Christophe Yamahata

Plastic micropump with ferrofluidic actuation

We present the realization and characterization of a new type of plastic micropump based on the magnetic actuation of a magnetic liquid. The pump consists of two serial check-valves that convert the periodic motion of a ferrofluidic plug into a pulsed quasi-continuous flow. The ferrofluid is actuated by the mechanical motion of an external NdFeB permanent magnet. The water-based ferrofluid is synthesized in-house using a coprecipitation method and has a saturation magnetization of 32 mT. The micropump consists of various layers of polymethylmethacrylate (PMMA), which are microstructured by powder blasting or by standard mechanical micromachining techniques, and are assembled in a single plastic structure using a monomer gluing solution. Two soft silicone membranes are integrated in the microfluidic structure to form two check-valves. Water has been successfully pumped at flow rates of up to 30 /spl mu/L/min and pumping is achieved at backpressures of up to 25 mbar.

Silicon Nanotweezers With Subnanometer Resolution for the Micromanipulation of Biomolecules

We describe electrostatically actuated silicon nanotweezers which are intended for the manipulation and characterization of filamentary molecules. The microelectromechanical system consists of a pair of opposing tips whose distance can be accurately adjusted by means of an integrated differential capacitive sensor. The fabrication process is based on silicon-on-insulator technology and combines KOH wet anisotropic etching and deep reactive ion etching of silicon to form sharp nanotips and high aspect ratio microstructures, respectively. In the designed prototype, the initial gap between the tips was around 20 mum. The device showed a maximum displacement of about 2.5 mum, and we could achieve a resolution better than 0.2 nm (in static mode). We measured a resonant frequency of 2.5 kHz and a quality factor (Q factor) of 50 in air. The instrument was used to perform static and dynamic mechanical manipulations on DNA molecules, and we could distinctly observe the viscoelastic behavior of DNA bundles from these experiments.

Subnanometer Translation of Microelectromechanical Systems Measured by Discrete Fourier Analysis of CCD Images

In-plane linear displacements of microelectromechanical systems are measured with subnanometer accuracy by observing the periodic micropatterns with a charge-coupled device camera attached to an optical microscope. The translation of the microstructure is retrieved from the video by phase-shift computation using discrete Fourier transform analysis. This approach is validated through measurements on silicon devices featuring steep-sided periodic microstructures. The results are consistent with the electrical readout of a bulk micromachined capacitive sensor, demonstrating the suitability of this technique for both calibration and sensing. Using a vibration isolation table, a standard deviation of σ = 0.13 nm could be achieved, enabling a measurement resolution of 0.5 nm (4σ) and a subpixel resolution better than 1/100 pixel.

A high-performance compact electromagnetic actuator for a PMMA ball-valve micropump

We present the microfabrication and characterization of a reciprocating-type poly(methylmetacrylate) (PMMA) ball-valve micropump which is actuated with a high-performance and compact electromagnetic circuit of centimeter size. We have improved by finite element calculations the magnetic design of the electromagnet that actuates a NdFeB permanent magnet embedded in a poly(dimethylsiloxane) (PDMS) pumping membrane. Powder blasting technology and conventional micromachining techniques are employed for the microstructuring of PMMA layers. The ball-valve micropump is bubble tolerant and has self-priming capabilities. It has a resonant frequency of around 20 Hz, and it exhibits a backpressure up to 37 kPa; water is pumped at flow rates up to 6.8 mL min−1 for a 2 W electromagnetic actuation power. The actuation frequency dependence of the flow rate can be well described by a fluidic damped oscillator model.

Pumping of mammalian cells with a nozzle-diffuser micropump

We discuss the successful transport of jurkat cells and 5D10 hybridoma cells using a reciprocating micropump with nozzle-diffuser elements. The effect of the pumping action on cell viability and proliferation, as well as on the damaging of cellular membranes is quantified using four types of well-established biological tests: a trypan blue solution, the tetrazolium salt WST-1 reagent, the LDH cytotoxicity assay and the calcium imaging ATP test. The high viability levels obtained after pumping, even for the most sensitive cells (5D10), indicate that a micropump with nozzle-diffuser elements can be very appropriate for handling living cells in cell-on-a-chip applications.

Silicon Nanotweezers with Adjustable and Controllable Gap for the Manipulation and Characterization of DNA Molecules

We describe electrostatically actuated silicon nanotweezers which are intended for the manipulation and characterization of DNA molecules. The fabrication process combines KOH etching and deep reactive ion etching (DRIE) on silicon-on-insulator (SOI) wafer to form sharp nanotips and high aspect ratio microstructures, respectively. The microelectromechanical system (MEMS) consists of a pair of opposing tips, the distance of which can be accurately adjusted thanks to a high resolution differential capacitive sensor. The device shows a resolution of 5 nm for a displacement range of 3 mum (static mode). It has a resonant frequency at 2 kHz and a quality factor of 40 in air, and 550 in vacuum

Three-Phase Electrostatic Rotary Stepper Micromotor With a Flexural Pivot Bearing

Electrostatic stepper motors, also known as synchronous variable-capacitance motors, operate by utilizing the electrical energy stored in the variable capacitances formed between the poles of their rotor and stator. We present the design, modeling, and experimental characterization of a three-phase rotary stepper micromotor that employs a flexural suspension of the rotor to avoid any frictional contact during operation, providing precise, repeatable, and reliable bidirectional stepping motion without feedback control. A monolithic micromotor with high-aspect-ratio poles and an integrated three-phase electrical network was fabricated in a standard single-crystal silicon wafer by combining vertical trench isolation and bulk micromachining. The experimental characterization of a prototype having a diameter of 1.4 mm has demonstrated a rotational range of 26° (±13°) at 75 V and a maximum speed of 1.67°/ ms. Half-stepping and microstepping operation modes were demonstrated with step sizes of 1/6° and 1/48°, respectively. The exceptional performance of the motor makes it suitable for use in hard-disk drives as a secondary stage actuator to maintain a constant orientation between the read/write head and the recording tracks.

Electrostatic Rotary Stepper Micromotor for Skew Angle Compensation in Hard Disk Drive

Circular data tracks in present-day hard disk drives (HDD) are accessed by a read/write head mounted on a support arm, which is swung by a voice coil drive. The orientation of the head relative to a data track varies with the radial position of the track, causing an increase in data track misregistration and limiting the performance of HDD. We present a rotary micromotor which can be used as a secondary stage actuator to maintain a constant orientation between the head and the tracks during disk operation. This electrostatic stepper micromotor, bulk micromachined in a standard monocrystalline silicon wafer, uses flexure pivots to avoid any frictional contact of the rotor, providing precise, repeatable and reliable bidirectional stepping motion without feedback control. The experimental characterization of a prototype having a diameter of 1.4 mm has demonstrated a rotational range of 26° (+/- 13°) at 75 V, a resolution of 1/6° in a coarse stepping mode and a maximum speed of 1.67°/ms.

High-Performance Shuffle Motor Fabricated by Vertical Trench Isolation Technology

Shuffle motors are electrostatic stepper micromotors that employ a built-in mechanical leverage to produce large output forces as well as high resolution displacements. These motors can generally move only over predefined paths that served as driving electrodes. Here, we present the design, modeling and experimental characterization of a novel shuffle motor that moves over an unpatterned, electrically grounded surface. By combining the novel design with an innovative micromachining method based on vertical trench isolation, we have greatly simplified the fabrication of the shuffle motors and significantly improved their overall performance characteristics and reliability. Depending on the propulsion voltage, our motor with external dimensions of 290 μm × 410 mm displays two distinct operational modes with adjustable step sizes varying respectively from 0.6 to 7 nm and from 49 to 62 nm. The prototype was driven up to a cycling frequency of 80 kHz, showing nearly linear dependence of its velocity with frequency and a maximum velocity of 3.6 mm/s. For driving voltages of 55 V, the device had a maximum travel range of ±70 μm and exhibited an output force of 1.7 mN, resulting in the highest force and power densities reported so far for an electrostatic micromotor. After five days of operation, it had traveled a cumulative distance of more than 1.5 km in 34 billion steps without noticeable deterioration in performance.

An electrostatic 3-phase linear stepper motor fabricated by vertical trench isolation technology

We present the design, microfabrication and characterization of an electrostatic 3-phase linear stepper micromotor constructed with vertical trench isolation technology. This suitable technology was used to create a monolithic stepper motor with high-aspect-ratio poles and an integrated 3-phase electrical network in the bulk of a standard single-crystal silicon wafer. The shuttle of the stepper motor is suspended by a flexure to avoid any mechanical contact during operation, enhancing the precision, repeatability and reliability of the stepping motion. The prototype is capable of a maximum travel of +/−26 µm (52 µm) at an actuation voltage of 30 V and a step size of 1.4 µm during a half-stepping sequence.