of
biochemical sensing, microfluidic sample distribution for sensor arrays, and direct integration with Complimentary
Metal-Oxide Semiconductor (CMOS) Integrated Circuits (ICs) used for sensor signal detection and processing. More
importantly, this methodology would enable the development of large-scale arrayed sensing platforms for applications in
cell-culture analysis and tissue imaging. The configuration and fabrication of the proposed microstructures, which
consist of planar ridge and hollow waveguides, will be described in detail. As a prototype implementation, we
demonstrate direct-write ridge waveguide support structures coated with luminophore-doped xerogels that are responsive
to gaseous oxygen (O2) concentration.