page_title: Touchscreen
section_title: Capacitive
hierarchical_section_title: Touchscreen / Technologies / Capacitive
caption_attribution_description: English: The Casio TC500 Capacitive touch sensor watch from 1983, with angled light exposing the touch sensor pads and traces etched onto the top watch glass surface.
context_page_description: A touchscreen, or touch screen, is both an input and output device and normally layered on the top of an electronic visual display of an information processing system. The display is often an LCD or OLED display while the system is usually a laptop computer, tablet, or smartphone. A user can give input or control the information processing system through simple or multi-touch gestures by touching the screen with a special stylus or one or more fingers. Some touchscreens use ordinary or specially coated gloves to work while others may only work using a special stylus or pen. The user can use the touchscreen to react to what is displayed and, if the software allows, to control how it is displayed; for example, zooming to increase the text size.
  The touchscreen enables the user to interact directly with what is displayed, rather than using a mouse, touchpad, or other such devices.
  Touchscreens are common in devices such as game consoles, personal computers, electronic voting machines, and point-of-sale systems. They can also be attached to computers or, as terminals, to networks.
context_section_description: A capacitive touchscreen panel consists of an insulator, such as glass, coated with a transparent conductor, such as indium tin oxide (ITO). As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance. Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing. Touchscreens that use silver instead of ITO exist, as ITO causes several environmental problems due to the use of indium. The controller is typically a complementary metal-oxide-semiconductor (CMOS) application-specific integrated circuit (ASIC) chip, which in turn usually sends the signals to a CMOS digital signal processor (DSP) for processing.
  Unlike a resistive touchscreen, some capacitive touchscreens cannot be used to detect a finger through electrically insulating material, such as gloves. This disadvantage especially affects usability in consumer electronics, such as touch tablet PCs and capacitive smartphones in cold weather when people may be wearing gloves. It can be overcome with a special capacitive stylus, or a special-application glove with an embroidered patch of conductive thread allowing electrical contact with the user's fingertip.
  Some capacitive display manufacturers continue to develop thinner and more accurate touchscreens. Those for mobile devices are now being produced with 'in-cell' technology, such as in Samsung's Super AMOLED screens, that eliminates a layer by building the capacitors inside the display itself. This type of touchscreen reduces the visible distance between the user's finger and what the user is touching on the screen, reducing the thickness and weight of the display, which is desirable in smartphones.
  A simple parallel-plate capacitor has two conductors separated by a dielectric layer. Most of the energy in this system is concentrated directly between the plates. Some of the energy spills over into the area outside the plates, and the electric field lines associated with this effect are called fringing fields. Part of the challenge of making a practical capacitive sensor is to design a set of printed circuit traces which direct fringing fields into an active sensing area accessible to a user. A parallel-plate capacitor is not a good choice for such a sensor pattern. Placing a finger near fringing electric fields adds conductive surface area to the capacitive system. The additional charge storage capacity added by the finger is known as finger capacitance, or CF. The capacitance of the sensor without a finger present is known as parasitic capacitance, or CP.
caption: The Casio TC500 Capacitive touch sensor watch from 1983, with angled light exposing the touch sensor pads and traces etched onto the top watch glass surface.
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