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Microchipsa simple introductionSecond EditionSitaramarao S. Yechuri, Ph.D.ISBN 0-9741037-1-3Library of Congress Control Number: 2004093110Printed June, 2004Copyright 2004 by Yechuri Software, Arlington, TX.All rights reserved. No part of this publication may be reproduced, stored in a retrieval system,or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording,or otherwise, without prior written permission of the publisher. Printed in the United States ofAmerica.IntroductionIntegrated circuit chips made of Silicon have undeniably transformed our world and the biggestchange happened in just 35 years. The rst Germanium (Ge) transistor was built in Bell Labora-tories in 1947 by Walter Brattain and John Bardeen. The rst integrated circuit was built at TexasInstruments in 1958 by Jack Kilby. Nowadays all micro-chips are made of Silicon (Si).No one can predict the future and mankind has developed many technologies that zzledout or just never became very popular. Some technologies developed slower than others. Twohugely important industries of our times, namely the automobile industry and the semiconductorindustry have displayed different behavior.Automobile technology started in 1889 and is still evolving slowly. It is an industry with ahuge inertia that limits how quickly it can evolve. It is capital intensive and labor intensive andnowadays the prot margin is not that high due to robust competition. And in some ways it hasnot changed that much.The efciency of todays cars are not more than double that of the cars of the 1930s and ourcars today still use gasoline and still use an overhead cam-shaft to regulate the valves. Cars havebecome lighter, but people still drive a 2000 lb car to transport a single 150 lb person. Top speedsfor the cars of the 1940s was easily a 100 mph, and even today cars are built to run at no morethan 100 mph and practical speeds on the roads do not exceed 70 mph.Semiconductors on the other hand grew very rapidly in the 1990s and matured very quicklyindeed. The metric used is the length of the gate of the transistors used. In 1965 Gordon Mooreof Intel corporation predicted that the transistor density would basically double every year andso far it has been quite accurate. In fact it is almost a business prediction as much as a technologyprediction in that consumers have grown to expect the new computers to become faster every fewmonths and they still expect to pay only as much as they did before. In fact it is common forconsumers to put off purchasing electronics until just before they need it because they believe thattomorrow everything will be a little cheaper and faster.Another important feature of the micro-chip industry is that in a sense it did accelerate its owngrowth. What I mean is this. Up to 1970 most technology was developed on pen and paper. It wasanalytical. It is a very, very sad fact that analytical techniques are virtually unused today except byvery few technical people. The pocket calculator was the rst step in increasing the speed of chipdesign because it allowed chip designers to calculate transistor sizes and bias points to severaldecimal places of accuracy instantly. The early TI programmable calculators had a slot throughwhich you passed a magnetic strip of paper containing instructions you had coded previously andthey were read in and the calculator was ready to perform a sequence of calculations rather thanjust one.Chip designers were initially circuit designers and did all their design work with pencil andpaper and a calculator. At that time most chips were analog in function. But by the 1990s com-puters started to take on the weight of chip design and chip designers became little more thanprogrammers. By then most chips were digital in nature. And this process started to feed on itselfiiii.e., the improvement in computer speed allowed better and faster chip design software which inturn allowed better and faster chips to be designed and so on.In a sense the chip shrink process was on a glide-path because the minimum feature size of themicro-chips was dictated by the wavelength of light used to dene them and chip manufacturingequipment manufacturers just used lower and lower wavelengths to dene the features and itseemed the juggernaut would never stop.But the juggernaut is slowing down because the wavelength of the light needed to dene thefeatures has become so small that the energy of the photons (which is inversely proportional tothe wavelength) is now that of an X-ray. At such a high energy there are few photon sensitivematerials which can respond to it.Another factor which is causing a problem is the gate oxide thickness which has already beenreduced to no more than ve layers of atoms. Besides these two factors the FETs made at verysmall dimensions are not delivering the behavior needed to properly design integrated circuits.At the time of this writing 0.09 is the cutting-edge of the semiconductor processes world-wide and it is this authors opinion that the 0.06 generation which we will attain by 2006 or asubsequent 0.05 generation may well be a stable point at which the industry starts to becomecommoditized and prices are driven to the minimum and when applications become the mainfocus. This happened with the automobile industry and it will probably happen with the chipindustry.Keep in mind that even well known industry experts dont agree on how much further siliconbased chips can be shrunk and many of these experts have a vested interest in persuading thepublic that newer, faster and cheaper technologies are just around the corner and that you shouldinvest your money in the leading semiconductor companies even at high P/E ratios. When youread about newer technologies, the key question you should ask is not whether they are feasiblebut whether they can be made cheaper than existing technology.My belief is that chips with many layers of circuitry stacked one on top of the other offers thekey to higher density. To make this a reality I believe that techniques that are additive like epitaxyor chemical vapor deposition need to become much more cost effective, which could happen if thevolume of usage were increased. They also can be done at lower temperatures which is necessaryto keep the lowest circuit levels functional and nally there needs to be a way to sandwich passiveheat sinks between the layers to suck the heat out because otherwise the middle levels will burnup.ivContents1 Passive circuits 11.1 The three passive lumped elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.3 Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1.4 Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Basic circuit laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.1 Ohms law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.2 Kirchoffs laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.3 Y transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.4 Mesh equations and node equations . . . . . . . . . . . . . . . . . . . . . . . 41.2.5 Thevenin and Norton equivalents . . . . . . . . . . . . . . . . . . . . . . . . . 51.2.6 Maximum power transfer theorem . . . . . . . . . . . . . . . . . . . . . . . . 51.2.7 Transient analysis using Laplace transforms . . . . . . . . . . . . . . . . . . . 62 Active devices - historical 72.1 Vacuum technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3 Triode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.4 Klystron tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.5 Read diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.6 Gunn diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Semiconductor theory 133.1 Wave particle duality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14