Justin P. Black

Integrated flow sensor for in situ measurement and control of acoustic streaming in flexural plate wave micropumps

Abstract This paper presents the design, fabrication, and characterization of a micromachined flow sensor, which is integrated onto the flexural plate wave (FPW) micropump. The flow sensor and the FPW micropump represent a complex microfluidic system that is able to control the fluid flow in the device. The system was designed using a commercial software package. The microfluidic system of a size of 10×10 mm was fabricated using common fabrication techniques. The micropump is made of an aluminum, piezoelectric zinc oxide, polysilicon, and low-stress silicon nitride membrane with a typical thickness of 1–3 μm. The thermal flow sensor consists of a polysilicon heater and polysilicon–aluminum thermopiles as temperature sensors. The cold junctions of the thermopiles are located in a new design that will avoid the drift effect of the flow sensor. The results show expected flow velocity–drive voltage characteristics.

6D-2 MEMS-Enabled Miniaturized Particulate Matter Monitor Employing 1.6 GHz Aluminum Nitride Thin-Film Bulk Acoustic Wave Resonator (FBAR) and Thermophoretic Precipitator

We describe a miniaturized MEMS particulate matter (PM) monitor that employs the deposition of particulates from a sample stream onto a 1.6 GHz piezoelectric thin-film bulk acoustic wave resonator (FBAR) by means of thermophoresis, and determination of the mass deposited by measuring the resonant frequency shift of a Pierce oscillator. Real-time measurements made in an environmental chamber over several weeks and during a week-long field study in a residence showed excellent correlation with the responses of other commercial aerosol instruments. An added mass of 1 pg could be resolved with the sensor, and the level of detection was 18 mug / m3. The monitor weighs 114 g, has a volume of approximately 245 cm3, consumes less than 100 mW, and would cost less than

Detection of nanomechanical vibrations by dynamic force microscopy in higher cantilever eigenmodes

100 USD in small quantities. Efforts to further miniaturize the sensor and integrate it with a cell-phone are described.

Single-chip multiple-frequency RF microresonators based on aluminum nitride contour-mode and FBAR technologies

The authors present a method based on dynamic force microscopy to characterize subnanometer-scale mechanical vibrations in resonant micro- and nanoelectromechanical systems. The method simultaneously employs the first eigenmode of the microscope cantilever for topography imaging and the second eigenmode for the detection of the resonator vibration. Here, they apply this scheme for the characterization of a 1.6GHz film bulk acoustic resonator, showing that it overcomes the main limitations of acoustic imaging in contact-mode atomic force microscopy. The method provides nanometer-scale lateral resolution on arbitrarily high resonant frequency systems, which makes it applicable to a wide diversity of electromechanical systems.

Microsphere capture and perfusion in microchannels using flexural plate wave structures

This work reports experimental results on a new class of multiple-frequency contour-mode bulk acoustic wave aluminum nitride resonators that were co-fabricated on the same silicon chip with suspended thin film bulk acoustic resonators (FBAR). The novel contour-mode technology combined with FBAR resonators permit the fabrication of integrated single-chip RF platforms that can cover IF and RF frequencies of particular interest to the handset market. High Q ranging from 2,000 to 4,000 were demonstrated for rectangular and ring shaped contour-mode resonators in air at frequencies as high as 473 MHz. FBAR resonators with Q of 2,000 at 1.75 GHz were fabricated on the same substrate. To further prove the contour-mode technology, ladder filters at 93 and 236 MHz were demonstrated with insertion losses of 4 and 8 dB, respectively, 3 dB bandwidth of 0.3 % and high out-of-band rejection (larger than 26 dB). In addition a low phase noise (less than - 110 dBc/Hz at 10 kHz offset) oscillator was realized using a 224 MHz ring resonator in a standard pierce design.

Miniaturized multi-band filter banks for Extravehicular radio (EVA) Applications

A standing acoustic field excited by an ultrasonic flexural plate wave (FPW) device is shown to trap microspheres and cells suspended in a pressure-driven flowing liquid. Capture is achieved by counteracting the viscous drag forces on a particle with acoustic radiation pressure. The suitability of this technique for biochemical analysis is demonstrated with two experiments: (1) acoustically trapped streptavidin-coated 1 /spl mu/m microspheres conjugated to fluorescent 200 nm biotinylated microspheres; and (2) perfusion of the membrane permeant fluorescein diacetate across acoustically trapped cells. Biochemical interaction was monitored with a fluorescence microscope. Efforts to integrate acoustic traps with on-chip FPW microfluidic pumps are also described.

Mechanical detection and mode shape imaging of vibrational modes of micro and nanomechanical resonators by dynamic force microscopy

NASA seeks to employ micro-electromechanical system (MEMS) S-band filters to reduce the size, weight, and power of its reconfigurable, fault-tolerant, next-generation extravehicular activity (EVA) radio. Of particular interest to NASA are banks of channel-select filters from 2.4 - 2.483 GHz. We describe a novel double-layer contour-mode piezoelectric aluminum nitride (AlN) resonator topology that is amenable for use in GHz filter banks. Measured results of a 1.7 GHz resonator are presented, showing a motional resistance of 60 Omega and an electromechanical coupling coefficient of 0.9%. Excellent agreement with a lumped parameter model of the device is observed. Ongoing simulation and design efforts of 2.4 GHz filters employing the novel AlN resonator topology are also reviewed.

Comparison of the performance of flexural plate wave and surface acoustic wave devices as the detector in a gas chromatograph

We describe a method based on the use of higher order bending modes of the cantilever of a dynamic force microscope to characterize vibrations of micro and nanomechanical resonators at arbitrarily large resonance frequencies. Our method consists on using a particular cantilever eigenmode for standard feedback control in amplitude modulation operation while another mode is used for detecting and imaging the resonator vibration. In addition, the resonating sample device is driven at or near its resonance frequency with a signal modulated in amplitude at a frequency that matches the resonance of the cantilever eigenmode used for vibration detection. In consequence, this cantilever mode is excited with an amplitude proportional to the resonator vibration, which is detected with an external lock-in amplifier. We show two different application examples of this method. In the first one, acoustic wave vibrations of a film bulk acoustic resonator around 1.6 GHz are imaged. In the second example, bending modes of carbon nanotube resonators up to 3.1 GHz are characterized. In both cases, the method provides subnanometer-scale sensitivity and the capability of providing otherwise inaccessible information about mechanical resonance frequencies, vibration amplitude values and mode shapes.

Ultrasonic Flexural-Plate-Wave Sensor for Detecting the Concentration of Settling E. coli W3110 Cells

The sensitivity to chemical vapors of the flexural plate wave (FPW) device is compared to that of a 250 MHz surface acoustic wave (SAW) detector available with the MSI-301 Gas Chromatograph. The sensitivity of uncoated devices, and devices coated with the polymeric adsorbents polyisobutylene and polybutadiene, were compared using three vapors-methanol (CH/sub 3/OH), nitrous oxide (N/sub 2/O), and helium (He). Both the SAW and FPW sensor responses were linearly proportional to concentration with concentration. The FPW is shown to be more sensitive than the SAW for all three vapors, regardless of coating. The minimal detectable concentrations for methanol, N/sub 2/O and He were 75 ppm, 80 ppm, and 250 ppm respectively, for the FPW, and 535 ppm, 2500 ppm, and greater than 10000 ppm for the SAW. The relatively high sensitivity of the FPW is attributed to its response to both mass loading and changes in gas density.