Reginald C. Farrow

Directed self-assembly of individual vertically aligned carbon nanotubes

The deposition of high-aspect-ratio particles such as carbon nanotubes may be done in sub-100-nm windows in insulating thin films over metal using electrophoresis. Surface charge on the insulator causes the windows to become nanoscopic electrostatic lenses. Under certain conditions only one nanotube will be deposited at the base of a window. Finite element analysis shows that the number of deposited nanotubes is controlled by the electric field and the geometry of the windows and nanotubes. This discovery enables the process integration of carbon-based electronics with more traditional technologies such as complementary metal oxide semiconductor using the current generation of lithography and process technology. Devices such as vertical field effect transistors and interconnected nanoprobe arrays may now be fabricated in the metal levels to facilitate three-dimensional polylithic circuit architectures.

An Angstrom-sensitive, differential MEMS capacitor for monitoring the milliliter dynamics of fluids

A device, with MEMS sensors at its core, has been fabricated and tested for measuring low fluid pressure and slow flow rates. The motivation was to measure clinically relevant ranges of slow-moving fluids in living systems, such as the cerebrospinal fluid in the brain. For potential clinical utility, the device can be read transcutaneously by inductive coupling to MEMS capacitive sensors in circuits with resonance frequencies in the MHz range. Signal shifts for flow rates in the range of 0-42 mL/h and differential pressure levels between 0.1 and 2 kPa have been measured, because the sensitivity in the capacitance gap measurement is about 1 Å. The sensors have been used successfully to monitor simulated cerebrospinal fluid dynamics. The device does not utilize any internal power, since it is powered externally via the inductive coupling.

Scalable nano-bioprobes with sub-cellular resolution for cell detection.

Here we present a carbon nanotube based device to noninvasively and quickly detect mobile single cells with the potential to maintain a high degree of spatial resolution. The device utilizes standard complementary metal oxide semiconductor (CMOS) technologies for fabrication, allowing it to be easily scalable (down to a few nanometers). Nanotubes are deposited using electrophoresis after fabrication in order to maintain CMOS compatibility. The devices are spaced by 6 μm which is the same size or smaller than a single cell. To demonstrate its capability to detect cells, we performed impedance spectroscopy on mobile human embryonic kidney (HEK) cells, neurons cells from mice, and yeast cells (S. pombe). Measurements were performed with and without cells and with and without nanotubes. Nanotubes were found to be crucial to successfully detect the presence of cells. The devices are also able to distinguish between cells with different characteristics.

Evidence of an application of a variable MEMS capacitive sensor for detecting shunt occlusions

A sensor was tested subdural and in vitro, simulating a supine infant with a ventricular-peritoneal shunt and controlled occlusions. The variable MEMS capacitive device is able to detect and forecast blockages, similar to early detection procedures in cancer patients. For example, with gradual occlusion development over a year, the method forecasts a danger over one month ahead of blockage. The method also distinguishes between ventricular and peritoneal occlusions. Because the sensor provides quantitative data on the dynamics of the cerebrospinal fluid, it can help test new therapies and work toward understanding hydrocephalus as well as idiopathic normal pressure hydrocephalus. The sensor appears to be a substantial advance in treating brain injuries treated with shunts and has the potential to bring significant impact in a clinical setting.

Microfabricated implantable pressure sensor for flow measurement

A RF wireless capacitive pressure sensor is developed. The sensor has integrated inductor with the pressure sensitive capacitor as LC circuit. The resonant frequency of the sensor changes as the capacitance changes with applied pressure. The sensor uses LPCVD silicon nitride as sensitive membrane and the residual stress of the membrane has been measure as 139MPa. The sensor has size of 10 mm × 4 mm × 0.5 um. The sensor presents a pressure sensitivity of 1.65 MHz/cmH2O in pressure range of 0-20 cmH2O. The deflection of different shape of membranes is discussed. The deflection of square membrane is 130% to circular membrane under same applied pressure.

Mapping the dispersion of water wave channels

Large classes of electronic, photonic, and acoustic crystals and quasi-crystals have been predicted to support topological wave-modes. Some of these modes are stabilized by certain symmetries but others occur as pure wave phenomena, hence they can be observed in many other media that support wave propagation. Surface water-waves are mechanical in nature but very different from the elastic waves, hence they can provide a new platform for studying topological wave-modes. Motivated by this perspective, we report theoretical and experimental characterizations of water-wave crystals obtained by periodic patterning of the water surface. In particular, we demonstrate the band structure of the spectra and existence of spectral gaps.

Microfabricated implantable flow sensor for medical applications

A RF wireless capacitive flow sensor is developed. The sensor has integrated inductor with the flow sensitive capacitors as LC circuit. The resonant frequency of the sensor changes as the capacitance changes with applied flow. The sensor uses LPCVD silicon nitride as sensitive membrane and the residual stress of the membrane has been measure as 139 MPa. The sensor has size of 10 mm × 4 mm × 0.5 μm. The sensor integrated two pressure sensors together and designed related to flow 5-20ml/hour. The deflection of different shape of membranes and the parameters of flow sensor sensitivity are discussed. The deflection of square membrane is 130% to circular membrane under same applied pressure.