Dean M. Aslam

Climbing the walls [robots]

Presents two underactuated kinematic designs for miniature climbing robots. They use suction. The underactuation is to save weight.

A Novel Diamond Microprobe for Neuro-Chemical and -Electrical Recording in Neural Prosthesis

This paper describes the design, microfabrication, and testing of a novel polycrystalline-diamond (poly-C)-based microprobe for possible applications in neural prosthesis. The probe utilizes undoped poly-C with a resistivity on the order of 105 Omega middot cm as a supporting material, which has a Youngs modulus in the range of 400-1000 GPa and is biocompatible. Boron-doped poly-C with a resistivity on the order of 10-3 Omega middot cm is used as an electrode material, which provides a chemically stable surface for both chemical and electrical detections in neural studies. The probe has eight poly-C electrode sites with diameters ranging from 2 to 150 mum; the electrode capacitance is approximately 87 muF/cm2. The measured water potential window of the poly-C electrode spans across negative and positive electrode potentials and typically has a total value of 2.2 V in 1 M KCl. The smallest detectable concentration of norepinephrine (a neurotransmitter) was on the order of 10 nM. The poly-C probe has also been successfully implanted in the auditory cortex area of a guinea pig brain for in vivo neural studies. The recorded signal amplitude was 30-40 muV and had a duration of 1 ms.

Ultra-high sensitivity intra-grain poly-diamond piezoresistors

Abstract Chemical vapor deposited (CVD) polycrystalline diamond is inexpensive and can become a commercially viable piezoresistive sensor material if its typical gauge factor (GF) exceeds that of crystalline Si and SiC. In this paper, a study of GF of B-doped polycrystalline diamond film leads to an intra-grain GF above 4000, which is comparable to GF of single crystal p-type diamond. This result, reported for the first time, shows that large-grain (50–80 μm) CVD diamond can be used to build inexpensive ultra-high sensitivity piezoresistive sensors.

High-Performance Polycrystalline Diamond Micro- and Nanoresonators

Cantilever type MEMS resonators were fabricated using boron-doped (~5 times 1019 cm-3) and undoped polycrystalline diamond (poly-C) films that were grown at 600degC or 780degC. The resonator dimensions ranged from 500 mum long, 10 mum wide, and 0.7 mum thick to 40 mum long, 100 nm wide, and 0.6 mum thick. Resonance frequencies and quality factors Qs were measured in vacuum, 10 5 torr, over the temperature range of 23degC-400degC. The measured values of the temperature coefficient of the resonance frequency were in the range of -7.2- -25.6 ppm. degC-1 and seemed to be related to changes in the Youngs modulus with temperature. Undoped poly-C cantilevers exhibit Qs as high as 116 000, the highest value reported for a cantilever resonator fabricated from a polycrystalline film. A thermally activated relaxation process seems to limit the measured Q -values for the highly doped poly-C samples.

Design, implementation, and evaluation of an under-actuated miniature biped climbing robot

The design, implementation, and evaluation of a miniature biped robot for urban reconnaissance are presented. Design specifications for mobility, space requirement weight, sensing, and control are defined. A revolute hip joint is selected based on its enhanced mobility and capability to function in reasonably confined spaces. Small size dictates minimal weight, which is achieved by an under actuated joint structure, providing steering at only one foot, minimizing sensors, and structural optimization. The smart robotic foot supports the robot on a variety of smooth surfaces and provides feedback when a firm grip is established. Adaptable control strategies and dithering are implemented in lieu of minimal sensors and uncertainty created by backlash, gravity, and compliance in the suction feet. The robot is evaluated while performing tasks on surfaces with a variety of inclinations.

The fabrication of all-diamond packaging panels with built-in interconnects for wireless integrated microsystems

To explore polycrystalline diamond (poly-C) as a packaging material for wireless integrated microsystems (WIMS), a new fabrication technology has been developed to fabricate thick WIMS packaging panels with built-in interconnects. An ultrafast poly-C growth technique, used in this study, involves electrophoresis seeding and filling of dry-etched Si channels by undoped poly-C followed by removal of Si. A second layer of highly B-doped poly-C, which acts as a built-in interconnect, is deposited on the backside of undoped poly-C layer. The lowest resistivity values demonstrated on control samples are in the range from 0.003 to 0.31 /spl Omega/-cm. The results show that, by increasing the poly-C growth areas through the use of 2-/spl mu/m-wide Si channels, the poly-C growth time can be reduced by a factor in the range from 2.75 to 10.5 depending upon the aspect ratio of Si channels. The poly-C packaging technology, which is expected to provide new structures/concepts in MEMS/WIMS packaging, is being reported for the first time.

Technology of polycrystalline diamond thin films for microsystems applications

Large area and uniform polycrystalline diamond (poly-C) thin films, with a thickness of approximately 1μm, were grown and patterned on 4in. oxidized Si wafers using IC compatible processes for microsystems applications. Uniform and reproducible seeding with a density of 2×1010∕cm2 was achieved by spinning diamond powder loaded water on 4in. wafers. Gas mixture of 1.5% methane in hydrogen was used in MPCVD system for diamond film growth with optimized pressure and microwave power. Thickness variation of less than 20% was achieved on the 4in. area using 43Torr pressure and 2.8kW microwave power. Electron cyclotron resonance (ECR)-assisted microwave plasma reactive ion etch was carried out using SF6∕O2∕Ar gases to pattern the diamond films with an etch rate around 80nm∕min and less than 10% variation in etch rate over a 4in. area.

Fabrication of 2-μm wide poly-crystalline diamond channels using silicon molds for micro-fluidic applications

Abstract The deposition of poly-crystalline diamond (poly-C) in narrow silicon channels has been accomplished, resulting in narrow freestanding diamond channels. The channels were seeded using a combination of ultrasonic stirring and electrophoresis in a diamond/isopropanol solution. These channels have openings with thicknesses as low as ∼2 μm. The use of such diamond channels for picoliter chemical transfer or storage is proposed. Narrow micro-fluidic channels made completely of poly-C have been fabricated for the first time.

Synthesis of high-density carbon nanotube films by microwave plasma chemical vapor deposition

Abstract Nanotubes with diameters ranging from 20 to 400 nm and densities in the range of 108–109 cm−2, produced on metal-coated silicon by microwave plasma chemical vapor deposition, show various shapes depending upon: (i) growth conditions; and (ii) pre- or post-growth treatment of the samples. Presence of nitrogen in the growth or pre-growth atmosphere increases the density and vertical growth rate of nanotubes. The growth rate on an iron-coated substrate is higher than on a nickel-coated substrate. A cleaning procedure, consisting of ultrasonic treatment of nanotubes in methanol, is demonstrated.

Polycrystalline-Diamond MEMS Biosensors Including Neural Microelectrode-Arrays

Diamond is a material of interest due to its unique combination of properties, including its chemical inertness and biocompatibility. Polycrystalline diamond (poly-C) has been used in experimental biosensors that utilize electrochemical methods and antigen-antibody binding for the detection of biological molecules. Boron-doped poly-C electrodes have been found to be very advantageous for electrochemical applications due to their large potential window, low background current and noise, and low detection limits (as low as 500 fM). The biocompatibility of poly-C is found to be comparable, or superior to, other materials commonly used for implants, such as titanium and 316 stainless steel. We have developed a diamond-based, neural microelectrode-array (MEA), due to the desirability of poly-C as a biosensor. These diamond probes have been used for in vivo electrical recording and in vitro electrochemical detection. Poly-C electrodes have been used for electrical recording of neural activity. In vitro studies indicate that the diamond probe can detect norepinephrine at a 5 nM level. We propose a combination of diamond micro-machining and surface functionalization for manufacturing diamond pathogen-microsensors.