There are an isolated few graphics online that look at elements involved in the manufacture of a smartphone – for example, this ‘Periodic Table of iPhones’ – but there’s actually remarkably little easily accessible information out there that details the specific compounds used for specific purposes in mobile phones. This probably isn’t surprising since these details are probably kept under the lock and key of patent laws and the like; however, I tried my best with this graphic to provide a little more detail about specific uses, an undertaking that took a lot more effort than I initially expected!
Details on the elements and compounds involved in the manufacture of touch screens were in fact the easiest to track down. These are manufactured mainly from aluminosilicate glass, a mixture of aluminium oxide and silicon dioxide, which is then placed in a hot bath of molten salt. The purpose of this is to allow smaller sodium ions to leave the glass and larger potassium ions to take their place; these take up more room and are pressed together when the glass cools, producing a layer of compressive stress on the glass and increasing its strength and resistance to mechanical damage.
A thin, transparent, conductive layer of indium tin oxide is deposited on the glass in order to allow it to function as a touch screen – you can read more on how exactly touch screens function here. Several of the rare earth elements are also present in very small quantities, and have a hand in producing the colours displayed on the screen.
The majority of today’s phones use lithium ion batteries. These batteries tend to use lithium cobalt oxide as the positive electrode in the battery (though other transition metals are sometimes used in place of cobalt), whilst the negative electrode is formed from carbon in the form of graphite. It will also have an organic solvent to act as the electrolytic fluid. The lithium in the positive electrode is ionised during charging of the battery, and moves into the layers of the graphite electrode. During discharge, the ions move back to the positive electrode. The battery itself is usually housed in an aluminium casing.
A wide range of elements and compounds are used in the electronics of a phone. The chip, the processor of the phone, is made from pure silicon, which is then exposed to oxygen and heat in order to produce a film of silicon dioxide on its surface. Parts of this silicon dioxide layer are then removed where current will be required to flow. Silicon does not conduct electricity without being ‘doped’ with other elements; this process involves the silicon being bombarded with a variety of different elements, which can include phosphorus, antimony, arsenic, boron, indium or gallium. Different types of semiconductor (P or N) are produced depending on the element used, with boron being the most common type of P-type dopant.
The micro-electrical components and wiring in the phone are composed mainly of copper, gold, and silver. Tantalum is also used, being the main component of micro-capacitors. A range of other elements, including platinum and palladium are also used, but detail on the specific applications of these was a little tricker to track down! Solder is used to join electrical components together – this was, in years past, usually composed of tin and lead, but in recent years lead-free alternatives have been sought, many of which use a combination of tin, silver and copper.
The microphone and speaker of the phone both contain magnets, which are usually neodymium-iron-boron alloys, though dysprosium and praseodymium are often also present in the alloy. These are also found in the vibration unit of the phone.
The elements present in the phone casing will depend on whether the case is metal or plastic, or a mix of the two. Metal casings can be made of magnesium alloys, whilst plastic casings will, of course, be carbon based. The casing will often also contain flame retardant compounds – brominated flame retardants are still often used, but efforts are being made to minimise the use of these, and so other organic compounds that do not contain bromine are now more frequently employed.
There is, I’m sure, a plethora of further information out there which goes into more specific detail about the different chemical compounds used in phones, but this was all I was able to easily track down. If anyone has information that’s more specific, then it’d be great to know!
EDIT: Thanks to @acheronviper on twitter, here’s a little more information on the elements used in semiconductors within a phone:
As noted above, the silicon dioxide layer on the semi-conductor device prevents current from flowing in areas of the semiconductor where this is not desired, namely between the transistors (essentially a form of switches) and the silicon. Transistors are constantly getting smaller and smaller, and as they do so, there is also a requirement for the insulating layer between them and the silicon to become thinner. However, this is limited by the size of silicon atoms, and the fact that, once down to about 5 atoms thick, the layer leaks current and becomes inefficient.
To combat this, hafnium based layers were utilised instead; this also requires use of a different material for the transistors, with both titanium nitride and titanium aluminium nitride being employed. To connect the transistors with the interconnecting copper layers in the semi-conductor, tungsten is used as a contact. Tungsten also finds use outside the semiconductor device, as weights for the vibrating motors within the phone.
Of course, the strive to improve the semiconductor devices still further is ongoing, and the possibility of introducing group III-V element compounds into the transistor structure, such as GaAs, InP and InAs, is a possibility that could allow electron mobility to improve, and in turn allow semiconductors to become smaller still.
References & Further Reading
- ‘What’s in my smartphone?’ – E. Levonas, Mineral Information Institute.
- ‘The Chemistry of Nokia & Sony Mobile Phones’ – A Müller, Geological Survey of Norway.
- ‘Chemical Elements found in Mobile Phones’ – from whatsinmystuff.org.
- ‘Sand to Silicon – The Making of a Chip’ – Intel Corporation.
- ‘Microprocessors – The High-k Solution’ – Institute of Electrical & Electronics Engineers.