Thursday, November 18, 2010

IC Fabrication Process -1

The first step comprises of preparing Si or Ge wafer with desired purity level.

The processing characteristics and some material properties of silicon wafers depend on its orientation.The <111> planes have the highest density of atoms on the surface, so crystals grow most easily on these planes and oxidation occurs at a higher pace when compared to other crystal planes.Traditionally, bipolar devices are fabricated in <111> oriented crystals whereas <100> materials are preferred for MOS devices.

Electronic-grade silicon (EGS), a polycrystalline material of high purity, is the starting material for the preparation of single crystal silicon. EGS is made from metallurgical-grade silicon (MGS) which in turn is made from quartzite, which is a relatively pure form of sand.

CzochralskiCrystal Growth

The Czochralski(CZ) process, which accounts for 80% to 90% of worldwide silicon consumption, consists of dipping a small single-crystal seed into molten silicon and slowly withdrawing the seed while rotating it simultaneously.Impurities, both intentional and unintentional, are introduced into the silicon ingot. Intentional dopantsare mixed into the melt during crystal growth, while unintentional impurities originate from the crucible, ambient, etc.

Float-Zone Process
The float-zone process has some advantages over the Czochralski process for the growth of certain types of silicon crystals.The molten silicon in the float-zone apparatus is not contained in a crucible, and is thus not subject to the oxygen contamination present in CZ-Sicrystals.The float-zone process is also necessary to obtain crystals with a high resistivity(>> 25 W-cm)

Silicon, albeit brittle, is a hard material. The most suitable material for shaping and cutting silicon is industrial-grade diamond. Conversion of silicon ingots into polished wafers requires several machining, chemical, and polishing operations.

The wafer as cut varies enough in thickness to warrant an additional lapping operation that is performed under pressure using a mixture of Al2O3and glycerine. Subsequent chemical etching removes any remaining damaged and contaminated regions.Polishing is the final step. Its purpose is to provide a smooth, specular surface on which device features can be photo engraved.

Sinc Function

In mathematics, the sinc function, denoted by sinc(x) and sometimes as Sa(x), has two nearly equivalent definitions. In digital signal processing and information theory, the normalized sinc function is commonly defined by
\mathrm{sinc}(x) = \frac{\sin(\pi x)}{\pi x}.\,\!

It is qualified as normalized because its integral over all x is one. The Fourier transform of the normalized sinc function is the rectangular function with no scaling. This function is fundamental in the concept of reconstructing the original continuous bandlimited signal from uniformly spaced samples of that signal.

In mathematics, the historical unnormalized sinc function is defined by
\mathrm{sinc}(x) = \frac{\sin(x)}{x}.\,\!
The only difference between the two definitions is in the scaling of the independent variable (the x-axis) by a factor of π.

The normalized sinc function can be used as a nascent delta function, meaning that the following weak limit holds:
\lim_{a\rightarrow 0}\frac{1}{a}\textrm{sinc}(x/a)=\delta(x).
This is not an ordinary limit, since the left side does not converge.

Tuesday, November 16, 2010

Important Time Zones

1. New Delhi
Standard time zone:UTC/GMT +5:30 hours
No daylight saving time in 2010
Time zone abbreviation:IST - India Standard Time

2. Berlin
Standard time zone:UTC/GMT +1 hour
No daylight saving time at the moment
Time zone abbreviation:CET - Central European Time

3. Tashkent
Standard time zone:UTC/GMT +5 hours
No daylight saving time in 2010
Time zone abbreviation:UZT - Uzbekistan Time

4. Bangkok
Standard time zone:UTC/GMT +7 hours
No daylight saving time in 2010
Time zone abbreviation:ICT - Indochina Time

5. Rio De Janeiro
Standard time zone:UTC/GMT -3 hours
Daylight saving time:+1 hour
Current time zone offset:UTC/GMT -2 hours
Time zone abbreviation:BRST - Brasilia Summer Time

6. Asunción
Standard time zone:UTC/GMT -4 hours
Daylight saving time:+1 hour
Current time zone offset:UTC/GMT -3 hours
Time zone abbreviation:PYST - Paraguay Summer Time

7. Tokyo
Standard time zone:UTC/GMT +9 hours
No daylight saving time in 2010
Time zone abbreviation:JST - Japan Standard Time

8. Nairobi
Standard time zone:UTC/GMT +3 hours
No daylight saving time in 2010
Time zone abbreviation:EAT - Eastern Africa Time

9. Caracas
Standard time zone:UTC/GMT -4:30 hours
No daylight saving time in 2010
Time zone abbreviation:VET - Venezuelan Standard Time

10. New York
Standard time zone:UTC/GMT -5 hours
No daylight saving time at the moment
Time zone abbreviation:EST - Eastern Standard Time

11. Seattle
Standard time zone:UTC/GMT -8 hours
No daylight saving time at the moment
Time zone abbreviation:PST - Pacific Standard Time

Saturday, November 13, 2010


A thermocouple is a junction between two different metals that produces a voltage related to atemperature difference. Thermocouples are a widely used type of temperature sensor for measurement and control[1] and can also be used to convert heat into electric power. They are inexpensive[2] and interchangeable, are supplied fitted with standard connectors, and can measure a wide range of temperatures. The main limitation is accuracy: system errors of less than one degree Celsius (C) can be difficult to achieve.[3]

Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are used for different temperature ranges. Properties such as resistance to corrosion may also be important when choosing a type of thermocouple.

Thermocouples are suitable for measuring over a large temperature range, up to 2300 °C.Thermocouples are widely used in science and industry; applications include temperature measurement for kilnsgas turbine exhaust, diesel engines, and other industrial processes.

Pros and Cons

 -Low cost.
 -No moving parts, less likely to be broken.
 -Wide temperature range.
 -Reasonably short response time.
 -Reasonable repeatability and accuracy.
 -Sensitivity is low, usually 50 µV/°C (28 µV/°F) or less. Its low voltage output may be masked by noise. This problem can be improved, but not eliminated, by better signal filtering, shielding, and analog-to-digital (A/V) conversion.
 -Accuracy, usually no better than 0.5 °C (0.9°F), may not be high enough for some applications.
 -Requires a known temperature reference, usually 0°C (32°F) ice water. Modern thermocouples, on the other hand, rely on an electrically generated reference.
 -Nonlinearity could be bothersome. Fortunately, detail calibration curves for each wire material can usually be obtained from vendors.

Wheatstone Bridge

Wheatstone bridge is an electrical circuit invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. [1] It is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer.

The desired value of Rx is now known to be given as:
R_x = {{R_3 \cdot R_2}\over{R_1}}

Sunday, November 7, 2010

Understanding Cell



Cytology, more commonly known as cell biology, studies cell structure, cell composition, and the interaction of cells with other cells and the larger environment in which they exist.Microscopic examination can help identify different types of cells. In a simple test like a complete blood count, a laboratory can look at white blood cells and identify the presence of an infection, or it may examine a low level of certain types of red blood cells and diagnose anemia
The biochemical basis of cell differentiation is the synthesis by the cell of a particular set of proteins, carbohydrates, and lipids.The first cells presumably resembled prokaryotic cells in lacking nuclei and functional internal compartments, or organelles. These early cells were also anaerobic (not requiring oxygen), deriving their energy from the fermentation of organic molecules that had previously accumulated on the Earth over long periods of time. 


In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. 

The structure and location of chromosomes is one of the chief differences between the two basic types of cells—prokaryotic cells and eukaryotic cells. Among organisms with prokaryotic cells (i.e., bacteria and blue-green algae), chromosomes consist entirely of deoxyribonucleic acid (DNA). The single chromosome of a prokaryotic cell is not enclosed within a nuclear membrane. Among all other organisms (i.e., the eukaryotes), the chromosomes are contained in a membrane-bound cell nucleus. The chromosomes of a eukaryotic cell consist primarily of DNA attached to a protein core. They also contain ribonucleic acid (RNA). Among both prokaryotes and eukaryotes, the arrangement of components in the DNA molecules determines the genetic information.

Every species has a characteristic number of chromosomes (chromosome number). In species that reproduce asexually, the chromosome number is the same in all the cells of the organism. Among sexually reproducing organisms, the number of chromosomes in the body (somatic) cells is diploid (2n; a pair of each chromosome), twice the haploid (1n) number found in the sex cells, or gametes. The haploid number is produced during meiosis. During fertilization, two gametes combine to produce a zygote, a single cell with a diploid set of chromosomes.

Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (stationary phase) while the other (the mobile phase) moves in a definite direction.Affinity chromatography often utilizes a biomolecule's affinity for a metal. It is often used in biochemistry in the purification of proteins bound to tags.

Ion exchange chromatography uses ion exchange mechanism to separate analytes.Ion exchange chromatography uses a charged stationary phase to separate charged compounds including amino acids,peptides, and proteins.


The largest animal that ever lived is also currently living -- the blue whale.
Mitochondrial DNA is only inherited from our mother.
"DNA makes RNA, RNA makes protein, and proteins make us." Francis Crick 

Friday, November 5, 2010

General Awareness

1. Saccharimeter:

saccharimeter is an instrument for measuring the concentration of sugar solutions.
This is commonly achieved using a measurement of refractive index (refractometer) or the angle of rotation of polarization of optically active sugars (polarimeter).
Saccharimeters are used in food processing industries, brewing, and the distilled alcoholic drinks industry.

2, Ammeters
Zero-center ammeters are used for applications requiring current to be measured with both polarities, common in scientific and industrial equipment. Zero-center ammeters are also commonly placed in series with a battery.

3. Manometer
Static pressure is uniform in all directions, so pressure measurements are independent of direction in an immovable (static) fluid.

4. Barkometer
A barkometer is calibrated to test the strength of tanning liquors used in tanning leather.[10]

5. William Herschel

Herschel became most famous for the discovery of the planetUranus in addition to two of its major moons, Titania and Oberon. He also discovered two moons of Saturn and infrared radiation. Finally, Herschel is less known for the twenty-four symphonies that he composed.

6. Robert koch
He was awarded the Nobel Prize in Physiology or Medicine for his tuberculosis findings in 1905.The crater Koch on the Moon is named after him. The Robert Koch Prize and Medal were created to honour Microbiologists who make groundbreaking discoveries or who contribute to global health in a unique way. The now-defunct Robert Koch Hospital at Koch, Missouri (south of St. Louis, Missouri), was also named in his honor. 

7. Alexander Oparin
He was a Soviet biochemist notable for his contributions to the theory of the origin of life, and for his authorship of the book The Origin of Life. Oparin sometimes is called "Charles Darwin|Darwin" of the 20th century.Many of his early papers were on plant enzymes and their role inmetabolism.[3]He showed that many food-production processes are based on biocatalysis and developed the foundations for industrial biochemistry in the USSR.[2]

Rømer starts with an order of magnitude demonstration that the speed of light must be so large that it takes much less than one second to travel a distance equal to Earth's diameter. 
Rømer also invented the Meridian circle, the Altazimuth and the Passage InstrumentRømer also developed one of the first temperature scales.Fahrenheit visited him in 1708 and improved on the Rømer scale, the result being the familiar Fahrenheit temperature scale still in use today in a few countries.

9. Astrobiology
Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. Earth is the only known inhabited planet in the universe to date.Nucleic acids may not be the only biomolecules in theUniverse capable of coding for life.[1] Extremophiles (organisms able to survive in extreme environments) are a core research element for astrobiologists. The NASA Kepler mission, successfully launched in March 2009, searches for extrasolar planets.

10. Philology
Philology is the study of language in written historical sources, as such it is a combination ofliterary studieshistory and linguistics.[1]Another branch of philology, cognitive philology studies written and oral texts, considering them as results of human mental processes. Because of its focus on historical development (diachronic analysis), philology came to be used as a term contrasting with linguisticsLinguistics is the scientific[1][2] study of human language.