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9.9 Option- The Age of Silicon: 1. Electronics, silica, the microchip and society

Syllabus reference (October 2002 version)
1. Electronics has undergone rapid development due to greater knowledge of the properties of materials and increasingly complex manufacturing techniques	Students learn to: identify that early computers each employed hundreds of thousands of single transistors explain that the invention of the integrated circuit using a silicon chip was related to the need to develop lightweight computers and compact guidance systems explain the impact of the development of the silicon chip on the development of electronics outline the similarities and differences between an integrated circuit and a transistor	Students: identify data sources, gather, process and analyse information to outline the rapid development of electronics and, using examples, relate this to the impact of electronics on society gather secondary information to identify the desirable optical properties of silica, including: refractive index ability to form fibres optical non-linearity

Extract from Physics Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.

[Edit: 2 July 09]

Prior knowledge: Preliminary modules: 8.2 (particularly part 5), 8.3 and HSC module 9.4, particularly part 3.

NOTE that past HSC papers have asked questions in this module that require you to use information from the HSC core module 9.4: From ideas to implementation in particular section 3 about transistors. Questions have assumed that you will know transistor and diode structure, function and principles of operation as well as how environmental factors, such as light and heat, impact on their electrical properties when they are used as transducers in circuits.

identify data sources, gather, process and analyse information to outline the rapid development of electronics and, using examples, relate this to the impact of electronics on society

Locate reliable, authoritative and recent sources that fill out to your satisfaction the story of the development of electronics. The bare bones of that story are provided below, but remember that it is only the syllabus point details that will be examined.
Sources you might access include:
- KIDS.NET.AU is the site of an interactive encyclopedia.
- The Nobel prize site has a history of semiconductors and vacuum tubes (thermionic emission) in its Educational section.
- The US Public Broadcasting Service provides some background information on the invention of transistors and integrated circuits.
- Jack Kilby (Texas Instruments) and Robert Noyce (Fairchild) are both credited with the discovery of the integrated circuit at the end of the 1950s.
- Intel is a company that manufactures ICs and they have information modules on their website about the electronics that drive today’s modern communication systems. Their online exhibit, From Sand to Circuits tells how Intel makes integrated circuit chips.

Background

To tell the story of electronics from the mid-twentieth century to the present time, you will need to know the physical structure and operating principles for the following devices:

thermionic valves
diodes
transistors
integrated circuits (ICs)
active and passive transducers
the difference between linear and non-linear devices
the similarities and differences between analogue and digital signals
systems for handling analogue and digital signals.

Some of that information can be found in HSC module 9.4, From ideas to implementation, in section 3 about semiconductors and transistors.

The key phases in the story of electronics are related to:

the thermionic valve
the transistor and its successor, the integrated circuit
the replacement of analogue with digital coding of information.

You should identify the key events and the time span when each was/is the dominant technology and provide a summary of significant refinements made and their advantages and disadvantages. Their disadvantages will assist you to understand why they were replaced with the next technology…and thus provide the beginnings of a list of advantages for the succeeding technology. Relevant features of each technology are outlined in the following snapshots about the thermionic valve, transistor and IC.

The thermionic valve is a relatively large, evacuated glass tube containing metal electrodes in a carefully organised but delicate structure. To do useful things, a valve needs external components such as capacitors, resistors and inductors and two power supplies. One is a low voltage, high current supply to produce the heat for thermionic emission of electrons (5 -15 volts). The other is a high voltage, low current supply to control the movement of electrons in the valve (100+ volts). An individual valve cannot be reduced in size much below half of an index finger on an adult hand. Useful equipment (radio, tape recorders, amplifiers and computers) requires multiple valves and related circuits containing large resistors, capacitors and inductors. The components need to be well spaced to allow for heat dissipation and to ensure that the high operating voltages do not cause short-circuits. Thus valve-based electronic equipment takes up a lot of space, is relatively heavy and needs to be kept in situ for long-term, reliable operation.

Transistors are relatively small, solid state devices (packaged into about 5 mm³ for low power applications) and physically robust. They do not require high voltages or currents and thus produce little heat. Initially they were made from a Germanium base, but Silicon became the preferred base because it could better handle higher currents and consequent higher temperatures than Germanium. Transistors, like valves, require external resistors, capacitors and inductors in their circuits to perform useful tasks. In low power applications, the size of resistors and capacitors can be reduced (less heat is produced to be dissipated) and they can be packed closer together in circuits without overheating or risking a short-circuit. The use of printed circuit boards and automated soldering processes (to fix all the components to a circuit board without human intervention) means that the same functionality as valve based electronics can be provided at a fraction of the cost (both in terms of material and labour) and in a greatly reduced package size. Transistor based equipment uses much less energy, is truly portable (lighter and smaller in size), more reliable (not so prone to physical damage) and can do much more (size for size) than valve based electronics. Battery technology was sufficiently advanced to provide practical amounts of energy to run transistorised equipment at a reasonable cost.

The first integrated circuits (ICs) contained a few transistors, resistors and capacitors all fabricated on what started out as a single, very pure, wafer of silicon crystal. Today, a single silicon crystal can have up to 10⁸+ transistors and related resistors and capacitors (as well as other devices and circuitry) all fitted onto an area covered by a five cent piece. Manufacture of ICs today is very complex and requires highly advanced technology to:

produce ultra clean environments
maintain high vacuum spaces where very small doses of metal vapour can be delivered to precisely identified regions of the substrate crystal
provide very precise measurements down to 10^-9 m (nanometers)
refine very pure sources of rare metal elements
support laser etching tools and computer-aided design.

These latest ICs, when compared to earlier ICs:

require little electrical energy to operate
are very robust
are extraordinarily fast
are relatively cheap to produce
are versatile
have massive calculating capacity.

It is interesting to note the social forces that drove the development of electronics from the 1940s and it’s growing impact on our daily lives.

The main impetus for the development of electronics from the mid-twentieth century was military conflict, eg World War 2, the Korean War and the Cold War. The need for better electronics to support the development of missile guidance and control systems and the space race to the moon led to the development and production of the first ICs in the US by the early 1960s.
Since the collapse of the Soviet Union and the end of the Cold War (by 1990), commercial and military interests have continued to fund research and development of bigger, more powerful and faster silicon-based very large scale integrated (VLSI) and ultra large scale integrated (ULSI) circuits.

NOTE: The above information about social forces is interesting but should not be included in an answer in the HSC.
Both military and commercial interests continue to build sophisticated global communication networks. These networks utilise computers, massive data storage banks, satellites, very high frequency radio (microwave) links on the ground and optical fibre networks (which are rapidly replacing copper wire-based networks) in the ground and under oceans to transfer digitised data around the Earth.
Faster and faster circuits are needed in the computers that manage the growing volume of data being moved around those networks. To achieve higher speeds, silicon-based ICs will need to be replaced soon (this will be explained in later material for this module).

After you have gathered and analysed the information you need to use the examples you have found to relate this to the impact of electronics on society.

identify that early computers each employed hundreds of thousands of single transistors

The first transistor based computers appeared in the second half of the 1950s and replaced those with valves. Transistors replaced valves because they took up less space (more transistors per unit area could be included in a computer than valves), used much less power and were more reliable. Large numbers of transistors were needed to perform the operations required to make computers practical tools.

explain that the invention of the integrated circuit using a silicon chip was related to the need to develop lightweight computers and compact guidance systems

Transistors were replaced by ICs in the late 1960s to make minicomputers. The first desktop or personal computer was the Altair 8800 produced for the mass market by Micro Instrumentation Telemetry Systems (MITS) in December 1974. Different integrated circuits to perform a variety of different functions were developed. By packaging a number of different integrated circuits into a single package, a set of useful functions could be achieved. This was the way the 8080 8-bit microprocessor that was made by Intel and then used by MITS in the Altair. In this way useful computing power was achieved as was miniaturisation, thus paving the way for portable computers and effective and practical missile guidance systems.

outline the similarities and differences between an integrated circuit and a transistor

Similarities
- Both use pure silicon as the starting point for their manufacture.
- Both are encased in a protective, heat dissipating electrical insulator.
- Both need to have conductors attached to the internal devices that pass through the casing for attachment to external circuits
- Both use low voltage direct current energy supplies.
Differences
- An IC contains the resistors and capacitors needed to make the transistors work as required as part of its internal structure (hence the term integrated circuits).
- An IC can have millions of transistors located on the same piece of silicon.
- An IC can perform much faster the same task as a separate transistor equivalent circuit.
- An IC is inherently more reliable than a separate transistor equivalent circuit.
- An IC is a much more efficient user of its externally supplied electrical energy than a separate transistor equivalent circuit.

explain the impact of the development of the silicon chip on the development of electronics

The impact of the silicon chip on the development of electronics can be demonstrated by refering to the differences between separate transistors and ICs. The use of ICs has enabled computers to become portable (laptops and notebooks); telephones once connected to a fixed network can become mobile; and, once separate devices are now available in a single package (convergence). By taking once separate ICs performing different functions and combining them into one package, we now have home entertainment systems (multimedia players, Sony Playstation and X Box) that provide video, TV and games capability along with related stereo or surround sound. Mobile phones can be purchased that are personal digital organisers (PDAs), computers and digital cameras that can capture and store single and video images for later sending to another phone or computer as needed..

gather secondary information to identify the desirable optical properties of silica, including: refractive index, ability to form fibres and optical non-linearity

The syllabus itself defines optical fibres (see p. 85) as:

Consisting of a core where light rays travel and the cladding which is made of a similar material with a slightly lower refractive index to cause total internal reflection. Two types of material are used to manufacture fibres – glass (silica) and plastic.
Try these sources below and organise the information collected in a way that is accessible to you (such as in a table) and helps you to understand why silica (pure glass) is used to make optical fibres.
- How stuff works has a series of pages that contain information relevant to the topic and a collection of other sites you can go to for more information.
- The following site explains how optical fibres are made Network Cabling Help, UK.
  
  The information you gather should support the outline provided below:
Glass has the same refractive index throughout. Light can be transmitted down a glass fibre using the property of total internal reflection. A ray of light moves through that glass in a straight line until it hits the boundary between the glass and another medium. If a light ray enters the glass fibre almost perpendicular to the end of the fibre, it will be totally internally reflected from the internal boundary of the glass and the other medium to eventually emerge from the other end of the fibre, even if the fibre turns back on itself.
Scientists have discovered that you can improve the efficiency of this internal reflection process if the refractive index (RI) of the glass is highest at its core and progressively reduced as you move to the outer edge. This change in RI as you move from the fibre core to the outer cladding (as it is called) can be achieved by deliberately introducing chemicals, such as germanium and boron, into ultra-pure glass in a process called doping.
A lump of doped glass is then physically manipulated into thin fibres in a way that locates the high RI glass at the core of the fibre. The change in RI as you move from core to cladding is also referred to as ‘optical non-linearity’. Optical non-linearity is deliberately created in optic fibres to improve the efficiency of light transmission.