Basic structural analysis of capacitive touch screen

Capacitive touch screens have become the mainstream touch solution for devices such as smartphones, tablets, car infotainment systems, and touch all-in-one machines due to their sensitivity to touch, support for multi-point operations, and long service life. Its seemingly thin and light glass panel is actually composed of multiple layers of precisely stacked functional structures. The core structure can be divided into five parts: protective layer, sensing layer, insulation layer, conductive base layer, and driving control circuit. Each layer works together to achieve the acquisition and transmission of finger touch signals.

1、 Protective layer: the "protective coat" of the touch screen

The protective layer is located on the outer layer of the capacitive screen and is the part that directly contacts the fingers and the outside world. Its core function is to protect the fragile sensing structure inside, while ensuring transparency and touch feel.

The mainstream material is tempered glass, and some low-end devices may use transparent plastic film. Tempered glass has the characteristics of high hardness, scratch resistance, and high light transmittance. After special treatment, it can also achieve functions such as anti fingerprint, anti oil, and anti impact. This layer does not participate in capacitive sensing and only undertakes the tasks of physical protection and visual transparency, serving as a barrier for the touch screen.

2、 Sensing layer: the "perception core" of touch signals

The sensing layer is a key functional layer of capacitive touch screens, which can be divided into two structures: self capacitive and mutual capacitive. Currently, mainstream devices adopt mutual capacitive design, consisting of two layers of transparent conductive electrodes:

Drive electrode (Tx layer): responsible for transmitting drive signals, usually arranged horizontally;

Induction electrode (Rx layer): responsible for receiving induction signals, usually arranged vertically.

Two layers of electrodes are arranged in a grid like cross pattern, and the intersection points form independent inductive capacitor nodes. When the finger approaches the screen, the human body acts as a conductor and forms a coupling capacitance with the electrode, changing the capacitance value of the node. The device can locate the touch position by detecting the capacitance change.

The electrode material is mainly indium tin oxide (ITO), which has high conductivity and transparency, and can accurately sense touch signals without affecting screen display.

3、 Insulation layer: the "isolation bridge" between two layers of electrodes

The insulation layer is sandwiched between the driving electrode and the sensing electrode, and its core function is to physically isolate the two conductive electrodes to avoid direct contact and short circuit, while ensuring the formation of a stable basic capacitance between the two electrodes.

The commonly used materials are transparent optical adhesive, PET film, or insulating materials such as silicon dioxide, which have good insulation properties and do not affect the transmission of light, ensuring that the display effect is not disturbed.

4、 Conductive substrate: the "supporting substrate" of the sensing layer

The electrodes of the induction layer need to be attached to a flat substrate, which is the conductive base layer, mainly made of glass or transparent flexible film.

For rigid capacitive screens, ultra-thin glass is often used as the substrate to ensure a smooth structure and resistance to deformation; For flexible devices such as folding screens and curved screens, the substrate is made of flexible materials such as polyimide (PI) to meet the requirements of bending and folding shapes. The conductive substrate provides stable support for the sensing electrode and is the foundation for maintaining the accuracy of the touch structure.

5、 Drive control circuit: the "processing center" of touch signals

The drive control circuit is located at the edge of the touch screen and consists of touch chips, flexible circuit boards (FPCs), lead electrodes, etc. It is a key part that connects the sensing layer with the device motherboard.

The workflow is as follows: the touch chip continuously sends high-frequency electrical signals to the driving electrode. When the electrode capacitance changes due to finger touch, the sensing electrode transmits weak capacitance signals to the chip. The chip calculates the coordinates, pressure, trajectory and other information of the touch point through algorithms, and then transmits the signals to the device processor to achieve the command response of the screen. At the same time, the circuit also has functions such as anti-interference, multi touch recognition, and false touch filtering.

summary

The structure of a capacitive touch screen may seem simple, but it is actually a precise combination of protective layer, sensing layer, insulation layer, conductive substrate, and driving control circuit. The outer glass provides protection, the middle ITO electrode realizes capacitive sensing, the insulation layer ensures circuit stability, the substrate support structure shape, the control circuit processes signals, and each layer plays its own role and cooperates with each other to achieve smooth and accurate touch experience, making the capacitive screen an indispensable core component of modern intelligent terminals.