What are the classifications of capacitive touch screens?
The classification of capacitive touch screens is more diverse than resistive screens, mainly based on their working principle, structural integration, and implementation technology
What are the classifications of capacitive touch screens?
The classification of capacitive touch screens is more diverse than resistive screens, mainly based on their working principle, structural integration, and implementation technology. The following is a detailed classification:
I. Classified by working principle and sensor mode (core technology classification)
This is the most essential classification for understanding capacitive screens, which determines their basic characteristics and functions.
1. Surface capacitive type
Principle: Coat a uniform transparent conductive film (such as ITO) on the surface of glass, and lead out four electrodes at the four corners. During operation, a uniform low-voltage electric field is formed on the conductive layer. When a finger touches, it will "suck away" a small current from the contact point, and the electrodes at the four corners calculate the coordinates of the touch point based on the change in current.
Features:
Advantages: The structure is relatively simple, the overall transparency of the screen is high, and it is wear-resistant.
Disadvantages: Can only achieve single touch control; Average accuracy; Vulnerable to environmental interference; Difficult to miniaturize.
Application: Early large-sized public information kiosks, ATM machines, industrial displays, etc. have gradually been replaced by projection capacitors.
2. Projection capacitive type
Principle: Etch a fine, criss crossing (or diamond shaped) ITO electrode array (usually divided into driving electrode TX and sensing electrode RX) on a substrate (glass or film). Accurately locate one or more touch points by scanning and detecting the mutual capacitance of all intersection points (nodes) or the self capacitance changes of each electrode.
Features:
Advantages: Supports true multi touch; High precision and fast response; Strong anti-interference ability; Can be made into complex shapes (such as curved surfaces, irregular borders).
Disadvantages: Complex structure and relatively high cost.
Application: Absolute mainstream technology, widely used in all modern consumer electronics products such as smartphones, tablets, laptops, smart homes, etc.
Two sub technical schools of projected capacitive technology:
Mutual capacitance: detects the coupling capacitance between the intersection of TX and RX. When the finger approaches, it will divert some of the electric field, resulting in a decrease in the mutual capacitance of the node. This is the key to achieving true multi touch, as it can independently detect changes at each intersection without generating "ghost points".
Self capacitance: detects the capacitance between a single electrode and ground. When fingers approach, the electrode's capacitance to ground increases. It is easier to detect and has a high signal-to-noise ratio, but traditional self capacitance scanning can cause coordinate blur ("ghost point" problem) when detecting multiple points. Commonly used for active touch pens and wearable small screen devices. Modern technology can also achieve multi-point recognition through algorithms and special electrode designs.
II. Classification based on the integration of structure and display panel (concepts such as "In Cell")
This is a very important category in modern consumer electronics, especially mobile phones, which relates to the thickness, display effect, and cost of the screen.
external
Structure: The touch screen panel (Sensor+Cover Lens) and display panel (LCD/OLED) are two completely independent components that are bonded together using optical adhesive (OCA).
Type: usually refers to "glass" or "thin film" structures such as GFF/GG.
Features: Mature technology, low cost, high production yield, but thick screen, relatively low light transmittance, and risk of internal reflection.
Applications: Mid to low end mobile phones, industrial control devices, etc.
2. Embedded type
Integrating touch sensors into the interior of a display panel. According to different integration locations, it can be divided into:
On Cell: Embed the touch sensor above the color filter and below the polarizer on the display panel.
Features: Thinner than plug-in type, moderate process difficulty.
Application: It has been widely used in Samsung's AMOLED screens and some mid to high end LCD screens.
In Cell: The touch sensor is directly embedded inside the liquid crystal unit of the display panel or on the TFT substrate.
Features: The thinnest, with the best transparency and the most transparent display effect. But the suppression requirements for display signal interference are extremely high, the process is the most complex, and the cost is the highest.
Application: The mainstream technology of high-end smartphones, such as Apple's iPhone series and flagship models of major brands.
Advantages: Make the device thinner, display clearer, touch more sensitive, and facilitate flexible/foldable design.
III. Classification by Sensor Substrate Material
1. Glass style
Sensors are made on glass substrates (such as GG: cover glass+sensor glass). High hardness, good tactile sensation, and excellent optical performance, but heavy and fragile.
2. Thin film type
The sensor is made on flexible PET film (such as GF: cover glass+sensor film). Lighter, thinner, more impact resistant, and lower cost, but with lower surface hardness (dependent on cover glass) and slightly inferior optical performance.
IV. Classified by special functions and application forms
1. Flexible/Foldable Capacitive Screen
Using flexible substrates (such as PI polyimide) and bendable conductive materials (such as metal grids, nano silver wires) to make sensors, combined with flexible OLED display panels.
Applications: Foldable phones, wearable devices, curved car screens, etc.
2. Anti interference/glove operable capacitive screen
By increasing the scanning frequency, changing the driving signal, and using special algorithms, the signal-to-noise ratio can be enhanced to detect changes in capacitance across gloves or thick media.
Applications: industrial control, vehicle mounted systems, outdoor equipment, etc.
3. Pressure sensing capacitive screen
On the basis of capacitive touch, pressure sensors are integrated (such as utilizing small changes in electrode spacing) to achieve 3D Touch/Force Touch functionality.
Application: Used on devices such as Apple iPhone to achieve quick and easy operation under heavy pressure.
Summary and selection points
Type | Core Features | Main advantages | Typical application scenarios |
Surface capacitive type | Single touch, uniform conductive layer | Simple structure, low cost for large-sized products | Early large-sized public terminals |
Projected Capacitive | Multi touch, electrode matrix | High precision, high sensitivity, multifunctional | Almost all modern touch devices |
External | Separation of touch screen and reality panel | Mature technology, low cost, and easy maintenance | Mid to low end mobile phones, industrial control screens |
Embedded | Integration of sensors and display panels | Ultra thin, good display effect, fast response | High end smartphones |
Flexible capacitive screen | Flexible and Foldable | Freedom of form, impact resistance | Folding phone, curved car screen |
Key findings:
Projection capacitor technology is the absolute dominant technology today.
In Cell/On Cell is a key integrated technology that enhances the appearance and experience of devices.
When choosing a capacitive touch screen, comprehensive considerations should be taken into account: size, whether multi touch is required, thickness requirements (In Cell vs external), cost, environmental adaptability (whether gloves are needed for operation), and special form requirements (flexibility).
