The theoretical basis behind touchscreen technology can be traced back to the 1940’s, but the technology itself was not even remotely possible until the mid-1960’s. The first functioning touch screen device was invented by an electronics engineer known as E.A Johnson in 1965. He was employed by Royal Radar Establishment (known today as the Royal Signals and Radar Establishment), an offshoot of the Ministry of Defence (MOD), based in Malvern, Worcestershire in the UK. He detailed the mechanism that many touch screen devices from smart phones to large format NEC monitors use today. E A Johnson is credited with inventing the first finger governed capacitive touch screen. This technology was primitive by today’s standards. It was binary, meaning that the touch was either picked up, or it wasn’t. In addition, only one touch could be processed at a time. Clearly multi-touch and pressure sensitive technologies were the next step but this was still decades away from full realisation. One of the earliest sectors to make use of this touch screen technology was UK air traffic control, where it remained in use until the very late 1990’s.
What does capacitive mean?
The panel of every capacitive touch screen device is composed of an insulating material, normally glass or plastic. The see through layer is then coated with a very thin layer of a similarly transparent substance which acts as an electrode, which means it conducts electricity. One of the most-common electrodes is a compound alloy called indium tin oxide (ITO), also called tin-doped indium oxide. The substance is, in fact, a 9 to 1 mix of Indium (III) oxide (In2O3) and Tin (IV) oxide (SnO2). In its pure form, it takes on a pale green colour, but when spread as a layer a few molecules thick it becomes ultra-transparent and conductive to electricity. These properties make ITO perfect for touch screen monitors ranging in size from smart phones to interactive retail displays. The human finger acts as an electrical conductor, whereby it conducts electricity away from the screen where it is touched. The computer inside the device interprets the change in the electrical field, and the device carries out the action.
This was the decade in which resistive technology, invented by in the US by Dr. G Samuel Hurst, soon superseded capacitive technology. Whilst working on his Ph.D. thesis at the University of Kentucky in 1970, Samuel Hurst and colleagues used electrically conducting graph paper to read a series of X and Y coordinates simultaneously off a Van-de-Graaf generator. The “eureka” moment happened when the team realised that these points could be read off a computer screen. It was soon discovered that being able to touch a screen directly facilitated interaction and data gathering. The screen needs a conducting cover sheet which allows the current to flow through it and make contact with whatever is touching the screen. Pressing on the surface results in a flow of current which is detected by the device computer and the appropriate action carried out. The big selling point for this resistive technology is that it is cheaper to produce than capacitive technology. It tends to be found in large screen applications such as in manufacturing or the service industries.
In very general terms smartphones tend to employ capacitive technology and larger screen applications such as digital menu boards tend to be resistive. Either way, the discovery and implementation of these technologies is an integral part of the overall development of touch screen technology.