Fabrication of ultralow-profile micromachined inductor with magnetic core material

We have fabricated a microinductor with an ultralow profile by a microelectromechanical systems (MEMS) technique. The fabrication process uses UV-LIGA, dry etching, fine polishing, and electroplating to achieve high performance. The dimensions of the inductor are 1500 /spl mu/m/spl times/900 /spl mu/m/spl times/100 /spl mu/m. It has 41 turns, with coil width of 20 /spl mu/m, space of 20 /spl mu/m, and a high aspect ratio of 5 : 1. The inductance is 0.424 /spl mu/H and the quality factor (Q factor) is about 1.7 at a frequency of 1 MHz. The stray capacitance is approximately zero over the frequency range measured.     

High-temperature and broadband immersion ultrasonic probes

Immersion ultrasonic probes for measurements and imaging at high temperature are presented. The probes consist of sol-gel-sprayed thick films as piezoelectric ultrasonic transducers (UTs) directly deposited onto steel buffer rods. They operate in pulse-echo mode at temperatures up to 500/spl deg/C. The operating ultrasonic frequency is between 5 MHz and 20 MHz, controlled by the film thickness. The ultrasonic thickness measurement of a steel plate with the probe fully immersed in molten zinc at 450/spl deg/C was demonstrated using ultrasonic plane waves. For imaging purposes, the probing end of the steel buffer rod was machined into a semispherical concave shape to form an ultrasonic lens and achieve high spatial resolution with focused ultrasound in liquids. Ultrasonic surface and subsurface imaging using a mechanical raster scan of the focused probe in silicone oil at 200/spl deg/C was also carried out. The importance of the signal-to-noise ratio (SNR) in the pulse-echo measurement is discussed.     

A low-noise latching comparator probe for waveform sampling applications

A new latching comparator probe is described. The probe is being developed as part of an effort to augment voltage measurement capability in the 10 Hz to 1 MHz frequency range. The probe offers an input voltage range of /spl plusmn/10 V, input impedance of 1 M/spl Omega/ and root mean square noise referred to the input as low as 55 /spl mu/V. The probe's 3-dB bandwidth is approximately 20 MHz. Total harmonic distortion is as low as -93 dB at 50 kHz. Gain flatness is within /spl plusmn/10 /spl mu/V/V from 100 Hz to 100 kHz. Improved step settling performance is achieved using a technique that minimizes circuit thermal errors. The probe's input range can be extended with a frequency-compensated 1-M/spl Omega/ input impedance attenuator allowing measurement of pulses in the microsecond regime up to 100 V. The attenuator can be compensated further with a digital filtering algorithm to achieve gain accuracy better than 100 /spl mu/V/V.     

Low temperature fabrication of immersion capacitive micromachined ultrasonic transducers on silicon and dielectric substrates

A maximum processing temperature of 250/spl deg/C is used to fabricate capacitive micromachined ultrasonic transducers (CMUTs) on silicon and quartz substrates for immersion applications. Fabrication on silicon provides a means for electronics integration via post-complementary metal oxide semiconductor (CMOS) processing without sacrificing device performance. Fabrication on quartz reduces parasitic capacitance and allows the use of optical displacement detection methods for CMUTs. The simple, low-temperature process uses metals both as the sacrificial layer for improved dimensional control, and as the bottom electrode for good electrical conductivity and optical reflectivity. This, combined with local sealing of the vacuum cavity by plasma-enhanced chemical-vapor deposition of silicon nitride, provides excellent control of lateral and vertical dimensions of the CMUTs for optimal device performance. In this paper, the fabrication process is described in detail, including process recipes and material characterization results. The CMUTs fabricated for intravascular ultrasound (IVUS) imaging in the 10-20 MHz range and interdigital CMUTs for microfluidic applications in the 5-20 MHz range are presented as device examples. Intra-array and wafer-to-wafer process uniformity is evaluated via electrical impedance measurements on 64-element ring annular IVUS imaging arrays fabricated on silicon and quartz wafers. The resonance frequency in air and collapse voltage variations are measured to be within 1% and 5%, respectively, for both cases. Acoustic pressure and pulse echo measurements also have been performed on 128 /spl mu/m/spl times/32 /spl mu/m IVUS array elements in water, which reveal a performance suitable for forward-looking IVUS imaging at about 16 MHz.     

Effects of thickness and heat treatments on giant magnetoimpedance of electrodeposited cobalt on silver wires

We studied the effects of thickness and heat treatments on giant magnetoimpedance (GMI) of cobalt-coated silver wires from 1 kHz to 100 MHz, under axial static magnetic field of 2 kOe. Cobalt, of thickness ranging from 1 to 25 /spl mu/m, was electro-deposited on 47.7-/spl mu/m-diameter silver wires. The frequency dependence of GMI varied with cobalt thickness with a maximum of 176% in 10-/spl mu/m-thick cobalt at the characteristic frequency 2 MHz. The characteristic frequency decreased with increasing thickness of cobalt layer but it was rather insensitive to dc Joule heating and conventional furnace annealing. However, both heat treatments led to magnetic hardening and decrease in GMI ratio. Joule heating also induced anisotropy in wire structures normally dominated by axial anisotropy.     

Frequency- and intensity-noise measurements of a widely tunable 2-/spl mu/m Tm-Ho:KYF laser

The measurement of the frequency and intensity noise in a novel single-mode 2-/spl mu/m Tm-Ho:KYF laser is presented. The laser frequency noise is measured by exploiting the fringe side of the transmission of a Fabry-Pe/spl acute/rot interferometer. The measured power spectral density of the frequency noise is principally characterized by a random-walk noise contribution, which sets an emission linewidth of /spl sim/ 600 kHz for the 2-/spl mu/m radiation. The relative intensity noise (RIN) reaches the quantum limit of -155 dB/Hz for Fourier frequencies above 1 MHz and shows a maximum level of -90 dB/Hz at the relaxation-oscillation frequency of 20 kHz.     

Improved capacitance measurements with respect to a 1-pF cross-capacitor from 200 to 2000 Hz

This paper describes frequency dependence measurements of fused-silica capacitance standards from 200 to 2000 Hz, using a 1-pF cross-capacitor as the reference. The measured frequency dependence of fused-silica capacitors was found to vary significantly, ranging from a change of less than 0.2 /spl mu/F/F for one standard to a change of 0.8 /spl mu/F/F for another over the frequency range. Increasing capacitances with decreasing frequency from 1592 Hz for all tested fused-silica capacitors indicates that dielectric relaxation due to dielectric bulk and/or interfacial defects is the dominant source of frequency dependence. The relative combined standard uncertainty at 200 Hz (the largest in the frequency range) is 0.07 /spl mu/F/F, which is smaller by about a factor of three than the uncertainty reported previously from the National Institute of Standards and Technology (NIST).     

Dielectrophoretic assembly of carbon nanofiber nanoelectromechanical devices

We report a technique for the assembly of bottom-up nanomechanical devices. This technique employs the dielectrophoretic manipulation of nanostructures within a multiple layer lithography process. Mechanical resonators were specifically produced by assembling and clamping tubular carbon fibers onto prefabricated pads. Our preliminary results showed that an assembled cantilevered fiber with length L=5 /spl mu/m and width of W=180 nm possessed a resonant frequency of f=1.17 MHz. A shorter L=3-/spl mu/m-long singly clamped resonator of similar width showed a resonance of f=3.12 MHz. This frequency range is in agreement with the low gigapascal bending moduli previously reported for carbon structures showing extensive volume defects. This technology would allow the integration of bottom-up nanostructures with other more established fabrication processes, thus allowing the deployment of engineered nanodevices in integrated systems.     

Acoustic imaging of thick biological tissue

Up to now, biomedical imaging with ultrasound for observing a cellular tissue structure has been limited to very thinly sliced tissue at very high ultrasonic frequencies, i.e., 1 GHz. In this paper, we present the results of a systematic study to use a 150 to 200 MHz frequency range for thickly sliced biological tissue. A mechanical scanning reflection acoustic microscope (SAM) was used for obtaining horizontal crosssectional images (C-scans) showing cellular structures. In the study, sectioned specimens of human breast cancer and tissues from the small intestine were prepared and examined. Some accessories for biomedical application were integrated into our SAM (Sonix HS-1000 and Olympus UH-3), which operated in pulse-wave and tone-burst wave modes, respectively. We found that the frequency 100 to 200 MHz provides optimal balance between resolution and penetration depth for examining the thickly sliced specimens. The images obtained with the lens focused at different depths revealed cellular structures whose morphology was very similar to that seen in the thinly sectioned specimens with optical and scanning acoustic microscopy. The SAM operation in the pulse-echo mode permits the imaging of tissue structure at the surface, and it also opens up the potential for attenuation imaging representing reflection from the substrate behind the thick specimen. We present such images of breast cancer proving the method?s applicability to overall tumor detection. SAM with a high-frequency tone-burst ultrasonic wave reveals details of tissue structure, and both methods may serve as additional diagnostic tools in a hospital environment.     

220-MHz monolithically integrated optical sensor with large-area integrated PIN photodiode

We propose a PIN photodiode integrated in a BiCMOS process which combines a quantum efficiency of nearly 100% for red light, fast response times, and a low junction capacitance. Bandwidths of 720 MHz at 660 nm and 683 MHz at 850 nm are achieved for this PIN photodiode. It allows the design of fast optoelectronic integrated circuits for many advanced applications in optical sensing, optical storage systems, and optical data transmission for optical wavelengths ranging at least from 660 to 850 nm. Because of the low photodiode capacitance of 0.01 fF//spl mu/m/sup 2/, it is possible to achieve high bandwidths, even with large photodetector areas. The proposed optical receiver employing a PIN photodiode with a diameter of 500 /spl mu/m and a capacitance of only 2.2 pF attains a -3-dB bandwidth of 220 MHz, which corresponds to a maximum nonreturn-to-zero data rate of 300 Mbit/s.     

Electrode microchamber for noninvasive perturbation of mammalian cells with nanosecond pulsed electric fields

Nanosecond pulsed electric fields can pass through the external membrane of biological cells and disturb fast-responding intracellular structures and processes. To enable real-time imaging and investigation of these phenomena, a microchamber with integral electrodes and optical path for observing individual cells exposed to ultrashort electric pulses was designed and fabricated utilizing photolithographic and microelectronic methods. SU-8 photoresist was patterned to form straight sidewalls from 10 to 30 /spl mu/m in height, with gold film deposited on the top and sidewalls for conductive, nonreactive electrodes and a uniform electric field. Channel dimensions (10-30 /spl mu/m/spl times/100 /spl mu/m/spl times/12000 /spl mu/m) are suitable for observations of mammalian cells during nanosecond, megavolt-per-meter pulsed electric field exposure. Experimental studies utilizing the electrode microchamber include live-cell imaging of nanoelectropulse-induced intracellular calcium bursts and membrane phospholipid translocation.     

Ultrasound characterization of coronary artery wall in vitro using temperature-dependent wave speed

Temperature dependence of the speed of sound, /spl part/c//spl part/T, is examined as a parameter to characterize tissue-equivalent phantoms and coronary artery tissue in vitro. The experimental system comprises an ultrasound biomicroscope, operating at center frequency of 50 MHz, and a temperature controlled micropositioning sample cell. Radio frequency (RF) backscattered signals were recorded, with a digital oscilloscope, from 64 independent positions and at 5 temperatures starting at 31/spl deg/C (phantom) and 36/spl deg/C (tissue) in steps of one degree. Time shift per degree Celsius (/spl part/t//spl part/T) was obtained with a correlation technique applied between gated sections of two RF-signals collected with one degree temperature difference from the same location in the sample. The average , calculated for every position of the gated sections along the propagation axis of the ultrasound beam, has the slope proportional to the difference between the linear coefficient of thermal expansion and the thermal sensitivity of the speed of sound. Calibration measurements of /spl part/c//spl part/T, made with single- and three-layer tissue equivalent phantoms, correlated well (r/spl ges/0.91) with those measured by the time-of-flight substitution method. The /spl part/c//spl part/T was estimated for the three layers on the wall of eight samples of human coronary arteries, obtained at autopsy from four individuals. The /spl part/c//spl part/T for the intima layers decreases as the disease progresses from mild intimal thickening to a more advanced atherosclerosis.     

Plasma-sprayed MnZn ferrites with insulated fine grains and increased resistivity for high-frequency applications

Plasma-sprayed MnZn ferrite thick films are built up by splats, which consist of columnar grains with diameter /spl sim/200 nm and height /spl sim/1 /spl mu/m. The existence of the conductive wustite FeO in the as-sprayed films greatly reduces the dc resistivity. However, a useful structure can be developed in these ferrite films with fine equal-axis ferrite grains insulated by the high-resistivity hematite Fe/sub 2/O/sub 3/ because of the polygonization of the columnar grains and the oxidation of the wustite during an annealing process. The dc resistivity increases significantly after the annealing process, an effect ascribed to the growth of hematite Fe/sub 2/O/sub 3/ on the basis of impedance analysis. The magnetic properties of these ferrite films improve concurrently. The high-frequency response of the annealed plasma-sprayed MnZn ferrites shows a permeability of /spl sim/700 stabilized to above 10 MHz. The maximum Q factor at about 10 MHz increases from 5 to 20 as a result of the increase of the dc resistivity.     

Samarium and manganese-doped lead titanate ceramic fiber/epoxy 1-3 composite for high-frequency transducer application

Samarium- (Sm) and manganese- (Mn) doped lead titanate ceramic fibers with a diameter of 35 /spl mu/m were prepared using a sol-gel method. The X-ray diffraction pattern shows that the fibers have a pure perovskite structure. The 1-3 composite disks with a thickness of 31-41 /spl mu/m and with ceramic volume fraction of /spl sim/0.68 have been prepared using the samarium and manganese doped lead titanate (PSmT) fibers. The resonance characteristics of the poled composite disks were measured. A focused transducer was fabricated using a concave 1-3 composite disk with nonuniform thickness in order to enhance its bandwidth. The insertion loss (IL), pulse-echo response and frequency spectrum of the composite transducer were measured. The center frequency of the transducer was /spl sim/31 MHz with a -3 dB bandwidth of /spl sim/123% and a low IL of 29.3 dB.     

High-temperature single-crystal 3C-SiC capacitive pressure sensor

Single-crystal 3C-silicon carbide (SiC) capacitive pressure sensors are proposed for high-temperature sensing applications. The prototype device consists of an edge-clamped circular 3C-SiC diaphragm with a radius of 400 /spl mu/m and a thickness of 0.5 /spl mu/m suspended over a 2-/spl mu/m sealed cavity on a silicon substrate. The 3C-SiC film is grown epitaxially on a 100-mm diameter <100> silicon substrate by atmospheric pressure chemical vapor deposition. The fabricated sensor demonstrates a high-temperature sensing capability up to 400/spl deg/C, limited by the test setup. At 400/spl deg/C, the device achieves a linear characteristic response between 1100 and 1760 torr with a sensitivity of 7.7 fF/torr, a linearity of 2.1%, and a hysterisis of 3.7% with a sensing repeatability of 39 torr (52 mbar). A wide range of sensor specifications, such as linear ranges, sensitivities, and capacitance values, can be achieved by choosing the proper device geometrical parameters.     

Microbubble-enhanced cavitation for noninvasive ultrasound surgery

Experiments were conducted to explore the potential of stabilized microbubbles for aiding tissue ablation during ultrasound therapy. Surgically exteriorized canine kidneys were irradiated in situ using single exposures of focused ultrasound. In each experiment, tip to eight separate exposures were placed in the left kidney. The right kidney was then similarly exposed, but while an ultrasound contrast agent was continually infused. Kidneys were sectioned and examined for gross observable tissue damage. Tissue damage was produced more frequently, by lower intensity and shorter duration exposures, in kidneys irradiated with the contrast agent present. Using 250-ms exposures, the minimum intensity that produced damage was lower in kidneys with microbubbles than those without (controls) in 10 of 11 (91%) animals. In a separate study using /spl sim/3200 W/cm/sup 2/ exposures, the minimum duration that produced damage was shorter after microbubbles were introduced in 11 of 12 (92%) animals. With microbubbles, gross observable tissue damage was produced with exposure intensity /spl ges//spl sim/800 W/cm/sup 2/ and exposure duration /spl ges/10 /spl mu/s. The overall intensity and duration tissue damage thresholds were reduced by /spl sim/2/spl times/ and /spl sim/100/spl times/, respectively. Results indicate that acoustic cavitation is a primary damage mechanism. Lowering in vivo tissue damage thresholds with stabilized microbubbles acting as cavitation nuclei may make acoustic cavitation a more predictable, and thus practical, mechanism for noninvasive ultrasound surgery.     

A CMOS focal-plane motion sensor with BJT-based retinal smoothing network and modified correlation-based algorithm

This work presents and implements a CMOS real-time focal-plane motion sensor intended to detect the global motion, using the bipolar junction transistor (BJT)-based retinal smoothing network and the modified correlation-based algorithm. In the proposed design, the BJT-based retinal photoreceptor and smoothing network are adopted to acquire images and enhance the contrast of an image while the modified correlation-based algorithm is used in signal processing to determine the velocity and direction of the incident image. The deviations of the calculated velocity and direction for different image patterns are greatly reduced by averaging the correlated output over 16 frame-sampling periods. The proposed motion sensor includes a 32/spl times/32 pixel array with a pixel size of 100/spl times/100 /spl mu/m/sup 2/. The fill factor is 11.6% and the total chip area is 4200/spl times/4000 /spl mu/m/sup 2/. The DC power consumption is 120 mW at 5 V in the dark. Experimental results have successfully confirmed that the proposed motion sensor can work with different incident images and detect a velocity between 1 pixel/s and 140,000 pixels/s via controlling the frame-sampling period. The minimum detectable displacement in a frame-sampling period is 5 /spl mu/m. Consequently, the proposed high-performance new motion sensor can be applied to many real-time motion detection systems.     

High frequency coded imaging system with RF

Coded transmission is an approach to solve the inherent compromise between penetration and resolution required in ultrasound imaging. Our goal was to examine the applicability of the coded excitation to HF (20-35 MHz) ultrasound imaging. A novel real-time imaging system for research and evaluation of the coded transmission was developed. The digital programmable coder- digitizer module based on the field programmable gate array (FPGA) chip supports arbitrary waveform coded transmission and RF echo sampling up to 200 megasamples per second, as well as real-time streaming of digitized RF data via a high-speed USB interface to the PC. All RF and image data processing were implemented in the software. A novel balanced software architecture supports real-time processing and display at rates up to 30 frames/sec. The system was used to acquire quantitative data for sine burst and 16-bit Golay code excitation at 20 MHz fundamental frequency. SNR gain close to 14 dB was obtained. The example of the skin scan clearly shows the extended penetration and improved contrast when a 35-MHz Golay code is used. The system presented is a practical and low-cost implementation of a coded excitation technique in HF ultrasound imaging that can be used as a research tool as well as to be introduced into production.     

A high-frequency, 2-D array element using thermoelastic expansion in PDMS

Optical generation of ultrasound is a promising alternative to piezoelectricity for high-frequency arrays. An array element is defined by the size and location of a laser beam focused on a suitable surface. Optical generation using the thermoelastic effect has traditionally suffered from low conversion efficiency. We previously demonstrated an increase in conversion efficiency of nearly 20 dB with an optical absorbing layer consisting of a mixture of polydimethylsiloxane (PDMS) and carbon black spin coated onto a glass microscope slide. Radiation pattern measurements with an 85 MHz spherically focused transducer indicated an array element size of 20 /spl mu/m. These measurements lacked the spatial resolution required to reveal fine details in the radiated acoustic field. Here we report radiation pattern measurements with a 5-/spl mu/m spatial sampling, showing that the radiated acoustic field is degraded by leaky Rayleigh waves launched from the PDMS/glass interface. We demonstrate that replacing the glass with a clear PDMS substrate eliminates the leaky Rayleigh waves, producing a broad and smooth radiation pattern suitable for a two-dimensional (2-D) phased array operating at frequencies greater than 50 MHz.     

Experimental spatial sampling study of the real-time ultrasonic pulse-echo BAI-mode imaging technique

The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique has been developed to inspect the seal integrity of hermetically sealed, flexible food packages. With a focused 17.3-MHz transducer acquiring radio frequency (RF) echo data in a static rectilinear stop-and-go pattern, this technique was able to reliably detect channel defects as small as 38 /spl mu/m in diameter and occasionally detect 6-/spl mu/m-diameter channels. This contribution presents our experimental spatial sampling study of the BAI-mode imaging technique with a continuous zigzag scanning protocol that simulates a real-time production line inspection method in continuous motion. Two transducers (f/2 17.3 MHz and f/3 20.3 MHz) were used to acquire RF echo data in a zigzag raster pattern from plastic film samples bearing rectilinear point reflector arrays of varying grid spacings. The average BAI-value difference (/spl Delta/BAI) between defective and intact regions and the contrast-to-noise ratio (CNR) were used to assess image quality as a function of three spatial sampling variables: transducer spatial scanning step size, array sample grid spacing, and transducer -6-dB pulse-echo focal beam spot size. For a given grid size, the /spl Delta/BAI and CNR degraded as scanning step size in each spatial dimension increased. There is an engineering trade-off between the BAI-mode image quality and the transducer spatial sampling. The optimal spatial sampling step size has been identified to be between one and two times the -6-dB pulse-echo focal beam lateral diameter.