Franck Vincent

Planar microcoil-based microfluidic NMR probes

Microfabricated small-volume NMR probes consisting of electroplated planar microcoils integrated on a glass substrate with etched microfluidic channels are fabricated and tested. 1H NMR spectra are acquired at 300 MHz with three different probes having observed sample volumes of respectively 30, 120, and 470 nL. The achieved sensitivity enables acquisition of an 1H spectrum of 160 microg sucrose in D2O, corresponding to a proof-of-concept for on-chip NMR spectroscopy. Increase of mass-sensitivity with coil diameter reduction is demonstrated experimentally for planar microcoils. Models that enable quantitative prediction of the signal-to-noise ratio and of the influence of microfluidic channel geometry on spectral resolution are presented and successfully compared to the experimental data. The main factor presently limiting sensitivity for high-resolution applications is identified as being probe-induced static magnetic field distortions. Finally, based on the presented model and measured data, future performance of planar microcoil-based microfluidic NMR probes is extrapolated and discussed.

High-Q factor RF planar microcoils for micro-scale NMR spectroscopy

We present the design, fabrication and test of high-Q factor radiofrequency planar microcoils for nuclear magnetic resonance (NMR) spectroscopy in small volume samples. The coils are fabricated on glass wafers using high-aspect ratio SU-8 photoepoxy and copper electroplating. On-wafer electrical characterization shows quality factors up to 40 at 800 MHz. A 500 μm diameter microcoil with a measured quality factor of 24 at 300 MHz is mounted on a printed circuit board and electrically contacted using aluminum wire bonding. This probe is inserted in a 7 T-superconducting magnet, and a 1H-NMR spectrum of 160 nl ethylbenzene contained in a capillary placed over the microcoil is acquired in a single scan. This work is an important step towards the integration of NMR detection into micro-total analysis systems (μTAS).

Low-power 2-D fully integrated CMOS fluxgate magnetometer

In this paper, we present a low-power, two-axis fluxgate magnetometer. The planar sensor is integrated in a standard CMOS process, which provides metal layers for the coils and electronics for the signal extraction and processing. The ferromagnetic core is placed diagonally above the four excitation coils by a compatible photolithographic post process, performed on a whole wafer. The sensor works using the single-core principle, with a modulation technique to lower the noise and the offset at the output. In contrast to traditional fluxgate approaches, the sensor features a high degree of integration and minimal power consumption at 2.5 V of supply voltage that makes it suitable for portable applications. A novel digital feedback principle is integrated to linearize the sensor characteristics and to extend the linear working range.

Electron-spin resonance probe based on a 100 μm planar microcoil

We describe the fabrication and the performance of a microcoil-based probe for electron spin resonance (ESR) spectroscopy on micrometer sized samples. The probe consists of a 100 μm planar microcoil fabricated on a glass substrate, tuned and matched at 1.4 GHz (L band) using miniaturized ceramic capacitors. We performed continuous wave ESR experiments on samples having a volume between (100 μm)3 and (10 μm)3. At 300 K, we achieved a spin sensitivity of about 1010 spins/G Hz1/2, which is comparable to that of commercial ESR spectrometers operating at 9 GHz (X band). The results reported in this article suggest that microcoil-based probes might represent a valid alternative to conventional microwave cavities for ESR studies of sample of the order of (100 μm)3 and smaller.

Planar microcoil-based magnetic resonance imaging of cells

We report magnetic resonance images of biological cells and cellular aggregates obtained in vitro using high-Q factor microfabricated planar coils at 500 MHz. An image of a /spl sim/1 mm diameter frog oocyte is acquired using a 500-/spl mu/m microcoil, high-resolution images of intact mouse pancreatic islets(/spl sim/100 /spl mu/m size) are successfully acquired for the first time. Due to their planer nature, compatibility with on-chip cell culturing methods and enhanced sensitivity for microscopic samples, micromachined coils will prove essential to perform further Magnetic Resonance studies at the cellular level.

A Microfabricated Probe with Integrated Coils and Channels for on-Chip NMR Spectroscopy

We present the development of a monolithic NMR probe fabricated on a glass substrate, combining an integrated high-quality factor, multi-turn planar coil with a microfluidic network. Concentrations of a few percent ethanol in water can be detected by 1H NMR in a 30-nL volume with only 3 scans.

A novel planar magnetic sensor based on orthogonal fluxgate principle

In this paper, we present a new planar fluxgate magnetometer structure. The sensor has the orthogonal fluxgate configuration which makes the detection part independent of the excitation mechanism. The sensor consists of a ferromagnetic cylindrical core covering an excitation rod, and planar coils for signal detection. The fabricated sensor has a linear range of /spl plusmn/ a sensitivity of 4.3 mV/mT, and a perming below 400 nT for 200 mA peak sinusoidal excitation current at 100 kHz. The effect of demagnetization on the sensitivity, linear range, and perming for this structure is demonstrated by varying the length of the ferromagnetic core.

Low noise CMOS micro-fluxgate magnetometer

We present a new two-axis fluxgate magnetometer fully integrated in CMOS technology. The magnetometer exhibits excellent sensitivity of 2700 V/T and the magnetic equivalent noise spectral density of 6nT//spl radic/Hz at 1 Hz. The total power consumption is as low as 35 m W from the single 5 V power supply. The low noise characteristic is obtained using the combination of good magnetic . material properties and electronic post-modulation technique to reduce the noise coming from CMOS electronic part.

High Sensitivity Hall Magnetic Sensors Using Planar Micro and Macro Flux Concentrators

We have studied the sensitivity of Hall devices using planar magnetic flux concentrators of various lengths. By placing magneto-concentrators (MCs) on Hall device, we obtained sensitivity up to 100 V/T for a bias current of 1 mA and for a length of the MCs of 50 mm. This value is about 1000 times better then that of a conventional silicon Hall devices, without adding significant amount of noise. The magnetic gain is achieved using a combination of micro-integrated and macroscopic magnetic flux concentrators.

An Orthogonal Fluxgate-Typemagnetic Microsensor

In this paper, we present a new microfabricated orthogonal fluxgate sensor structure. The sensor consists of an electroplated copper excitation rod surrounded by an electroplated permalloy layer and has planar pick-up coils for signal detection. The use of electroplating leads to a low-cost fabrication process and the use of planar pick-up coils provides easy integration with CMOS processes. The fabricated sensor has an excitation independent linear range of ± 100 µ T, a sensitivity of 280 µ V/mT, and an average power dissipation of 0.8 mW for 30 mA-peak sinusoidal excitation current at 100 kHz frequency.