Nov 20, 2019 in Exploratory

Touch screen technology is considered as one of the most convenient and impressive inventions of the 20th century. It was first invented in 1965 and has since been modified to its present usability on smart phones and tablets as well as laptops among other devices. The touch screen today comes in various types with various capabilities and specifications that give them advantages and disadvantages when compared to others. This means that more often than not, one touch screen is different from the next depending on the manufacturer’s intentions and expected capacity for the product. The Smart phone is among the world’s most popular product especially owing to the brand’s global market penetration. In terms of the technology, the smart phones are seen amongst the most advanced of the phone generation with unique features and capabilities that set them apart from most phones. Their touch screen feature introduced touch screen technology to the mobile phone industry and they have continued to stay ahead in terms of the quality and   intensity of the phone’s touch screen. This paper examines the smart phone’s touch screen. To do this perfectly, the paper analyses the functions and working principles of the touch screen and the required materials and properties necessary for a touch screen. In addition, the paper looks at the materials structure and performance of the screen, environmental impact of the touch screen and availability of new materials that can be used to manufacture touch screens.

Functions and Working Principle of the Touch Screen

A touch screen has been defined as an electronic visual display that can detect and locate the position of the user’s touch within the display area. As such, it can be noted that the major function of the touch screen is to enable the user to interact directly with the contents on the screen instead of using a mouse or a keyboard. The touch screen is thus a direct communication enabler for the device in question, thus making it useful for gadgets like smart phones, game consoles, computers, ATMs and smart TVs among others. 

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There are about four types of touch screen technologies namely resistive, capacitive, surface acoustic wave and optical technologies. Each technology has a unique working principle that is especially relevant to its construction and materials used. The resistive touch screen technology is made up of two layers of conductive materials and the working principle is thus that when the screen is touched the upper layer touches the lower layer thus completing the circuit and causing a voltage change. The screen’s controller is then likely to detect the location of the voltage change thus determining where the screen was touched. 

The capacitive technology on the other hand comprises of a glass panel that has a conductive layer with an equal small amount of voltage applied on all the screen’s corners. When a capacitive screen is touched, there will be some current drawn thus resulting in a voltage drop. The controller is then known to calculate the location of the touch based on the point of voltage drop on the screen. 

The surface acoustic wave touch screens are rather complex in that they rely on waves more than on electric voltage. The surface here has a glass overlay that has both transmitting and receiving transducers. When the transmitting transducers receive electric signals, they convert them into ultrasonic waves before sending them through a reflector to the receiving transducers. Touching the screen absorbs waves and the device can calculate the location using the stored digital map of the screen. 

The optical touch screen technology uses photo detectors and infrared LEDs. When the screen is touched, the infrared LED is interrupted and the reflected LED is detected by the cameras. These cameras then provide the controller with adequate data for calculating the exact coordinates of the touch. This means that in this kind of touch screens, the screen is able to sense the position of the touch using information gathered by interference in the LED.     

All of these touch screen technologies can be used on smart phones as well as on other devices and the choice is usually dependent on the functionality and required specifications of the phone in question. It is often up to the manufacturer to decide on the touch screen technology that would best suit the product at hand. Apple’s iPhone is for example using the capacitive touch screen technology that allows for multi touch functions. The SAW technology is on the other hand more popular with larger devices like tablets and monitors.    

Required Material Properties

If the touch screen uses a resistive or capacitive technology, the required materials for its construction would be polyester, adhesive, glass, and a conductive metallic coating. These are the standard materials that feature in an ordinary touch screen. The required material properties can thus be understood by analyzing these materials and the capacitive touch screen technology, as the most common smart phone touch screen technology will be used to guide this discussion. The idea here is to understand how each part of the touch screen contributes to the functionality of the whole screen. 

Polyester is often for the outer layer of the touch screen and its main requirement is transparency. The polyester on a smart phone’s touch screen is often a hard layer meant to keep the screen safe from a number of contaminants including dust and smudges. Among other things, polyester is known for its resistance to friction and thus high capacity for longevity. They also have a good ability for reflecting light. From this, it can be noted that the required material properties for the touch screen include transparency, strength, ability to endure long and frequent use and a good capacity for reflecting light.  

Adhesives are used to bind materials together and on the touch screen, their role is not any different. The most important factor for the adhesive is its strength and transparency as well as neutrality in that it should not interfere with the working principle of the screen in question. The most common adhesive in this case is the liquid optically clear adhesive that does not interfere with the screen’s optical quality and rather improves its life span. Adhesives must also be able to hold the screen’s parts together in place without showing residual discoloration in the result.    

Glass is the basic part of the touch screen that connects the screen to the LCD part of the phone. This means that among other things, it must be transparent and able to project light to the required level. The glass must also be clear and free from scratches or any interference that may in turn hinder the part from carrying outs its functions. It can be appreciated that this glass panel is the touch screen itself and it is attached to the phone’s LCD display. As such, it must be strong and durable while responsive to the touch. 

Most touch screens also require a controller, which in this case is often the tool used to discern the location of the touch on the screen. A touch controller is often a small chip that is located between the touch screen and the phone and it translates the commands presented on the touch screen to the phone for interpretation and execution. This chip is not necessarily a component of the touch screen from a structural perspective. It is rather a functional associate and is usually located somewhere behind the glass substrate either before or after the phone’s LCD screen.  

The conductive metal coating is found on the inner side of the polyester cover sheet. It can be noted that most of the touch screen technologies involve the passing of electric waves and the metal coating is useful in allowing the touch to be sensed by the device. In most cases, the material used is the Indium Tin Oxide and it coats the both the sides of the glass substrate. It has to be conductive in order to all the effect of touch on the electric voltage to be felt and recorded within the screen. The ITO has to be highly conductive and very durable. Touch screens are already quite expensive as it is and thus one of the basic desired properties of all the constituent parts of the screen is durability.  

Material Structure and Performance

Polyester

This material is basically a polymer whose structure depends on its intended use. In terms of the cover sheet on the touch screen, the molecules have been arranged in two directions creating a mesh kind of pattern. The idea is to provide as much strength and protection as possible without having to be unnecessarily thick. In relation to its performance, it can be appreciated that the polyester cover sheet on a touch screen is expected to be a very thin film that is exposed to touch. This means that the material used in this case must be light enough to allow the touch screen technology to recognize and respond to touch. The mesh concept here is also very useful in ensuring strength and durability of the material. The directional arrangement of molecules in this case acts as a fortification for the material. The fact that it is the outer cover of the screen implies that there is need for environmental endurance and this film must thus be very strong. The fact that it also has to live through a lot of touching means there is need to resist wear. This is how the structure in terms of the arrangement of molecules in this case is relevant to the film’s performance in the touch screen.      

ITO

The ITO layer is made by electron beam evaporation to create ultra thin films that are not only highly conductive but also optically favorable to their role in the touch screen technology. The ability of the film to function within the screen is heavily dependent on its thickness and in this case, the specifications require very minimal thickness with the usual maximum being at 5 mono layers. The film must be able to conduct electricity and ensure transparency such that it does not diminish the optical properties of the screen. The minimized thickness can thus be appreciated as the relevant aspect of its structure that is of great significance to its performance in the touch screen.    

Adhesive

The optically clear adhesive is known for being optically clear and thus useful in the touch screen technology. It is basically an adhesive that is however created for the purpose of the touch screen and display technology like the LCD TV screens. Other than being able to glue the layers together and hold them in position for a long time, this adhesive is also known for its optical qualities. This is the material’s most relevant feature with respect to its role in the touch screen. This adhesive does not only enable the parts to stick together but also enhances the screen’s optical quality by eliminating air in the layers and ensuring that the screen is rather clear. In some cases, screens have been known to have compromised optical characteristics like showing a brighter white and diluting the dark colors. The optically clear adhesive corrects this anomaly by limiting the refraction of light without compromising on the quality of the screen. It has also been known to really help with viewing the screen under the sun. 

Glass Substrate 

This is the glass layer in the touch screen and it is basically expected to be the main part of the screen seeing as it connects the screen to the rest of the phone. This part of the touch screen is usually not more than 0.5 mm thick. The idea is to have as little thickness added on to the touch screen as possible. This implies having to limit the thickness to desirable levels instead of having to create a thick screen or compromising on other parts of the touch screen. This is the substrate layer on which the other layers as mounted. As such, one of its relevant features is its thickness. The glass substrate is the thickest in the touch screen because there is need to keep the rest f the phone safe from damage. This glass rarely breaks and it is well adjusted to harsh environmental conditions.     

Manufacturing Process

Each individual part of the touch screen is manufactured separately to meet the high specifications and to achieve the desired functionality. The polyester film that makes the cover sheet of the screen is manufactured like other polyesters are, except that in this case the molecules are arranged in two directions to create some kind of mesh. The manufacturing process is thus very basic. Once all the parts of the screen have been manufactured, creating the touch screen is not a complicated process. The start of the screen is the glass substrate that is attached to the phone’s LCD display. The ITO is next, followed by the polyester cover sheet. The most important aspect in the process of manufacturing a touch screen is in getting the layers together without trapping air that will end up compromising the screen’s optical characteristics. To ensure that this does not happen, the manufacturers create vacuums between the layers and often use clear liquid adhesives with additional optical abilities like LOCA. Some attention is also often given to the positioning of the electrodes especially in a setting where the touch screen technology in use is capacitive or resistive.      

Environmental Impact

The polyester used in smart phone touch screens is mostly synthetic and in some cases, it is recycled and not necessarily new, as one would expect. This means that they are practically beneficial to the environment as they reduce significantly the number of solid wastes that end up in landfills. Polyester is basically a polymer that can be easily modified to create recyclable plastics as well as fabric among other things. The common components in the metal coating is mostly indium tin oxide, which is basically harmful to the environment if not recycled. The usual options for disposing this compound is the landfills but the periodical incineration would result in serious long term damage to the environment and the health of the populations. This means that manufacturers’ of the smart phones need to be able to collect and recycle their old touch screens to avoid having them in landfills. The glass substrate in this case is mostly not recyclable. The environmental; impact is however minimized by the elimination of alkali from its constituent compounds that usually include a silicon and aluminum component depending on the manufacturer’s specifications. The liquid optically clear adhesive cannot be recycled and the environmental impact is rather minimal owing to its sparing use. 

Possibility of New Materials

The first aspect of the smart phone touch screen that is likely to get outdated first is the ITO. This is because the future of the smart phone is in low processing costs, flexibility, conductivity as well as impressive optical performance. The processing of ITO is a rather complex process that involves vacuum deposition and very high temperatures. This makes it a very expensive material that needs a lot of investment of the part of the manufacturer and eventually the consumer. It is thus very likely that a number of possible contenders like graphene and silver nanowires will replace ITO. Graphene is a sheet of carbon that is only one atom thick and has been going through a lot of study. It has been known to have impressive strength and flexibility as well as the required transparency and conductivity. The silver nanowires are on the other hand a network of percolated silver nanowires that are not just very conductive but also have impeccable flexibility and transparency. This alternative is far cheaper than the ITO despite having superior qualities and abilities in functionality. It thus promises to achieve more popularity as a conducive metal in the place of ITO. 

Generally, the future is inclined towards thinner gadgets with more optical clarity and the ability to be seen clearly even under the bright sunlight. The screens thus need to be lighter and more responsive to the touch, while also cheap enough to be feasible for the manufacturers and the consumers. The idea is to make touch screens that are of such great quality without having to spend a fortune on them. The growing fascination with multi touch will also affect the direction of any new inventions in the touch screen technology since the market in increasingly appreciating devices that are responsive to multiple touches like zooming in and out using the thumb and index finger among other things.       

Conclusion

The touch screen is a great invention that started out as a simple idea for air control and has grown to such impressive dimensions today seeing how large the present smart phone market is. This invention will continue to improve and be celebrated across the world for years to come owing to how easy it makes interacting with one’s devices to be. Depending on the touch screen technology in question, the main materials used include the polyester, glass, ITO and adhesive. Each of these materials have to be strong and yet flexible without really compromising on the optical quality or the responsiveness of the screen. The materials used are mostly recycles to avoid contaminating the environment seeing as most of them are not biodegradable. In the future, there is a great possibility that the ITO will be replaced with more effective and much cheaper alternatives like graphene and silver nanowires. This means that the use of touch screens is mostly like to increase. This means that new gadgets will adopt the use of touch screen technology. Unlike most display technologies, the touch screen technology seems to be the best and there is a high possibility that it will stay for a while.

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