Overview of touch sensor technology Touch Input: From PCAP to Metal-Mesh with Copper

Related Vendors

VIA Optronics Holding AG

FAULHABER Drive Systems

Touch inputs on displays come in various forms, including PCAP touch, resistive touch, and infrared. Each type offers distinct advantages and disadvantages, making them suitable for different applications. Here's an overview.

*Dr. Jasmin Wagner is Chief Marketing Officer at VIA Optronics.

Touch sensing has long conquered the world of interactive technical applications, not only in consumer electronics, but also in automobile construction and industrial applications. The developments for the different market segments vary to some extent—even if the demand for easy usability and high responsiveness is common to all - and are based on different methods. Here is a brief overview of common touch techniques, their functionalities, and respective advantages and disadvantages.

When a finger or a conductive pen approaches an electrode, it disturbs the electromagnetic field and changes the capacity. The PCAP technique works by detecting the touches—this touch is projected through a glass pane, for example, and changes the capacity.

How different touch techniques work

PCAP Touch is based on measuring the capacity at each addressable electrode. The change in capacitance is measured and converted into an X/Y position, so that the system can assign the touch and recognize the position. PCAP Touch can be used outdoors, is suitable for operation with fingers, stylus, and gloves, supports formats up to 110 inches, temperatures from -40 to 90 degrees Celsius, and is also ready for use at high humidity. Moreover, it scores with high long-term stability and good optical transmittance.

A resistive touch panel consists of two electrically conductive layers, usually ITO (Indium Tin Oxide), on a carrier of plastic/glass and PET (Polyethylene Terephthalate). The two conductive layers are separated by spacer dots. When a finger or stylus touches the surface of the touch panel, the two conductive layers are connected. The upper conductive layer is bent downwards and touches an underlying conductive layer.

The lower conductive layer is energized and then when the two conductive layers are touched, the changes in electrical resistance are determined, which reflects the position of the respective pressure point. The resistance change is transmitted to the system by suitable electronics (controller chip), thus determining the touch point.

This technology can also be used outside of buildings. It can be operated with a stylus or finger. Operation with gloves or multiple touch points (multi-touch) is not possible. Only formats <30 inches are possible. Resistive touch panels are very robust and have a similar temperature and humidity resistance as capacitive touch technology. Resistive touchscreens are more cost-effective than capacitive touchscreens and are still widely used for applications where simple input methods are sufficient.

The Infrared Touchscreen is based on an optical infrared technology, where infrared sensors are built into a frame around the touch area. The built-in sensors have transmitting and receiving functionality, form an invisible light guide grid, which serves for precise detection of the touch point when interrupted.

Infrared touchscreens are not suitable for outdoor use and are limited in temperature and humidity resistance, but find universal use, especially in large interactive display applications. They offer multi-touch function and can also be operated by several users simultaneously. Infrared touch sensors can be retrofitted, allowing use regardless of the display manufacturer.

Better performance with the touch controller

Touch controllers interact with a touch sensor and measure small changes in capacitance or resistance, which are then converted into digital signals. There are many reasons to use a specific touchscreen controller instead of the usual A/D converters in a microcontroller. For instance, implementing capacitive scanning with a general MCU (Micro Controller Unit) can drastically increase the switch-on time and may require more A/D inputs than are available. On the other hand, touch controllers and special touch MCUs can offer higher accuracy, noise suppression, algorithm efficiency, and environmental compensation.

VIA optronics can offer use in conjunction with various touch sensor techniques and apply touch sensor films in curved or flat designs to various substrates. Depending on the requirement, the touch modules can then fulfill different functions, such as single or multi-touch detection, gesture recognition, high environmental requirements for temperature and humidity, the possibility of stylus and glove operation, as well as the deployability of various cover glasses.

Touch sensors based on metal mesh

Due to significantly higher conductivity and flexibility/bendability compared to other sensor technologies such as ITO sensors, the range of applications for Metal-Mesh sensors is very wide in terms of both design and functionality. The manufacturer VIA optronics uses copper-based Metal-Mesh technology in its designs—especially for custom PCAP applications—which has significantly higher conductivity and resistance compared to competing technologies.

The high conductivity allows a quick charging time and thus quick response time of the function, the use of styluses and gloves even with thick cover glasses, as well as excellent multi-touch and gesture function. Since the Metal-Mesh sensors consist of high-resolution metal grids with a resolution of 3 µm, the transparency is significantly better than with other technologies, as only a fraction of the area (transparent film) needs to be covered with Metal-Mesh.

The high-resolution structures also allow minimizing the necessary conductor tracks for connecting the touch sensors, which significantly supports future trends regarding Narrow Bezel and thus larger display area. Compared to ITO sensors and other Metal-Mesh sensors, the flexibility and bendability of Copper-Metal-Mesh is higher or fundamentally given—ITO sensors are not bendable at all, other Metal-Mesh sensors are limited. Therefore, not only flat applications are possible, but also installation in curved surfaces, which gives significantly more design freedom.

The advantages of copper as a sensor element

Copper is used as a conductive material and offers high resistance to temperature, humidity and lifespan, enabling its use in the automotive industry. The copper metal mesh sensors are produced via a roll-to-roll printing and assembly process, ensuring cost-effective manufacturing in large quantities.

In terms of integration, the copper metal grid sensors can be processed by optical lamination, optical bonding as well as by an IML (Inmold Labeling) process. The sensors are always custom-made and allow for high design flexibility. (heh)

This article was first published on our sister portal 'ELEKTRONIK PRAXIS'  (German Edition), Vogel Communications Group