Touchscreen displays are able to detect a touch within the active or display area, such as detecting whether a finger is present pressing a fixed-image touchscreen button or detecting the presence and position of a finger on a larger touchscreen display. Some touchscreens can also detect the presence of elements other than a finger, such as a stylus used to generate a digital signature, select objects, or perform other functions on a touchscreen display.
Use of a touchscreen as part of a display allows an electronic device to change a display image, and to present different buttons, images, or other regions that can be selected, manipulated, or actuated by touch. Touchscreens can therefore provide an effective user interface for cell phones, GPS devices, personal digital assistants (PDAs), computers, ATM machines, and other devices.
Touchscreens use various technologies to sense touch from a finger or stylus, such as resistive, capacitive, infrared, and acoustic sensors. Resistive sensors rely on touch to cause two resistive elements overlaying the display to contact one another completing a resistive circuit, while capacitive sensors rely on the capacitance of a finger changing the capacitance detected by an array of elements overlaying the display device. Infrared and acoustic touchscreens similarly rely on a finger or stylus to interrupt infrared or acoustic waves across the screen, indicating the presence and position of a touch.
Capacitive and resistive touchscreens often use transparent conductors such as indium tin oxide (ITO) or transparent conductive polymers such as PEDOT to form an array over the display image, so that the display image can be seen through the conductive elements used to sense touch. The size, shape, and pattern of circuitry have an effect on the accuracy of the touchscreen, as well as on the visibility of the circuitry overlaying the display. Although a single layer of most suitable conductive elements is difficult to see when overlaying a display, multiple layers can be visible to a user, and some materials such as fine line metal elements are not transparent but rely on their small size to avoid being seen by users.
Further, touchscreens are often used to overlay displays such as LCD display screens that have their own circuitry and patterns. It is therefore desirable to consider the configuration of touchscreen electrode patterns when designing a touchscreen.