5.3 Global warming

Media attention has been such that it would be hard to have missed the fact that global warming is considered to be a ‘bad thing’. Why should this be so? What is so wrong with being a bit warmer? Anyway, is global warming really occurring and, if it is, what are the causal factors responsible for it?

Let us deal with this last question first. As we sit on a beach in summer, or in a sunny window seat in winter, we are aware of the Earth being warmed by the Sun. In fact the Earth is w
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5.1 Pollution and loss of biodiversity

Unfortunately, halting the disappearance of species cannot be achieved simply by measures such as putting fences around special habitats and asking people not to pick the flowers or disturb the breeding birds. Many species are vanishing because of pollution. You probably have a good understanding of the meaning of this term, but it is variously defined. The Open University has a course on environmental control and public health, in which pollution is defined as the introduction into th
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6.2 The hierarchy of human needs

A second approach is to look at the human needs and wants from a more theoretical perspective. One such model was developed in the 1950s and 1960s by Abraham Maslow. Although it exists in many variants it is generally known as Maslow's hierarchy of human needs. In the most common interpretations it places the fundamental material needs of survival, such as food, shelter and safety at the base of a triangle, rising through social needs of belonging in human society, to
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4.4 Discussion

In this second case study, I have described two different trends in energy use by cold appliances over the last few decades. On the one hand the efficiency with which appliances use electrical energy has improved but, in spite of this, their consumption of electricity has increased significantly in recent decades. Since 2000 consumption has started to decline, probably as a result of the introduction of minimum energy standards. The trend will only continue if we demand and use the most energ
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4.1 Distributive and commutative justice

Justice is commonly thought to have two applications which Aristotle distinguished as ‘distributive’ and ‘commutative’ justice. The first, distributive justice, is concerned with the distributions of things (rights, goods, services and so on) among a class of individuals.

What is distributive justice?

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4.6 P is for Provenance

The provenance of a piece of information (i.e. who produced it? where did it come from?) may provide another useful clue to its reliability. It represents the 'credentials' of a piece of information that support its status and perceived value. It is therefore very important to be able to identify the author, sponsoring body or source of your information.

Why is this important?

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4.5 M is for Method

Method is about the way in which a piece of information is produced. This is quite a complex area as different types of information are produced in different ways. These are a few suggestions to look out for:

Opinions – A lot of information is based on the opinion of individuals. They may or not be experts in their field (see P for Provenance) but the key message is to be clear that it is just an opinion and must be valued as such.

Research – You don’t have t
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Introduction

The internet provides a world of information, but how do you find what you are looking for? This unit will help you discover the meaning of information quality and teach you how to evaluate the material you come across in your study of technology. You will learn how to plan your searches effectively and be able to experiment with some of the key resources in this area.

This unit is an adapted extract from the Open University course Author(s): The Open University

5.6.3 Conformation and crystallinity

If there are key connections between the chain configuration and crystallisation, you might also expect some more subtle effects from rotation about chain bonds. After all, polymer chains must be able to twist into the regular conformation demanded for crystal structures (Figure 57(a)). And what influence will rotation have on
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Stage 2: Analysis of the existing situation (where are we now?)

Having defined and agreed on the problem, it is necessary to decide on the system in which you consider it plays a part. In practice the two stages are closely linked and the analysis of the existing system nearly always means a redefinition or refinement of the problem or opportunity. Identifying and defining the problem and the system or systems that relate to it are critical for the success of subsequent analysis.


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2.4.1 Multimode distortion

With multimode fibre, the main cause of pulses spreading is the multiple paths that signals can traverse as they travel along the fibre. This phenomenon of multimode distortion is illustrated in Figure 5.


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6.1 Articulating your appreciation of complexity

I have organized the material in this section so that you can follow the activity route shown in Figure 6.

This section is primarily concerned with what can be understood by the term complexity, and how to compare it with the ideas of difficulty and mess. To do this, you are firs
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8.3.2 Sputter etching: argon ion etching of gold

One commercial process for cutting inkjet printer nozzles uses sandblasting. Not surprisingly, the surface finish is rather poor and there are issues with particles contaminating the devices. However, it is a physical process very like this that we need if we are to achieve a vertical etch profile.

The key is directed bombardment by highly energetic particles. When processing on the microscale, these particles are not sand grains but ions accelerated towards the surface by an electric f
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7.3.1 Electroplating

Electroplating is a relatively fast process, inexpensive and simple, although fairly messy and limited in applicability. The wafer is dipped into a solution with dissolved salts of the metal (e.g. CuSO4 + H2SO4) and is connected to a negative voltage. A positive metal electrode (anode), also in the solution, completes the circuit. Anywhere that current can flow into the wafer surface, metal will be deposited. Plating has several advantages: it will deposit met
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7.3 Depositing metals and alloys

Metal layers are used extensively in device fabrication: to carry current for both power and signals, to apply the voltages that control transistors and generate forces for MEMS, as mirrors and optical coatings, and in magnetic devices for recording media. Different applications might require a continuous film, a long track, multiple thin layers or a plug filling a ‘via hole’ through to a buried layer. The electrical properties resulting from micro structure and composition must be contro
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7.2.5 Stress

Perfect crystal structure can be achieved only by epitaxial growth, where deposits are formed atomic layer by atomic layer. The lattice planes of the deposited film merge seamlessly with those of the substrate on which it is deposited. Even when the crystal lattices of these two materials match in shape, however, they will never be a perfect match in size, owing to differences in atomic spacing between the deposit and the substrate; so, the deposited film will be stretched and distorted to ma
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7.2.4 Microstructure

There are many practical requirements for a film at the microscopic level.

Firstly, it must be firmly bonded to the surface on which it's deposited. A poorly adhered film can peel or flake away under the stresses of later processing steps, or may lead to a reliability issue that will plague the device throughout its lifetime. Similarly, issues can arise with wetting if a deposited material prefers to form droplets on the surface rather than spreading out into a uniform film. A thin adhe
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7.2.3 Chemical composition

As outlined in Table 2, some deposition techniques are best suited to conducting materials, whereas others come into their own only for chemical compounds. In either case, chemical composition may be an important consideration. Impurities can interfere with the conduction properties of the material (notably in t
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7.2.2 Step coverage (conformality)

Not all layers require precise thickness control. Sometimes all that matters is that the film coats the entire surface, including vertical walls and (most difficult) the corners at the bottom of deep holes.

For example:

  • We may require an insulating layer of oxide between two conductors.

  • A protective titanium nitride barrier layer prevents aluminium from diffusing into silicon, and an underlying titanium adhesion layer ensures that
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7.2.1 Thickness control and uniformity

Often, final device characteristics, such as the value of a capacitor, the threshold voltage of a transistor, the resistance per square in a thin-film resistor and the resonant frequency of an acoustic wave filter, depend strongly on the thickness of a deposited layer. Therefore it must be ensured that the layer thickness is the same at all points on the wafer, and on every wafer that comes off the production line. Specifications of ±1% uniformity and reproducibility are not uncommon, and so
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