Robert Kowalczyk

Carbon Nanotube Switches for Communication and Memory Applications

The development of carbon nanotube-based nanoelectromechanical (NEM) switches is described in this work for their potential application in communication and memory systems. Our first NEM structure consists of single walled nanotubes (SWNTs) suspended over shallow trenches in a SiO2 layer, with a Nb pull electrode beneath. DC measurements of these devices show well-defined ON and OFF states as the tube is actuated electrostatically at a few volts. For high frequency applications, electromagnetic modeling of these devices was performed using FEMLAB to calculate the quasi-static capacitance. An equivalent circuit of our switch was developed from which the swept frequency response was simulated up to 100 GHz in the ON and OFF states. A second NEM switch structure, where the tubes are perpendicular to the substrate is also discussed, which is primarily being developed for nonvolatile memory applications. Here, the growth of multi-walled nanotubes (MWNTs) from deep nanopores is described using thermal chemical vapor deposition (CVD) and plasma-enhanced (PE) CVD with Fe and Ni catalyst, respectively, in preparation for the formation of a vertical switch architecture.

Beam splitting mirrors for miniature Fourier transform soft x-ray(FTXR) interferometer

The development of Fourier Transform (FT) spectral techniques in the soft X-ray spectral region has been advocated in the past as a possible route to constructing a bench-top size spectral imager with high spatial and spectral resolution. The crux of the imager is a soft X-ray interferometer. Auxiliary subsystems include a wide-band soft X-ray source, focusing optics and detection systems. When tuned over a sufficiently large range of path delays, the interferometer will sinusoidally modulate the source spectrum centered at the core wavelength of interest, the spectrum illuminates a target, the reflected signal is imaged onto a CCD, and data acquired for different frames is converted to spectra in software by using FT methods similar to those used in IR spectrometry producing spectral image per each pixel. The use of shorter wavelengths results in dramatic increase in imaging resolution, the modulation across the beam width results in highly efficient use of the beam spectral content, facilitating construction of a bench-top instrument. With the predicted <0.1eV spectral and <100 nm spatial resolution, the imager would be able to map core-level shift spectra for elements such as Carbon, which can be used as a chemical compound fingerprint and imaging intracellular structures. We report on our progress in the development of a Fourier Transform X-ray (FTXR) interferometer. The enabling technology is X-ray beam splitting mirrors. The mirrors are not available commercially; multi layers of quarter-wave films (used in IR and visible) are not suitable, and several efforts by other researchers who used parallel slits met only a very limited success. In contrast, our beam splitters use thin (about 200 nm) SiN membranes perforated with a large number of very small holes prepared in our micro-fabrication laboratory at JPL. Precise control of surface roughness and high planarity are needed to achieve the requisite wave coherency. The beam splitters prepared-to-date had surface RMS and planarity better that <0.3 nm over a 0.45 mm x 1.4 mm area, meeting requirements for spectral imaging at 100eV. Efforts to improve the mirror flatness to a level required for core-level shifts of Carbon are under way.

Vacuum microelectronics applications using carbon nanotube cathodes

We will present the recent advances in carbon nanotube bundle array based field emission electron source development. These cathodes are being applied for developing new vacuum microelectronic devices. Some application issues, cathode life time, current density influencing factors, and a novel electrode integration technique will be described.

High-Throughput Top-Down and Bottom-Up Processes for Forming Single-Nanotube Based Architectures for 3D Electronics

We have developed manufacturable approaches to form single, vertically aligned carbon nanotubes, where the tubes are centered precisely, and placed within a few hundred nm of 1-1.5 m deep trenches. These wafer-scale approaches were enabled by chemically amplified resists and inductively coupled Cryo-etchers for forming the 3D nanoscale architectures. The tube growth was performed using dc plasma-enhanced chemical vapor deposition (PECVD), and the materials used for the pre-fabricated 3D architectures were chemically and structurally compatible with the high temperature (700 °C) PECVD synthesis of our tubes, in an ammonia and acetylene ambient. Tube characteristics were also engineered to some extent, by adjusting growth parameters, such as Ni catalyst thickness, pressure and plasma power during growth. Such scalable, high throughput top-down fabrication techniques, combined with bottom-up tube synthesis, should accelerate the development of PECVD tubes for applications such as interconnects, nano-electromechanical (NEMS), sensors or 3D electronics in general.