How Do Touchscreens Work?

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Touchscreens have become a part of our daily lives, from smartphones and tablets to industrial touchscreen equipment and retail systems. The technology dates back to the 1960s when engineers sought more intuitive ways for people to interact with machines.

E.A. Johnson, working at the Royal Radar Establishment in the United Kingdom, developed the first capacitive touchscreen in 1965.

Since then, touchscreens have evolved rapidly. By 2022, the global touchscreen market was valued at $66.91 billion, and it is expected to reach $166.12 billion by 2029, growing at an impressive 13.9% compound annual growth rate (CAGR)

What is Touch Screen Technology?

Touchscreens are an input/output interface that allows users to interact directly with a display by touching it. Touch sensor, controller, and software driver are the three main components of the touchscreen technology stack.

The touch sensor detects the location of touch (from finger or stylus) input on the screen. The controller processes this information and converts it into signals. The software then interprets these signals and executes corresponding actions.

The hardware behind touchscreens is based on different technologies, including capacitive, resistive, infrared, and surface acoustic wave (SAW).

This article will focus on how the two most common types, capacitive and resistive touchscreens, work.

Timeline of Touchscreen Technology Evolution

Before understanding how touchscreens work, let’s briefly look at how touchscreens evolved.

1946 – Philco Company: Direct Light Pen

Philco filed a patent for a stylus used in sports telecasting. It allowed drawing arrows or circles directly onto a live TV broadcast by interacting with a CRT display. Direct light pen marked an early effort to interact with electronic displays.

1962 – AT&T: Optical Touchscreen Patent

AT&T Corporation introduced a touchscreen using a matrix of collimated lights. When a light beam was interrupted, photodetectors identified the touch point. This patent (US 3016421A) marked a significant step in touchscreen technology.

1965 – E.A. Johnson: First Finger-Driven Touchscreen

Eric Johnson, at the Royal Radar Establishment, developed the first capacitive touchscreen which responded to finger touch. His work laid the groundwork for today’s capacitive touchscreens.

Mid-60s – Telefunken: Ultrasonic Curtain for Air Traffic Control

Telefunken created an ultrasonic pointing device which later evolved into a conductively coated glass screen. This technology was patented in 1971 and moved touch screens form a proof of concept to a real world application.

1968 – Frank Beck & Bent Stumpe: Capacitive Screens for CERN

Engineers at CERN, Frank Beck and Bent Stumpe, applied capacitive touch technology to air traffic control. Their innovation led to transparent touch screens used in CERN’s systems during the 1970s.

1972 – University of Illinois: Optical Touchscreen Development

The University of Illinois developed an optical touchscreen with a 16×16 infrared sensor array for the Magnavox Plato IV terminal. This system laid the foundation for future optical touch applications.

1973 – Frank Beck & Bent Stumpe: Early Multi-Touch Technology

Beck and Stumpe (who were working at ) developed a multi-touch capacitive screen capable of detecting multiple touch points. Although it was deliberately limited in functionality, this technology laid the groundwork for future multi-touch designs.

1977 – Elographics: Transparent Resistive Touchscreen

In collaboration with Siemens, Elographics created a transparent resistive touchscreen, first displayed at the 1982 World’s Fair. This became the foundation for many touch interfaces used today.

1982 – University of Toronto: Multi-Touch Camera System

Nimish Mehta developed the first multi-touch system using a camera placed behind frosted glass. This device allowed multi-touch interactions, opening the door to gesture-based technology.

1983 – HP: Optical Touchscreen for HP-150

HP incorporated an optical touchscreen into the HP-150 computer, using infrared transmitters and receivers along the CRT’s bezel to allow accurate touch input. This was one of the first commercial touchscreens.

1984 – Ron Binstead: Projected Capacitive Touchscreen

Ron Binstead patented a “projected capacitance keypad and touchscreen” which could detect touch through thick glass or even air – a leap forward in capacitive touch technology.

2007 – Apple iPhone: Touchscreens for the Masses

Apple revolutionised the touchscreen market with their iPhone. For the first time capacitive touch technology and multi-touch gestures were in the pockets of the averageJoe.

2018 – McDonald’s: Touchscreens in B2B Applications

The fast food giant introduced self-service kiosks with touchscreen interfaces on a large scale, signalling the widespread adoption of touchscreen technology by businesses.

With the history of touchscreens behind us, now let’s look at how touchscreens work.

Resistive Touchscreens

Resistive touchscreens work by detecting pressure applied to the screen surface. Before explaining how the pressure is detected, let’s look at the construction of a typical resistive touchscreen consisting of the following layers.

Top Layer: A flexible, clear polyester film coated with a transparent conductive material, usually indium tin oxide (ITO).
Bottom Layer: A rigid substrate (usually glass) also coated with ITO.
Spacer Layer: Between the two conductive layers, tiny microdots create a small gap that prevents the layers from touching when the screen is not being pressed.
Protective Layer: An outer hard coating to protect the screen from damage.
Conductive Traces: Electrodes arranged along the edges of both layers.

ITO is not the only conductive material used in resistive touchscreens. Metal mesh, silver nanowires, carbon nanotubes, conductive polymers, graphene, and other metal oxides like fluorine-doped tin oxide and aluminium-doped zinc oxide are also used.

When a user touches the screen, the flexible top layer bends and makes contact with the bottom layer at the point of touch.

The conductive coatings on both layers meet, forming an electrical connection. A uniform voltage is applied across one layer (for example, horizontally). When the layers touch, the other layer measures the voltage at that specific point, allowing the system to detect the exact location of the touch.

The touchscreen controller rapidly switches between measuring the X and Y coordinates

For X-coordinate: Voltage is applied horizontally across one layer
For Y-coordinate: Voltage is applied vertically across the other layer

The touchscreen controller processes these voltage measurements to determine the exact location of the touch.

Resistive touchscreens respond to pressure, meaning they can be operated with any object, such as a stylus, glove, or even fingernails.

However, since the technology relies on the physical contact of the layers, it can sometimes result in lower durability over time due to repeated pressure causing wear on the layers.

Pros and Cons of Resistive Touchscreens

Pros	Cons
Durability: Can withstand moisture and stress, making it suitable for industrial and retail environments.	Lower Sensitivity: Requires more pressure to register input, which may be inconvenient for some users.
Versatile Input: Can be used with any object, including fingers (gloved or ungloved), styluses, and other tools.	Poor Display Quality: Offers lower display resolution and can become hazy or yellow over time.
Cost-Effective: Simple manufacturing process with low production cost and power consumption.	No Multi-Touch: Supports only single-touch input, making it unsuitable for applications requiring gestures.
Resistant to Environmental Factors: Functions well despite dust, dirt, and water droplets on the screen.	Prone to Damage: Surface is susceptible to scratches, which can reduce touch accuracy and display clarity.
No Calibration Required: Simple operation without the need for regular calibration.	Lower Light Transmission: Reduces screen brightness and clarity compared to capacitive screens.
EMI Resistance: Good immunity to electromagnetic interference, useful in industrial applications.	Shorter Lifespan: Flexible layers can degrade over time, reducing the overall durability and performance.

Capacitive Touchscreens

Capacitive touchscreens detect changes in electrical fields when a conductive object, like a human finger, touches the screen. Capacitive touchscreens are of two types: surface capacitive and projected capacitive touchscreens.

Let’s look at the construction of a surface capacitive touchscreen.

Protective Cover Layer (Cover Lens): Usually made of chemically strengthened glass (e.g., Corning Gorilla Glass) or hard plastic. It Protects the underlying layers from damage and provides a smooth surface for touch input.
Conductive Layer (Indium Tin Oxide – ITO): Deposited on the underside of the cover lens or on a separate substrate. In projected capacitive screens, this layer is often patterned into a grid of rows and columns. Forms the sensing elements of the touchscreen.
Glass Substrate: A rigid glass layer that provides structural support to the screen and ensures durability. Provides a base for the conductive coating if it’s not applied directly to the cover lens.
Electrode Grid (X and Y Electrodes): Embedded within or between the layers of glass, these electrodes are arranged in rows (X-axis) and columns (Y-axis). They form the grid that creates the electrostatic field across the screen and detect touch events.

Surface capacitive touchscreens work by maintaining a uniform electrostatic field across their conductive layer. A small voltage is applied to the corners of the screen to create this field.

When a conductive object, such as a finger, touches the screen, it distorts the electrostatic field at that specific point.

Electric field changes because human skin is a conductor, allowing it to interact with and change the screen’s electrical properties.

The touch alters the capacitance at the point of contact, and the screen’s controller detects this change. By measuring the change in capacitance, the controller calculates the exact location of the touch. The device then processes the input and performs the corresponding action, such as opening an app or scrolling.

Source capacitive touchscreens can detect one touch at a time. Projective capacitive touchscreens, on the other hand, can detect multiple touches at a time and have different construction and operation.

Projective capacitive touchscreens have a grid of micro-fine wires or transparent electrodes arranged in rows and columns, typically etched onto a glass or film substrate. This grid forms a matrix of capacitors.

The system measures changes in capacitance at each grid node. These touch screens have advanced controllers that can detect multiple touch points simultaneously.

Pros and Cons of Capacitive Touch Screens

Pros	Cons
Durability: Long lifespan with no moving parts, resistant to common issues like dust and moisture, and scratch-resistant surface.	Glove Incompatibility: Standard capacitive screens often do not work with gloves unless specially designed.
Reliability: Maintains performance even if the surface is scratched, as long as the underlying conductive matrix remains intact.	Cost: Generally more expensive compared to resistive touch screens due to the sophisticated technology involved.
Touch Accuracy: High sensitivity, only responds to conductive objects like fingers or specially designed styluses, minimising false touches.	Limited Object Use: Cannot detect touch from non-conductive objects like regular pens or fingernails.
Image Clarity: Made from clear, uncoated glass, providing superior image quality, suitable for high-definition and OLED displays.	Environmental Sensitivity: Affected by the presence of water or other conductive substances on the screen.
Minimal Calibration Required: Requires little to no calibration after manufacturing, unlike resistive screens which need regular calibration.	Higher Power Consumption: Requires more energy compared to resistive touch technology.
Support for Multi-Touch: Can register multiple simultaneous touch points, enabling complex gestures like zooming or rotating.	Proximity Sensitivity: May detect unintended touches when the finger is close to the screen without actually touching it.

Capacitive vs. Resistive Touchscreens

Aspect	Capacitive Touchscreen	Resistive Touchscreen
Working Principle	Detects changes in the electrical field when touched by a finger or stylus.	Measures resistance changes when pressure is applied on the screen.
Multi-Touch Support	Yes, it supports gestures like pinch-to-zoom.	No, primarily supports single touch.
Touch Material	Requires conductive materials (e.g., finger, specialised stylus).	Works with any object (e.g., finger, stylus, gloves).
Sensitivity	High sensitivity, reacts to light touch.	Lower sensitivity requires physical pressure.
Durability	Generally durable with glass surface, resistant to scratches.	Prone to wear and tear due to flexible layers.
Power Consumption	Higher power consumption due to continuous sensing.	Lower power consumption.
Cost	More expensive due to complex manufacturing.	Cost-effective and simpler to manufacture.
Clarity & Image Quality	Superior clarity with no additional layers.	Lower clarity due to multiple layers affecting transparency.
Environment Suitability	Sensitive to moisture and dirt; less effective in harsh environments.	Works well in rugged environments; resistant to dust and water.
Applications	Common in smartphones, tablets, and consumer electronics.	Often used in industrial settings, ATMs, and devices requiring precise input.

Conclusion

Touchscreen technology has come a long way, evolving from simple light-based sensors to the highly responsive capacitive screens we use today. Understanding these differences helps in choosing the right technology for specific needs, whether in industrial settings or consumer electronics. As touchscreens continue to evolve, we can expect even more innovative uses in both business and everyday life.