P.-A. Besse

Detection of a single magnetic microbead using a miniaturized silicon Hall sensor

Using a highly sensitive silicon Hall sensor fabricated in a standard complementary metal-oxide-semiconductor (CMOS) technology, we detect a single magnetic microbead of 2.8 μm in diameter. The miniaturized sensor has an active area of 2.4×2.4 μm 2, a sensitivity of 175 V/AT and a resistance of 8.5 k. Two detection methods, both exploiting the superparamagnetic behavior of the bead, are experimentally tested and their performances are compared. This work opens the way to the fabrication of low cost microsystems for biochemical applications based on the use of dense arrays of silicon Hall sensors and CMOS electronics.

Single photon detector fabricated in a complementary metal-oxide-semiconductor high-voltage technology

In this article, a fully integrated single photon detector including a silicon avalanche photodiode and a quenching circuit is presented. The low doping concentrations, inherent to the complementary metal–oxide–semiconductor (CMOS) high-voltage technology used, favor the absorption of red and infrared photons at the depletion region. The detection probability rapidly increases with excess bias voltages up to 5 V. At this value, the detection probability is larger than 20% between 420 nm and 620 nm and still 7% at 750 nm. The photosensitive area is 7 μm in diameter. Cointegration of the diode and the quenching resistor allows a drastic reduction of parasitic capacitances. Though passively quenched, the single photon detector exhibits a dead time as low as 75 ns. The avalanche current is quickly quenched in less than 3.5 ns leading to a relatively low afterpulsing probability of 7.5% at 5 V excess bias voltage. The afterpulses are located in the first microseconds after the avalanche event. At room temperature, the dark count rate is about 900 Hz at 5 V excess bias voltage. Cooling of the sensor below 0 °C is of minor interest since the tunneling process becomes dominant. A remarkably short timing resolution has been obtained with values lower than 50 ps for excess bias voltage higher than 5 V. The industrial CMOS high-voltage technology used guarantees low production costs. In applications where the light can be focused on the small photosensitive area using a high magnification objective, the fabricated single photon avalanche photodiode overcomes the features of standard photomultiplier tubes. The CMOS integration opens the way to the fabrication of an extremely compact array. The design can be easily fitted to a dedicated application. Furthermore, by using an industrial CMOS process, the cointegration of data processing electronics to produce a smart sensor would be a feasible task.

The future of magnetic sensors

Abstract The operation of magnetic-field sensors is based on many different physical principles ranging from induction to magneto-optical effects. This in turn leads to a vast range of possible magnetic sensor types. What will finally decide the commercial viability of a particular magnetic sensor is its performance as well as its compatibility with miniaturization and microelectronic circuits. The magnetic sensors with the most potential for future applications include: Hall devices, magnetoresistors, inductive coils and fluxgates. The Hall device, while very compatible with microelectronics, suffers from a limited sensitivity in silicon, a high level oof 1 F noise and a relatively large offset. Ferromagnetic magnetoresistors generally have a high sensitivity at a low field; associated problems are the flipping effect and hysteresis. Inductive coils find many applications in proximity and distance sensors, but the miniaturization of coils is difficult. The fluxgate is a highly sensitive magnetic sensor. In principle, it could be integrated, but the main challenges are the three-dimensional structure of the coils and the low magnetic permeability of integrated ferromagnetic cores. The performance of sensors can be considerably improved by incorporating them into a system and using synergistic relationships such as feedback and compensation. The future of magnetic sensor microsystems looks bright with many promising application areas.

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-noise silicon avalanche photodiodes fabricated in conventional CMOS technologies

We present a simple design technique that allows the fabrication of UV/blue-selective avalanche photodiodes in a conventional CMOS process. The photodiodes are fabricated in a twin tub 0.8 /spl mu/m CMOS technology. An efficient guard-ring structure is created using the lateral diffusion of two n-well regions separated by a gap of 0.6 /spl mu/m. When operated at a multiplication gain of 20, our photodiodes achieve a very low dark current of only 400 pA/mm/sup 2/, an excess noise factor F=7 at /spl lambda/=400 nm and a good gain uniformity. At zero bias voltage, the responsivity peaks at /spl lambda/=470 nm, with 180 mA/W. It corresponds to a 50% quantum efficiency. Successive process steps are simulated to provide a comprehensive understanding of this technique.

First fully integrated 2-D array of single-photon detectors in standard CMOS technology

A two-dimensional (2-D) array (4 by 8) of single-photon avalanche diodes integrated in an industrial complementary metal-oxide-semiconductor (CMOS) process is presented. Each pixel combines a photodiode biased above its breakdown voltage in the so-called Geiger mode, a quenching resistor, and a simple comparator. The pitch between the pixels is 75 /spl mu/m and the diameter of each pixel is 6.4 /spl mu/m. The full integration allows reducing the number of charge carriers in a Geiger pulse. The electroluminescence responsible for optical crosstalks between pixels is then reduced leading to a negligible optical crosstalk probability. Thanks to the cleanness of the fabrication process, no afterpulsing effects are noticed. At room temperature, most of the pixels exhibit a dark-count rate of about 50 Hz. The detection probability is almost identical for all 32 pixels of the array with relative variation in the range of a few percents. This letter demonstrates the feasibility of an array of single-photon detectors sensitive in the visible part of the spectrum. Besides low production costs and compactness, an undeniable benefit lies in the potential to easily modify the design to fit a specific application. Furthermore, the CMOS integration opens the way to on-chip data processing.

Micro-Hall devices: performance, technologies and applications

In this review paper, we summarize the performance (in particular the magnetic field resolution), micro-fabrication technologies and applications of micrometer sized Hall effect devices. Additionally, our activities in this domain are briefly described.

New fully integrated 3-D silicon Hall sensor for precise angular-position measurements

Abstract A ± 0.3 ° precision in angular-position measurement over a 360 ° rotation has been obtained with a novel fully integrated 3-D magnetic sensor. This low-field sensor, based on buried silicon Hall devices, combines two vertical Hall devices for the planar sensitivity and novel horizontal Hall elements for the orthogonal sensitivity. The advantages of this sensor are its very low cross-sensitivity and its remarkably high long-term stability. The X and Y directions are used as high-precision angular-position measurements and the third direction helps to compensate for mechanical misalignment.

Fully integrated probe for proton nuclear magnetic resonance magnetometry

In this article, we present the first fully integrated nuclear magnetic resonance probe ever realized. Planar spiral coils, a radio-frequency preamplifier, a mixer, and an audio-frequency amplifier are integrated using a standard complementary metal–oxide–semiconductor technology on a single silicon chip of 10 mm2. A 1 mm3 solid sample of cis-polyisoprene, placed over one of the integrated coils, is used as resonating material. The realized integrated probe allows measurements of static magnetic fields from 0.7 to 7 T with a magnetic-field resolution better than 1 ppm/Hz1/2, an absolute accuracy better than 3 ppm, and a spatial resolution of about 1 mm.

A silicon blue/UV selective stripe-shaped photodiode

Abstract A novel silicon photodiode for the selective blue/ultraviolet (UV) light detection is presented. A stripe-shaped anode geometry is used to improve the UV-responsivity of photodiodes fabricated in CMOS processes by minimizing the dead layer area. The selectivity is achieved using a shallow active region, limited by a high potential barrier at a depth of 450 nm. The measured devices, realized in standard 0.5 μm CMOS technology, have maximum responsivity at λ =400 nm with a quantum efficiency of 53%. A ratio of the responsivities at 400 nm and 1 μm of 100 is achieved. In comparison to structures with traditional anodes, our stripe-shaped photodiode shows an increase of the UV responsivity by a factor 1.7, as predicted. The special anode geometry also improves the photodiode shunt resistance.