Core Knowledge of Capacitive Touch Screens
Core Knowledge of Capacitive Touch Screens
Release time：2025-10-24
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Core Knowledge of Capacitive Touch Screens
Capacitive touch screens serve as the interaction core of modern electronic devices. Leveraging advantages such as no physical buttons, fast response, and multi-touch support, they are widely used in various scenarios. Their core information is divided into four parts:
I. Working Principle
Based on "capacitance change detection": The ITO (Indium Tin Oxide) conductive layer inside the screen is made into an electrode matrix through photolithography. When powered on, a uniform electrostatic field is formed; when a human finger (containing electrolytes and acting as a conductor) touches the screen, it forms an "additional capacitance" with local electrodes, disrupting the electric field balance. The driver IC scans the electrodes at a frequency of 100-200 times per second to calculate the position of capacitance changes — self-capacitive screens (e.g., smart watches) achieve positioning through independent detection of X/Y axes, featuring fast response but being prone to "ghost points"; mutual-capacitive screens (e.g., mobile phones) detect changes through electrode coupled capacitance, with a positioning accuracy of ≤2mm and no "ghost points", and a response time of ≤30ms, suitable for high-frequency interaction needs.
II. Hardware Structure (Enhanced Version)
Composed of four core components working precisely in coordination, each layer has more targeted details and processes:
- Surface Protection Layer: Mainstream materials include Corning Gorilla Glass (Mohs hardness ≥6H, resistant to key scratches) or high-aluminum-silicon glass (thickness 0.7-1.1mm, impact-resistant). The surface is coated with an AF (Anti-Fingerprint) coating (contact angle ≥110°, reducing oil adhesion and easy to clean). Outdoor equipment is additionally plated with an AG (Anti-Glare) coating to reduce strong light reflectivity.
- ITO Conductive Layer: The core touch layer with a light transmittance of ≥90% (in the visible light band) and a sheet resistance of ≤15Ω/□ (ensuring stable current transmission). It is etched into diamond/rectangular electrodes through photolithography, with a line width controlled at 5-10μm (about 1/10 the thickness of a human hair) to avoid display impact from overly thick electrodes.
- Substrate Layer: Supports the conductive layer. Mobile phones and similar devices use soda-lime glass (thickness 0.55-0.7mm, flatness error ≤0.1mm/m), while foldable screens use PI (Polyimide) film (thickness 25-50μm, capable of withstanding more than 100,000 folds with a folding radius ≤3mm).
- Driver Circuit Layer: Includes a touch IC (e.g., Synaptics and FocalTech chips, integrated with a 16-bit or higher ADC to filter 50/60Hz power frequency noise), an RC filter circuit (stabilizing current signals), and an FPC (Flexible Printed Circuit) responsible for connecting electrodes and the IC to ensure lossless signal transmission.
III. Purchase Parameters (Supplemented Version)
In addition to basic indicators, key parameters are added, totaling 6 core reference items:
- Touch Accuracy: ≤2mm for consumer-grade (mobile phones/tablets) and ≤5mm for industrial-grade (machine tool panels), tested with a 1.6mm standard stylus.
- Response Time: ≤30ms for consumer-grade (daily sliding) and ≤20ms for gaming devices (avoiding operational delay).
- Light Transmittance: ≥85% after integrating the protection layer (ensuring screen brightness and color reproduction; values below 80% tend to appear dim).
- Operating Temperature: -20℃~60℃ for consumer-grade (indoor/outdoor), -40℃~105℃ for automotive-grade (withstanding high temperatures of the center console), and -40℃~85℃ for industrial-grade (adapting to workshop environments).
- Anti-Interference and Waterproofing: Must comply with the IEC 61000 standard for Electromagnetic Compatibility (EMC) (touch error ≤1mm in the 100MHz-1GHz frequency band). The waterproof rating is IP67 for consumer-grade (1m water depth for 30 minutes) and IP68 for outdoor equipment.
- Touch Lifespan: ≥5 million times for consumer-grade (usable for 137 years with 100 touches per day) and ≥10 million times for industrial-grade (adapting to high-frequency operations of ATMs and machine tools).
IV. Application Scenarios (6 Extended Categories)
- Consumer Electronics: Mobile phones use 6-7.2-inch mutual-capacitive screens (supporting 10-point touch, suitable for pinch-to-zoom), while tablets use 10.9-12.9-inch screens (light transmittance ≥88%, ideal for audio-visual use).
- Smart Wearables: Bracelets/watches use 1.2-2-inch self-capacitive screens (flexible PI substrate, IP68 waterproof support, and wrist-lift wake-up response).
- Industrial Control: Machine tools/robots use 7-21.5-inch industrial-grade screens (resistant to -40℃~85℃, with an anti-oil surface coating and a touch lifespan ≥10 million times).
- Automotive Electronics: Center control screens use 10-15.6-inch mutual-capacitive screens (with an anti-glare coating, complying with the AEC-Q100 automotive standard), and instrument panel touch areas are ≤5 inches (response ≤20ms for switching driving information).
- Public Equipment: ATMs/payment terminals use 15-19-inch surface capacitive screens (30% lower cost, protective glass thickness ≥3mm, and anti-vandalism impact resistance).
- Medical Equipment: Monitors and ultrasound devices use 7-15-inch antibacterial screens (ITO layer doped with silver ions, antibacterial rate ≥99.9%), supporting touch with medical gloves (driving voltage increased to 5V to enhance sensitivity).
In summary, capacitive touch screens achieve interaction by accurately detecting capacitance changes. Understanding their hardware details, purchase parameters, and scenario adaptability enables quick judgment of equipment needs. In the future, they will further upgrade towards flexible and underwater touch technologies.
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