Victor Samper

Fabrication of a dielectrophoretic chip with 3D silicon electrodes

This paper describes a device in which the DEP electrodes form the channel walls. This is achieved by fabricating microfluidic channel walls from highly doped silicon so that they can also function as DEP electrodes. The device is fully enclosed and there is no fluidic leakage due to lead-outs. The electrode arrangement minimized the electrical dead volumes such that the DEP force is always sufficient to overcome Stokes force and concentrate the cells and beads at the nominal operating potential of 25 Vp–p. The device has been tested successfully with yeast cells. When the actuation signal was increased to 13 Vp–p, cells began to move towards the tip of the DEP electrodes, where the electric field gradient was highest. As the actuation voltage increased, the cells moved faster. For 25 Vp–p, a stable equilibrium of cell concentration pattern was achieved in 10–13 s.

Microcoils for transport of magnetic beads

Integrated magnetic devices were fabricated, consisting of arrays of microcoils of a novel structure, embedded in a silicon substrate, with small conductors asymmetrically shaped and with ferromagnetic pillars made of a magnetic alloy (NiCoP) as magnetic cores. These structures generated large magnetic field gradients that very effectively attracted magnetic beads. By alternatively injecting currents in an array of such microcoils placed in a microfluidic chamber, magnetic beads were guided in different movement modes and step sizes in a continuous flow.

Fabrication of three-dimensional magnetic microdevices with embedded microcoils for magnetic potential concentration

Novel magnetic microdevices were developed for magnetic field generation and concentration and successfully characterized and tested for magnetic potential focusing which is very important for various MEMS applications such as magnetic particles manipulation. These microdevices have been fabricated using an innovative processing sequence which eliminates many problems associated with other fabrication techniques and provides a platform for adding other subsequent fabrication steps required to integrate the microcoils with other microcomponents. They consist of high aspect ratio planar coils made of electroplated copper embedded in the silicon substrate, with ferromagnetic pillars and backside plates made of a CoNiP ternary alloy. A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio of each single conductor and the ferromagnetic pillars positioned at high flux density locations. This arrangement creates very steep magnetic potential wells, in particular at the vicinity of the pillars. The manipulation of micromagnetic particles in a static and continuous flow conditions has been demonstrated.

Ferroelectric properties and leakage current characteristics of radio-frequency-sputtered SrBi2(V0.1Nb0.9)2O9 thin films

The ferroelectric properties and leakage current mechanisms of polycrystalline SrBi2(V0.1Nb0.9)2O9(SBVN) thin films, which were deposited on Pt∕SiO2∕n-Si substrate by rf-magnetron sputtering and then annealed at 700°C for 60min in air, were investigated. These SBVN films showed excellent ferroelectric properties in terms of a large remnant polarization (2Pr) of ∼25μC∕cm2(2Ec∼200kV∕cm), fatigue free characteristics up to ⩾108 switching cycles and a low current density of 10−8A∕cm2 at 100kV∕cm. X-ray diffraction and scanning electron microscope investigations indicate that the sputtered films exhibit a dense, well crystallized microstructure having random orientations and with a rather smooth surface morphology. The improved ferroelectric and leakage current characteristics obtained at the low processing temperature are attributed to the larger polarizability attained through increased rattling space in the distorted Nb(V)O6 of the perovskite block due to the partial substitution of Nb with smaller V ions. ...

Precise profile control of 3D lateral junction traps by 2D mask layout and isotropic etching

This study demonstrates precise profile control of 3D lateral junction traps in silicon by exploiting a 2D mask layout and isotropic etching. The traps penetrate through silicon partitions and laterally link microfluidic channels. Since the trap constrictions cannot be registered directly by planar lithography, they are not trivial to define but critical for capturing cells in suspension. A special mask layout introduced here when combined with isotropic etching can form elliptic and circular constrictions. The mask layout offers three design parameters: two geometric angles and a separation distance between them. The design parameters have been systematically varied and a set of corresponding trap structures have been fabricated. Mapping of the constriction profiles to design parameters indicates that the constriction shape is mainly determined by the two design angles whereas the constriction size is controlled by the separation distance and total isotropic etching. It is shown that a circular constriction can be fabricated by setting the two angles such that their harmonic mean yields a critical value of about 45°. The constriction size may vary from several micrometers to tenths of micrometers depending on the separation distance and isotropically etched amount.

EVALUATION OF CURRENT-CARRYING WIRES FOR MANIPULATION OF MAGNETIC MICRO/NANOPARTICLES FOR BIOMEDICAL APPLICATIONS

In this study we present a set of guidelines for the design of current carrying micro-conductors/micro-coils (MCs) for magnetic nanoparticles manipulation in biomedical applications. Precise spatial manipulation requires steep magnetic field gradients and due to the consequences of scaling laws, these gradients should be maximized as the size of the particle reduces. Conventional planar coils have many construction and functional limitations, such as generating only small magnetic field gradients, Joule heating, and limited ability to move particles with high spatial resolution. On the other hand, micro-coils can provide a satisfactory solution to all these problems. The geometrical and structural parameters play significant roles in determining the ability to move guide and transport nanoparticles. Design guidelines were generated from a detailed theoretical treatment and finite element analysis (FEA). The spatial distributions of magnetic fields, field gradients and magnetic forces on particles were simulated using FEA for different geometrical/structural parameters and wire arrangements. An array of wires create a chain of magnetic potential wells that are controllable in terms of magnitude and direction and therefore can be used to control the motion and position of magnetic nano-particles by tuning the current through the array.

Dielectrophoretic chip with bulk silicon electrodes

In this work we present the dielectrophoretic structure fabricated using two glass wafers and one 0.5 mm thick and highly conductive silicon wafer. In fabricated device the DEP force extends uniformly across the volume of the microfluidic device in the direction normal to the wafer plane. This is achieved by fabricating microfluidic channel walls from doped silicon so that they can also function as DEP electrodes. The advantages of the structure are: electrical leadouts that are free from the fluid leakage usually associated with the lead out recesses, a volume DEP force for deep chambers compared with the surface forces achieved by planar electrodes, no electrical dead volumes as encountered above the thin planar electrodes of alternative technologies, biocompatible silicon oxide passivated surfaces, and no electrochemical effects that arise from edge effects in multi-metal electrodes such as Ti/Au or Cr/Au.

Potentiostatic deposition and detection of DNA on conductive nitrogen doped diamond-like carbon film electrode

We describe the electrochemical oxidation of deoxyribonucleic acid (DNA) at a conductive nitrogen doped diamond-like carbon (N-DLC) film electrode, and a procedure for reversible adsorption of DNA onto the N-DLC film electrode under potentiostatic control. N-DLC film electrode has well defined higher oxidation responses of guanine and adenine of denatured DNA compared to the response at a glassy carbon electrode. DNA can be deposited at the N-DLC film electrode when the electrode is positively charged and be released when the electrode is negatively charged. The N-DLC film electrode has an optimum deposition potential for DNA. The preliminary work shows that N-DLC film would be a novel electrode material for extraction and detection of DNA, which can be used for bio-micro-systems for DNA detection.

Microfabrication of A Si Mesh Structure Depth Filter

The uTAS proposed the full incorporation of analytical procedures, which include sampling, sample preparation or pretreatment and actual analysis, into flowing systems. To incorporate a full uTAS, it is important to develop the individual microfluidic components. Microfilter is one of the microfluidic devices for sample preparation. This paper presents a fabrication method for a vertical silicon mesh structure depth filter as well as the application of white blood cell filtration. The results are also compared with another fabricated horizontal flow silicon filter.

Voltage monitoring hydrostatic pressure method for measuring the force sensitivity of piezoelectric films

A simple nondestructive method for measuring the force sensitivity of freestanding piezoelectric films is presented. The principle used is the direct piezoelectric effect, and the force sensitivity of the film is calculated by measuring the charge generated across the film and the magnitude of the applied pressure. A hydrostatic pressure is generated by pressurizing the oil in the chamber using a voice coil actuator. This method is capable of measuring the force sensitivity in the range of millinewton with a simple sample preparation in the form of a parallel plate capacitor structure. This straightforward measurement also results in improved electrical characterization of the piezoelectric capacitor and is suitable for the low-cost testing of microelectromechanical systems.