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Unit 4 Microelectronics,Passage A Introduction to Microelectronics Passage B The Simple Atom, Conductors, Insulators and Semiconductors Passage C Diode and Transistor,Passage A Introduction to Microelectronics The exploring of space and the development of earth satellites has increased the importance of reducing the size and weight of electronic circuits. Also, even though electricity flows quite rapidly in computers the time delay of the signal in the interconnections between electronic components is an important consideration. If the interconnections are reduced in size, a computer can perform operations at a faster speed. Microelectronics involves the miniaturization of regular electronic circuits. A complete electronic circuit, an operational amplifier for example, which contains large numbers of individual interconnected components, such as diodes resistors, transistors, etc. may be formed on a very small single substrate. The complete miniaturized circuit is then called an integrated circuit.,Integrated circuits are small, light, rugged, and reliable. They require less power and lower voltages than equivalent macroscopic circuits; consequently they operate at lower temperatures, and individual components may be close together without exceeding the operating temperature limit. Relatively little stray capacitance and short time delays are produced because of the short interconnections between the individual components in IC. Maintenance is simplified because if a component of the IC fails the complete IC is usually replaced. Mass production techniques of plane technology have reduced the cost of many IC so that they are almost as inexpensive as a single transistor. Eventually most conventional circuits will be replaced by IC.,There are two types of basic integrated circuit: monolithic integrated circuit and the thin or thick film. Monolithic IC are constructed in a single substrate of single crystal semiconductor, usually silicon. Thin or thick films IC are formed on the surface of an insulating material such as glass or a ceramic. Hybrid IC contains more than a single substrate, the term hybrid is also applied to combinations of monolithic and thin or thick film IC.,Integrated circuits are also classified according to their functions. Digital or logical IC are used as switches, they are either on or off. In computers the on and off states correspond to 0 or 1. Other IC is called linear or analog IC.1 Integrated circuits can be produced using either bipolar or unique polar transistors. Field effect transistors (FET) have a advantages over bipolar transistors in many cases however. They are relatively high-impedance devices, with a corresponding reduction in current and power dissipation, and yet have high power gain. The reduction in power dissipation is particularly important where a complex circuit is to be concentrated into a small space. The problem of extracting the heat generated in the circuit may then be a difficult one.2 The form of construction of the FET, and particularly the MOSFET, also lends itself well to integrated circuit fabrication, and enables resistors and capacitors to be included readily in the integrated circuit.,Most electronic circuits are composed of active devices, e.g. transistors and diodes, together with resistors (for bias, collector load, impedance transformation, etc.) and capacitors (e.g. for coupling ac signals while blocking dc supplies). Each of these elements can be produced in a form suitable for integrated circuit inclusion within limitations, e.g. capacitance values must not be too large. Some elements are difficult to produce in a suitable form, e.g. inductive elements, or large capacitors. Usually some alternative circuit form can be devised that dispenses with the requirement. Otherwise they must be included as an external lumped element.,Notes 1 Intergraded circuits are also classified according to their functions. Digital or logical IC are used as switches, they are either on or off. In computers the on and off states correspond to 0 or 1.Other IC is called linear or analog IC. 也可根据其功能不同对集成电路进行分类。 数字IC(也称为逻辑IC)通常用作开关, 表示接通或关断。 在计算机中, 接通和关断状态分别对应“0”或“1”。 另一种IC被称为线性或模拟IC。 either.or.表示两者择一, 在文中译为“要么要么”。 ,2 The reduction in power dissipation is particularly important where a complex circuit is to be concentrated into a small space. The problem of extracting the heat generated in the circuit may then be a difficult one. 减小功率损耗是非常重要的, 其方法是将一个复杂的电子线路集成为一小块。 这使得释放电路工作时产生的热量变成一个难题。 The problem of.may then be a difficult one. 文中的one表示强调这个问题, 这种句式在科技英语中常被使用。 extracting the heat 为释放热量的意思, extract的本意为“抽出, 剥离”。 在电子线路中, 器件工作均会产生热量, 如果不能及时散热, 器件就不能稳定工作。 ,Exercises 1. Please translate the following sentences into English, using infinite verb on the parts underlined. (1) 为了测量电阻, 我们使用单位“欧姆”。 (2) 重要的是要应用这些定律。 (3) 这种装置能用来测量电流、 电压、 电阻。 (4) 我们想要求这个电路中的电流。 (5) 无线电波的用途之一是发送信息。 (6) 在这种情况下该物体被说成带电了。 (7) 我们感到理解这个概念很困难。 ,2. Please translate the following sentences into Chinese. (1) It is assumed that the reader has a general knowledge of circuit theory. (2) Which of these methods is determine Req depends upon which is the easiest in any given situation. (3) It is an experimental fact that an electric field is established in a conducting rod when there is a temperature difference between its ends. (4) That this condition is sufficient is obvious.,(5) It can be shown that any rational function of sin x and cos x can be integrated. (6) A major advantage of this device is that it operates continuously. (7) In this chapter we shall determine which load receives the maximum power for a given practical voltage source.,Passage B The Simple Atom, Conductors, Insulators and Semiconductors The Simple Atom The materials that make up our universe are composed of over one hundred basic and individual types of matter called elements. Ninety-two of these elements occur naturally and the remainders are man-made. Each element has a separate identify of its own, that is, no two elements have the same physical and chemical properties, nor can an element be subdivided by ordinary physical and chemical means into simple elements.1 Examples of elements are gold, mercury and oxygen.,Elements contain smaller particles called atoms. In any one element the atoms are identical in structure. The difference between any two elements such as gold and mercury is in their atomic structures. They have in common, however, a relatively heavy inner core called a nucleus surrounded by one or more extremely light particles of matter called electrons. The simplest nucleus is a mass of matter about 2,000 times the weight of an electron, and is called a proton. More complex nuclei contain various combinations of protons and neutrons. A neutron is a proton combined with an electron and is electronically neutral.,Electrons whirl around nuclei in much the same manner that the planets of our solar system travel around the sun. The difference between an atom of one element and that of another is in the number of protons and neutrons contained in the nucleus.2 All the elements in the universe, and therefore all matter, is composed of protons, neutrons, and electrons. There must be force of attraction between a nucleus and the electrons surrounding it, otherwise the electrons would fly off into space, in order to understand its nature, we find it helpful to call this force a charge. The charge of the nucleus is defined as positive, and the opposite charge of the electron, negative. In view of the fact that opposites attract, the force between the nucleus and the rotating electron around it prevents the electron from flying off into space.,An atom, which has all of its orbital (rotating) electrons has as many positive charges and therefore the net charge is zero. When an atom loses an electron the balance of charge is disturbed and the atom becomes positively charged. In this condition, the atom is called a positive ion. In comparison, when an atom acquires an electron, the balance of charges is again disturbed and the atom becomes negatively charged, such an atom is referred to as a negative ion.,Conductors, Insulators and Semiconductors Any substance, which allows electrons to flow freely through its structure is called a conductor. In general, metals are good conductors. A definite relationship exists between good conductors and their atomic structures. In good conductors, the outer-ring electrons, which are also called valence electrons, may be released from their orbits with relative ease. Atom with 1, 2 and 3 outer ring electrons, and therefore most metals are good conductors.,Substance, which prevent the passage of electrons through their structures are called insulators. Insulators have very few easily removed electrons in their outer rings. There are no perfect insulators: first, because of the presence of impurities (foreign materials) which can never be entirely removed; and second, because even a small amount of heat will cause a certain number of valence electrons to be freed from their atoms. Insulators generally have very stable atomic structures, of which the 4-electron outer-ring structure is typical. In such a structure, there is an absence of easily removed electrons. Example of good insulators are certain compounds of carbon (a basic ingredient of rubber ) and diamond, which has a similar atomic structure.,Semiconductors are a group of materials, which conduct electrons poorly and therefore cannot properly be classified either as conductors or insulators. Generally, semiconductors differ from insulators in that their outer-ring electrons can detach themselves from their orbits more easily than in insulators. Typical semiconductors materials are germanium and silicon. Impurities may be added to pure semiconductors. This results in semiconductor materials, which may either have an excess of free electrons or a deficiency of orbital electrons. When an excess of electrons is present we call the material N-type; when lack of orbital electrons occurs, we call the material P-type. Both N-type and P-type semiconductors are made by treated materials. such as germanium and silicon with impurities such as arsenic and indium. The addition of impurities to semiconductors is called doping.,Notes 1 Each element has a separate identity of its own, that is, no two elements have the same physical and chemical properties, nor can an element be subdivided by ordinary physical and chemical means into simple elements. 每一种元素均有它自己的标识, 也就是说, 没有两个元素具有相同的物理和化学特性, 一种元素也不能以普通的物理或化学方法被分为两种简单的元素。 that is是插入语。 nor 也不, 提到句首使用时, 句子要倒装, 表示强调。 ,2 Eletrons whirl around nuclei in much the same manner that the planets of our solar system travel around the sun. The difference between an atom of one element and that of another is in the number of protons and neutrons contained in the nucleus. 电子围绕原子核旋转, 其方式类似于太阳系中行星围绕太阳旋转。 一种元素的原子和另一种元素的原子的差别在于其原子核中的质子数和中子数。 in much the same manner that 中, in.manner意为“以的方式”, that是manner的定语从句。 ,3 Both N-type and P-type semiconductors are made by treated materials, such as germanium and silicon with impurities such as arsenic and indium. N型半导体和P型半导体是利用杂质掺入纯净半导体而形成的, 如将杂质砷和铟掺入锗和硅中。 are made by treated material, treat原意为对峙, treated materials指前文将杂质掺入纯净半导体的过程。 ,Exercises 1. True/False. (1) The materials that make up our universe are atoms.( ) (2) Generally we distinguish the elements by their atomic structures. Each atom has a unique identify. ( ) (3) The atom is always composed of proton, neutrons and electrons. ( ) (4) When the temperature is high, an electron can attract amount heat and then fly off into space. ( ) (5) The semiconductor can permit the current through their body if some condition is supplied. ( ),6.If you put impurities adding to pure semiconductors, this results in semiconductor materials, which only have an excess of free electrons. ( ) 7. When an excess of electrons is present, we call the material P-type; when lack of orbitalelectrons occurs, we call the material N-type. ( ) 8. Both N-type and P-type semiconductors are made by treated materials. such as germanium and silicon with impurities such as arsenic and indium. ( ) 9. The course of addition of impurities to semiconductors is called doping. ( ),2. Translate the following sentences into English. (1) 工科学生应该知道如何使用计算机。 (2) 物体做功的能力被称为能量。 (3) 重要的是我们要把理论应用于实践。 (4) 计算在这个电路中流动的电流密度是可能的。 (5) 这些是常用的设备。 (6) 电压等取决于电路中的电阻以及所加的电压。 ,3. Translate the following sentences into Chinese. (1) These capacitors are commonly used where change in capacitance is necessary. (2) The advent of electronics is reckoned from the discovery that the current in a vacuum diode can be controlled by introducing a third electrode. (3) The concept of work is so important that it will bear further discussion. (4) Just as good electrical conductors are also good conductors of heat, poor electrical conductors are also poor thermal conductors.,(5) By the use of electrical insulators, electrical currents can be confined to well-designed paths in good electrical conductors, while it is impossible to confine heat currents to a comparable extent. (6) The statement that a man weighs 160 pounds is equivalent to a statement that he is attracted by the earth with a force of 160 pounds.,Passage C Diode and Transistor The Basic Crystal Junction (or Diode) When a free electron meets a moving hole in a semiconductor material, the electron occupies the free space and a positive or negative charge no longer exists; that is, the charge is neutralized. When a P-type and a N-type crystal are joined to make a single semiconductor, as shown in Figure 9.1, current will flow in one direction only. As an example, when a power source is connected to the semiconductor as shown in Figure 9.2, the semiconductor is said to be forward biased.,Figure4.1 The basic crystal junction,Figure4.2 Forward biased connection in,The holes will be repelled toward the junction by the positively charged battery terminal, whereas the electrons are pushed toward the junction by the batterys negative terminal. At the junction, the electrons combine with the hole. Electrons enter the semiconductor at the N terminal to replace the electrons that have combined with the holes. Likewise, electrons leave the P terminal by attraction of positive voltage and create new holes. This movement of electrons, from the negative voltage source through the junction and from the positive terminal of semiconductor to positive voltage source, creates a current flow. Thus current will flow in a semiconductor when the semiconductor is forward biased.,When the polarity of the power source is reversed, the semiconductor is said to be reverse biased. The holes are moved away from the junction by the negative voltage, whereas the electrons are draw from the junction by the positive voltage. Thus there is little or no combining of electrons and holes at the junction, and no current will flow. In practical terms, there will always be a few electrons and holes near the junction, allowing a very small current to pass. This small current is known as leakage current and is usually in the order of a few microamperes (or possibly pico amperes).,When P-type and N-type regions are formed in same crystal, the semiconductor is known as a diode or rectifier. The boundary between the two regions is termed a junction. The P-region terminal is called the anode, whereas the N-region terminal is called the cathode. Usually, when such semiconductors are used with signals, the semiconductors are called diodes or signal diodes. When the device is used for conversion of alternating current (ac) to direct current (dc), the semiconductor is called a rectifier.,Basic Two-junction or Bipolar Transistor Like a diode, a transistor can be used to prevent (or limit) the flow of current in one direction, The prime use for a transistor, however, is to control the amount of current in a circuit. This is done by adding a second junction to the basic diode junction, discussed in the above section. For this reason, such transistors are called two-junction transistors or, possibly, bipolar transistors. The author prefers the former term but recognizes that the latter term is also in common use.,There are two possible arrangements for the two-junction in transistors: NPN, where a positive semiconductor material (holes) is placed between two negative semiconductor materials (electrons), and PNP, where the negative material (electrons) is placed between two positive materials (holes). With either junction arrangement, the basic two-junction transistor will have three elements. These elements, show in Figure9.3 as an NPN arrangement, are the emitter, which emits electrons; the collector, which collects electrons; and a base, which controls the flow of electrons by controlling the charge concentration at the two-junctions on either side of the base.,Figure4.3 NPN and PNP two-junction transistor arrangements,Figure9.4 shows how two junction transistor operates in its basic circuit. As shown, the emitter-base junction will pass current easily because the junction is forward biased. The collector-base junction will not pass current (except for a small leakage current) since the junction is reverse biased. (The term back is often used in place of reverse bias.),Figure4.4 Basic two-junction transistor bias circuit,It should be noted that the polarities of bias voltage for an NPN transistor differ from those of a PNP transistor; however, the net results are the same. For example, as shown in Figure9.4, the emitter is negative with respect to the base (NPN) to produce a forward bias. In Figure9.4, the emitter is positive with respect to base (PNP) to produce the same forward bias. Similarly, the collector has a reverse bias for both NPN and PNP, even though the polarities are revered. Also, it should be noted that for normal operation an NPN has its base biased positively with respect to its emitter. Conversely, a PNP base is negative with respect to its emitter.,(a) Basic two-junction transistor operation. During normal operation of a two-junction transistor, current will flow between emitter and base and between emitter and collector but not between collector and base. Most of the current flows between emitter and collector, because of the large voltage difference existing between these elements (the sum of the emitter-base voltage and the collector-base voltage). This produces a large number of charge carriers (positive holes in a PNP or negative electrons in an NPN) that diffuse through this base region when passing from emitter to collector (or vice versa). Few of these charge carriers combine with the charge (positive in NPN, negative PNP) in the base.,More charge carriers will be pulled out of the emitter and made available for the collector if the base-emitter current is increased. This can be accomplished by masking the base more negative in a PNP transistor or by making the base more positive in an NPN transistor. If the base-emitter voltage is decreased, less charge carriers will be pulled form the emitter and less emitter-collector current will flow.,Since very little voltage (approximately 0.2V for germanium and 0.5V for silicon) is required to produce a large current flow in the emitter, input power to a transistor is low. Most of the emitter current flows in the collector circuit, where the voltage is made much larger. As a result, a relatively large amount of power can be controlled in an external load (connected in series with the collector circuit) by a small amount of power in the emitter circuit. The power gain of a transistor (the ratio of output to power input) can be 40,000 or higher in some applications.,(b) Basic NPN transistor operation. In an NPN transistor, the base-emitter forward bias causes electrons from the emitter to move into the base, as shown in Figure9.5. Electrons flow through the thin base into the collector region, with only about 10% of the
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