BMEplanet

BMEplanet - a consortium of more than 260 organizations spanning 43 countries on six continents - is launching a unique Web 2.0 collaboration suite to accelerate education, research, and innovation in bioengineering. This interactive suite, comprising an internship bank, collaborative project workspaces, and an "idea box," is freely available as a service to the community. BMEplanet is funded by the National Science Foundation (NSF) and the Ewing Marion Kauffman Foundation, the world's largest foundation devoted to entrepreneurship.     

Electromagnetic fast firing for ultrashallow junction formation

The creation of low resistivity, ultrashallow source/drain regions in MOS device structures requires rapid thermal processing (RTP) techniques that restrict diffusion and activate a significant percentage of the implanted dopant species. While current heating techniques depend upon illumination based heating, a new technology, electromagnetic induction heating (EMIH), achieves a rapid heating of the silicon by coupling electromagnetic radiation directly into the silicon wafer. Heating rates of 125/spl deg/C/s to temperatures in excess of 1050/spl deg/C have been achieved for 75- and 100-mm-diameter wafers at input powers of 1000 and 1300 W, respectively. These ramp rates are suitable for ultrashallow junction formation, and junctions shallower than 30 nm with sheet resistances lower than 600 /spl Omega//square have been achieved. This paper details the application of electromagnetic heating using radiation in the microwave, 2450 MHz, frequency regime. Experimental results, comparing microwave annealed implants to the well documented SEMATECH requirements, and simulations, utilizing a coupled electromagnetic-thermal computer model, of the heating process are discussed.     

A temperature-dithering closed-loop interface circuit for a scanning thermal microscopy system

This work presents an interface circuit for low-frequency dithering measurements of resistor-based transducers. It is demonstrated in the context of a polyimide-shank scanning thermal microscopy probe which provides high thermal sensitivity and spatial resolution, but has a low bandwidth from both mechanical and thermal perspectives. These pose challenges in temperature dithering and control, as well as noise immunity. The circuit includes a proportional-integral controller and a demodulator, along with appropriate amplifier and filter blocks. It keeps the average temperature of the probe tip constant while synchronously detecting variations in the second harmonic of the modulated signal as the tip is scanned across the sample surface. Strategic choices in the circuit architecture and topology are evaluated, and the overall system including the sensor and the circuit is simulated. Measurements of the implemented system show that a signal-to-noise ratio (SNR) of 15.7 is achieved while scanning a photoresist sample of 218 nm thickness on a silicon substrate, and that the detection limit for variations in thermal conductance is <3 pW/K.     

An experimental study of the contact mode AFM scanning capability of polyimide cantilever probes

This paper presents a preliminary exploration of high-speed contact mode performed with a polyimide probe. The probe is batch micromachined by a lithographic manufacturing process. It offers a spring constant of <0.1N/m, a resonance frequency of about 50k Hz, and a tip diameter of 50-100 nm. The probe is particularly suitable for scanning soft specimens such as biological and polymeric samples. Topographical contact mode imaging at high scanning rates of 48 Hz (1.47 mm/s) has been demonstrated, detecting features <100 nm over a 15 microm scan, yielding >7 bit resolution at 48 Hz. Scanning rates of 16 Hz (0.5mm/s) have been demonstrated for lateral force imaging with spatial resolution of 100 nm over a 15 microm scan, which translates into >7 bit resolution at 16 Hz. These results suggest that the probe can be used in high throughput applications.     

Joining of SiC,alumina, and mullite by the Refractory Metal—Wrap pressure-less process

The aim of this work was to discuss the suitability of the joining process called “RM-Wrap” (RM = Refractory Metals, ie, Mo, Nb, Ta, Zr) as a pressure-less and tailorable technique to join several different ceramics such as SiC, alumina, and mullite (3Al₂O₃.2SiO₂). In the RM-Wrap joining technique the refractory metal foil is used as a wrap containing one or more silicon foils. It is performed at 1450°C, under flowing argon, and the resulting joining materials are in situ formed composites made of refractory metal disilicides (MoSi₂, NbSi₂, TaSi₂, or ZrSi₂) embedded in a silicon-rich matrix; their coefficient of thermal expansion has been calculated and the Laser Flash Method was used to measure the thermal diffusivity of one of them (MoSi₂/Si) in 25°C-1000°C range, then to calculate its thermal conductivity. All the obtained joints are uniform, continuous, and crack free. Some preliminary oxidation tests were carried out on all joints at 1100°C, 6 hours in air, giving unchanged morphology of the interface and the joining materials itself; the joint strength of RM-Wrap joined SiC was measured at room temperature using three different mechanical tests: (a) single lap (SL), (b) single lap off-set (SLO) and (c) torsion on hourglass-shaped samples (THG) (on Mo-wrap joined SiC).     

Pressure‐less joining of C/SiC and SiC/SiC by a MoSi2/Si composite

A MoSi₂/Si composite obtained in situ by reaction of silicon and molybdenum at 1450°C in Ar flow is proposed as pressure‐less joining material for C/SiC and SiC/SiC composites. A new “Mo‐wrap” technique was developed to form the joining material and to control silicon infiltration in porous composites. MoSi₂/Si composite joining material infiltration inside coated and uncoated C/SiC and SiC/SiC composites, as well as its microstructure and interfacial reactions were studied. Preliminary mechanical strength of joints was tested at room temperature and after aging at service temperatures, resulting in interlaminar failure of the composites in most cases.     

A Si/Glass Bulk-Micromachined Cryogenic Heat Exchanger for High Heat Loads: Fabrication, Test, and Application Results

This paper reports on a micromachined Si/glass stack recuperative heat exchanger with in situ temperature sensors. Numerous high-conductivity silicon plates with integrated platinum resistance temperature detectors (Pt RTDs) are stacked, alternating with low-conductivity Pyrex spacers. The device has a $1 times 1hbox{-cm}^{2}$ footprint and a length of up to 3.5 cm. It is intended for use in Joule–Thomson (J–T) coolers and can sustain pressure exceeding 1 MPa. Tests at cold-end inlet temperatures of 237 K–252 K show that the heat exchanger effectiveness is 0.9 with 0.039-g/s helium mass flow rate. The integrated Pt RTDs present a linear response of 0.26%–0.30%/K over an operational range of 205 K–296 K but remain usable at lower temperatures. In self-cooling tests with ethane as the working fluid, a J–T system with the heat exchanger drops 76.1 K below the inlet temperature, achieving 218.7 K for a pressure of 835.8 kPa. The system reaches 200 K in transient state; further cooling is limited by impurities that freeze within the flow stream. In J–T self-cooling tests with an external heat load, the system reaches 239 K while providing 1 W of cooling. In all cases, there is an additional parasitic heat load estimated at 300–500 mW.$ hfill$[2009-0093]      

Surface micromachined polyimide scanning thermocouple probes

This paper describes micromachined scanning thermocouple probes that exploit the low thermal conductivity and the high mechanical flexibility of polyimide as a structural material. They are surface micromachined using a low-temperature six-mask process suitable for appending to a CMOS fabrication sequence. The probes are 200-1000-μm long, 40-120-μm wide, and of varying thickness. They are assembled by a flip-over approach that eliminates the need for dissolving the substrate wafer or removing the probe from it. Temperature sensing is provided by thin-film Ni/W or chromel/alumel thermopiles embedded in the polyimide, which provide Seebeck coefficients of 22.5 and 37.5 μV/K per junction, respectively. Modeling results indicate that the low thermal conductivity of polyimide causes the temperature drop along the probe length to be much higher than with other candidate materials such as Si or SiO₂, which contributes to improved thermal isolation of the sample and higher temperature sensitivity of the probe. However, the response time of the probe is compromised, and the measured -3 dB bandwidth of the probes is ≈500 Hz. A sample scan is presented     

Bent-beam electrothermal actuators-Part II: Linear and rotarymicroengines

For Part I see L. Que, J.S. Park and Y.B. Gianchandani, ibid., vol.10, pp.247-54 (2001). This paper reports on the use of bent-beam electrothermal actuators for the purpose of generating rotary and long-throw rectilinear displacements. The rotary displacements are achieved by orthogonally arranged pairs of cascaded actuators that are used to rotate a gear. Devices were fabricated using electroplated Ni, p ⁺⁺ Si, and polysilicon as structural materials. Displacements of 20-30 μm with loading forces >150 μN at actuation voltages <12 V and power dissipation <300 mW could be achieved in the orthogonally arranged actuator pairs. A design that occupies <1 mm ² area is presented. Long-throw rectilinear displacements were achieved by inchworm mechanisms in which pairs of opposing actuators grip and shift a central shank that is cantilevered on a flexible suspension. A passive lock holds the displaced shank between pushes and when the power is off. This arrangement permits large output forces to be developed at large displacements, and requires zero standby power. Several designs were fabricated using electroplated Ni as the structural material. Forces >200 μN at displacements >100 μm were measured     

Microfluidic electrodischarge devices with integrated dispersion optics for spectral analysis of water impurities

This paper reports a microfluidic device that integrates electrical and optical features required for field-portable water-chemistry testing by discharge spectroscopy. The device utilizes a dc-powered spark between a metal anode and a liquid cathode as the spectral source. Impurities are sputtered from the water sample into the microdischarge and characteristic atomic transitions due to them are detected optically. A blazed grating is used as the dispersion element. The device is fabricated from stacked glass layers, and is assembled and used with a charge-coupled device (CCD) sensing element to distinguish atomic spectra. Two structural variations and optical arrangements are reported. Detection of Cr and other chemicals in water samples has been successfully demonstrated with both devices. The angular resolution in terms of angular change per unit variation in wavelength (/spl part//spl theta///spl part//spl lambda/) is experimentally determined to be approximately 0.10 rad//spl mu/m, as opposed to the idealized theoretical estimate of 0.22 rad//spl mu/m. This is because the microdischarge is uncollimated and not a point source. However, this is sufficient angular resolution to allow critical spectra of metal impurities to be distinguished.