First direct measurement of brain signals, from live
04/01/2003
Researchers at Infineon Technologies in Munich, Germany, in cooperation with the Max Planck Institute of Biochemistry, have directly connected a new biosensor IC to living nerve cells in snail brains. These researchers have read, for the first time, live electrical signals produced by brain cells.
This work was described at the recent 2003 International Solid State Circuits Conference. Dubbed "Neuro-Chip," the vision is that the new IC will allow researchers to gain new insights into the biologic function of neurons, nerve tissue, and organic neural networks.
For example, in the field of drug development, Neuro-Chip ultimately will enable tests of new pharmaceutical compounds on living neurons, contributing to greater efficiency and productivity in research.
The 5 ¥ 6mm Neuro-Chip includes a 128 ¥ 128 array of capacitive sensors in 1mm2. Below each sensor is a circuit that amplifies and processes the extremely weak signals of neurons (i.e., 100µV–5 mV peak-to-peak); the sensor array presents more than 32 million information bytes/sec. Roland Thewes, a senior director within the Corporate Research Center at Infineon, says, "When you look at the signal-to-noise ratio of this chip, it operates close to elementary physical limits."
The chip is based on a standard CMOS technology extended with additional proprietary process steps to realize the capacitive sensors array.
In use, individual neurons are placed into a nutrient solution above the sensor array (each nerve cell covers at least one sensor). The solution keeps neurons alive and allows for reconstruction of nerve tissue.
Compared to classical methods of research — in which neurons are damaged in the preparation of study samples — undisturbed observation of nerve tissue over a period of several weeks offers scientists continuous insight into the functionality of how the nervous system and brain learns, processes, and stores its learning.
 Infineon's new Neuro-Chip connected to living snail brains. (Source: Infineon Technologies, Max Planck Institute) |
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The Neuro-Chip's sensor density is ~300¥ today's common methods for studying neurons, which use glass substrates with vapor-deposited metallic lanes to contact the neuron. Each sensor on the chip is separated by 8µm (a typical neuron is 10–50µm).
Instead of sequentially checking every single neuron, Neuro-Chip surveys several neurons at the same time, producing more statistically relevant data. Also, Neuro-Chip enables recording of the operating sequence of electrical activity within nerve tissue over a defined time.
Every second, Neuro-Chip can record more than 2000 single values from each of its 16,384 sensors. The data can then be transformed into a color picture for visual analysis.—P.B.
Getting the shake out of interferometry
Scientists at Nano-Or Technologies (Lod, Israel) have come up with a combination of interferometry and optical digital imaging on a white light microscope that gives straightforward nondestructive wide-area 3D measurements with nanometer vertical (i.e., z-axis) and micron-range horizontal resolutions. One of the breakthroughs of the new method is its immunity to vibration because it takes the reference beam out of interferometry.
 A MEMS cantilever measured by the 3DScope2000, showing an upward curvature in the range of nanometers along 200µm. |
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Conventionally, interferometry has shown superior resolution for z-axis metrology in the laboratory. Its classic limitations include vibration sensitivity; and operating complexity, keeping it out of more routine production applications.
In its tabletop form, the new metrology instrument looks and operates much like a conventional white-light microscope. All microscope accessories (i.e., objectives, illumination modes, visualizations, etc.) are available. The added capability is a sensor, looking like, and performing in a similar way to, a CCD camera, allowing 3D topometry measurements.
Briefly explained, the microscope's partially coherent light illuminates the sample to be measured at any "what you see is what you get" magnification. Without a reference beam, vibration, turbulence, or dust does not change the optical path and does not degrade the measurement accuracy. The resulting monochrome CCD image, "grabbed" via a proprietary optical scheme, is manipulated electronically with Nano-Or Technologies' algorithms and software. What results is a computer matrix where each element of the matrix is a pixel in the field of view; each pixel contains height information for that particular point in the optical plane. Then, this "grabbed" information is used to construct a 3D map.
Nano-Or Technologies CEO, David Banitt, explains, "From these intensity-only images, the reflected wavefront from the object under inspection is fully analyzed for phase and amplitude data by our algorithms, modeling the optical system and the optical manipulation. The result of this analysis is the object's surface topography and reflectivity in the entire field of view, obtained with no scanning in any axis."
Once the 3D measurement is complete, an operator can perform a variety of data analysis and archiving functions, including 3D viewing, zooming in and out, cross-sectioning, and statistical analysis. Banitt sees potentially broad applications for this new technology. Examples include:
- silicon and compound IC manufacturing, including wafer surface, photoresist, and etch and lift-off inspection;
- MEMS z-axis movements and mapping (see figure on p. 22);
- BioMEMS cell response characterization;
- photonics components inspection and assembly alignment;
- flat panel display manufacturing, including surface planarity and defect characterization; and
- data storage media and read-write head inspection.—P.B.
8-in. dia. single-crystal BaF will cut stepper cost
New technology from Tokuyama Corp. (Tokyo) may reduce the cost of steppers by 20 to 30%. Tokuyama has developed a way to manufacture >8-in. dia. single-crystal barium fluoride (BaF).
This development will simplify production of compensation lenses of next-generation steppers to help focus the light when transferring circuit patterns to wafers. Currently, calcium floride (CaF) is used for that purpose.
Prof. Tsuguo Fukuda of the Tohoku U. Institute of Multidisciplinary Research for Advanced Materials guided Tokuyama on development of the new technology. Prof. Fukuda had previously helped Tokuyama develop a production process for CaF crystals. Tokuyama aims to develop a business to sell the BaF crystals as a lens material for steppers in one to two years.—K.F.
"Ohmi" plasma enables oxide growth at <400°C
Tokyo Electron Limited (TEL, Tokyo, Japan) has introduced a high-volume production system (the Trias SPA, a 200/300mm bridge tool) that uses a unique high-speed oxidation process originally developed by Professor Tadahiro Ohmi at Tohoku University.
The system is based on Ohmi's radial line slot antenna (RLSA) technology, a microwave-generated plasma. TEL engineers have spent years — including trial production applications for logic ICs in 2002 — developing this concept into its proprietary slot plane antenna (SPA) technology.
The resulting plasma has both a high density and a low electron temperature, so it generates high concentrations of oxygen radicals that grow high-quality oxidized films at temperatures <400°C, thus helping to reduce the total thermal budget used to fabricate leading-edge logic and DRAM devices at ≤65nm processing.
 Improvements in a) leakage current and b) Qbd with RLSA oxygen plasma treatment of CVD SiO2. |
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Sufficiently reducing heat-treatment temperatures associated with conventional thermally oxidized films has been a significant limitation, particulary when trying to grow reliable tunnel oxides for flash memories.
Part of the success at TEL has been developing an increase in radical density by supporting high power in the antenna and a portion of the process chamber. This enables high-quality films between 30 and 150Å on 200mm and 300mm wafers. Because the oxide films are more reliable than conventional thermally oxidized films (see figure), this process lends itself to tunnel oxide applications in flash memory.
The new process also is not dependent on crystal orientation, making it possible to apply it aggressively to devices where corner oxidation in shallow trench isolation schemes has been problematic. The low-temperature process technology enables excellent oxidation processes with minimal gate "bird's beak" and less WO3 sublimation in selective oxidation processes for poly-metal gates.—P.B.