Jan Van der Spiegel

Flexible, foldable, actively multiplexed, high-density electrode array for mapping brain activity in vivo

Arrays of electrodes for recording and stimulating the brain are used throughout clinical medicine and basic neuroscience research, yet are unable to sample large areas of the brain while maintaining high spatial resolution because of the need to individually wire each passive sensor at the electrode-tissue interface. To overcome this constraint, we developed new devices that integrate ultrathin and flexible silicon nanomembrane transistors into the electrode array, enabling new dense arrays of thousands of amplified and multiplexed sensors that are connected using fewer wires. We used this system to record spatial properties of cat brain activity in vivo, including sleep spindles, single-trial visual evoked responses and electrographic seizures. We found that seizures may manifest as recurrent spiral waves that propagate in the neocortex. The developments reported here herald a new generation of diagnostic and therapeutic brain-machine interface devices.

Fabrication of a dual-tier thin film micropolarization array

A thin film polarization filter has been patterned and etched using reactive ion etching (RIE) in order to create 8 by 8 microns square periodic structures. The micropolarization filters retain the original extinction ratios of the unpatterned thin film. The measured extinction ratios on the micropolarization filters are approximately 1000 in the blue and green visible spectrum and approximately 100 in the red spectrum. Various gas combinations for RIE have been explored in order to determine the right concentration mix of CF(4) and O(2) that gives optimum etching rate, in terms of speed and under-etching. Theoretical explanation for the optimum etching rate has also been presented. In addition, anisotropic etching with 1 microm under cutting of a 10 microm thick film has been achieved. Experimental results for the patterned structures under polarized light are presented. The array of micropolarizers will be deposited on top of a custom made CMOS imaging sensor in order to compute the first three Stokes parameters in real time.

Tilted Pillars on Wrinkled Elastomers as a Reversibly Tunable Optical Window

We demonstrate the design and fabrication of tilted micropillar arrays on wrinkled elastomeric poly(dimethylsiloxane) as a reversibly switchable optical window. Upon re-stretching the as-prepared (opaque) film to the original pre-strain, the grating color is restored and ∼ 30% transmittance is recovered. Further stretching beyond the pre-strain makes the film more transparent. This process is fully reversible and repeatable for many cycles.

Dual-tier thin film polymer polarization imaging sensor

Traditional imaging systems capture and replicate the imaged environment in terms of color and intensity. One important property of light, which the human eye is blind to and is ignored by traditional imaging systems, is polarization. In this paper we present a novel, low power imaging sensor capable of recording the optical properties of partially linearly polarized light in real-time. The imaging sensor combines polymer polarization filters with a CMOS image sensor in order to compute the first three Stokes parameters at the focal plane. The imaging array contains 100 x 100 pixels and consumes 48 mW at 30 fps.

Multifrequency Pierce Oscillators Based on Piezoelectric AlN Contour-Mode MEMS Technology

This paper reports on the first demonstration of multifrequency (176-, 222-, 307-, and 482-MHz) oscillators based on the piezoelectric AlN contour-mode microelectromechanical systems technology. All the oscillators show phase noise values between -88 and -68 dBc/Hz at 1-kHz offset frequency from the carriers and phase noise floor values as low as -160 dBc/Hz at 1 MHz offset. The same Pierce circuit design is employed to sustain oscillations at the four different frequencies; on the other hand, the oscillator core consumes 10 mW. The AlN resonators are currently wire bonded to the integrated circuit realized in the AMIS 0.5-¿m 5-V complimentary metal-oxide-semiconductor process. Limits on phase noise and power consumption are discussed and compared with other competing technologies. This paper constitutes a substantial step forward toward the demonstration of a single-chip multifrequency reconfigurable timing solution that can be used in wireless communications and sensing applications.

Formation of epitaxial yttrium silicide on (111) silicon

The growth of epitaxial yttrium silicide on Si(111) in ultrahigh vacuum is studied. Resistivity, epitaxial quality, and pinhole coverages are studied as a function of annealing temperature for each growth method used. The best films result from the growth of a thin, 30–40‐A template layer which is annealed to 700 °C, followed by a thicker film growth by depositing additional Y onto the substrate heated high enough to induce silicide formation (∼300 °C). Annealing to 900 °C results in a Rutherford backscattering minimum channeling yield χmin ∼3%, which is the same order of epitaxial quality previously achieved by only Ni‐ and Co‐silicide films on silicon. Films grown without templates have larger pinhole sizes with pronounced features indicative of the hexagonal nature of these structures. The deposition of Y metal onto a substrate held at room temperature, followed by annealing to 900 °C results in the lowest resistivities (48 μΩ cm for 425‐A films), but with a highly dislocated film structure featuring 1...

Acoustic-phonetic features for the automatic classification of fricatives

In this article, the acoustic-phonetic characteristics of the American English fricative consonants are investigated from the automatic classification standpoint. The features studied in the literature are evaluated and new features are proposed. To test the value of the extracted features, a statistically guided, knowledge-based, acoustic-phonetic system for the automatic classification of fricatives in speaker-independent continuous speech is proposed. The system uses an auditory-based front-end processing system and incorporates new algorithms for the extraction and manipulation of the acoustic-phonetic features that proved to be rich in their information content. Classification experiments are performed using hard-decision algorithms on fricatives extracted from the TIMIT database continuous speech of 60 speakers (not used in the design/training process) from seven different dialects of American English. An accuracy of 93% is obtained for voicing detection, 91% for place of articulation detection, and 87% for the overall classification of fricatives.

Retinalike space variant CCD sensor

The retina is a smart sensor, but in the sense of intelligent design and not on-chip computing power. It uses a unique layout and elementary charge computing elements to implement in hardware a polar-exponential transform on visual data. The final chip includes a large section of photosites arranged in a circular pattern. Further, the pixels grow m size as radial distance increases. The retina also has a fovea (a high resolution area at the chips center) and the computational circuitry. The sensor works and will serve as the key component of a real-time imaging system.

Current Mode Image Sensor With Two Transistors per Pixel

A linear current mode active pixel sensor for low fixed-pattern noise imaging is presented. The photo pixel is composed of a photodiode, a reset transistor, and a transconductance amplifier transistor. The address switch transistor is placed outside the pixel. The increased linearity of the pixel current coupled with current mode difference double sampling greatly reduces spatial variations across the image sensor array. The fabricated image sensor is composed of an array of 50 × 128 pixels and consumes 5 mW at 30 fps. Column fixed pattern noise of 0.1% from the saturated current and signal to noise ratio of 43.3 dB is achieved.

Formation of epitaxial yttrium and erbium silicide on Si(111) in ultra-high vacuum

Abstract The growth of epitaxial yttrium and erbium silicide on Si(111) in ultra-high vacuum is studied. Resistivity, epitaxial quality, and pinhole distributions are studied as a function of annealing temperature. The best films result from the growth of a thin template layer ( 2− x to 900°C and ErSi 2− x to 850°C results in the lowest resistivities (48 μΩ cm for 425 A YSi 2− x and 30 μΩ cm for 200 A ErSi 2− x films). Furthermore, these films have Rutherford backscattering minimum channeling yields χ min ≈ 3% and 2% for Y- and Er-silicides,respectively. YSi 2− x appears to have a sharper interface with Si(111) than does ErSi 2− x from RBS, while pinhole sizes increase with annealing temperature for both silicides, with well-defined hexagonal features prevalent in the ErSi 2− x films only. These are perhaps indicative of the differences in lattice matching with Si(111) of the two silicides.