Which touch screen glass is made of overlay?

In the era of interactive technology, touch screens have become an indispensable part of daily life—from smartphones in our pockets to industrial control panels in factories, and from car infotainment systems to retail kiosks. Behind every smooth touch response lies a critical component: the touch screen overlay glass. But what exactly is an overlay in the context of touch screens, and which types of touch screen glass are constructed with this key layer? This article will delve into the details of overlay-based touch screen glass, covering its core functions, technical classifications, material characteristics, and practical applications to help you gain a comprehensive understanding.

What Is a Touch Screen Overlay?

First, it is essential to clarify the definition of a "touch screen overlay." In touch screen technology, an overlay refers to a transparent panel that is placed on top of a standard display (such as LCD, LED, or OLED) to add touch-sensing functionality. It acts as a "smart skin" for the display: the underlying screen is responsible for presenting visual content, while the overlay detects and transmits user touch inputs (such as finger presses or stylus taps) to the controller.

Notably, the overlay is not a single-layer structure. A typical touch screen overlay consists of multiple functional layers, including a top protective layer, a transparent conductive layer, separator components (for specific technologies), and a bottom substrate that adheres to the display. The glass used in the overlay is not ordinary window glass; it is specially engineered to meet strict requirements such as high transparency, scratch resistance, impact resistance, and chemical stability—properties that are crucial for ensuring long-term reliable operation of the touch screen.

Key Types of Touch Screen Glass with Overlay

The overlay design is widely adopted in various touch screen technologies, and the specific structure and characteristics of the glass overlay vary according to technical routes. Below are the main types of touch screen glass constructed with overlays, along with their working principles and advantages.

1. Traditional Protective Cover Glass (Cover Lens) Overlay

The most basic form of overlay glass is the traditional protective cover glass, which is a core component of the "glass-glass (G+G)" touch screen structure. In this design, the overlay exists as an independent protective layer placed above the touch sensor (which is also made of glass). Its primary role is to shield the sensitive internal touch sensors and display panel from physical damage, scratches, dust, and daily wear and tear.

Characteristics: This type of overlay glass is relatively thick (usually 1.1mm or more) and heavy due to the separate protective layer and sensor layer. However, it offers excellent reliability and durability, making it suitable for scenarios with high wear requirements. Common materials include chemically strengthened soda-lime glass (for low-end products) and aluminosilicate glass (for mid-range products). Applications: Early smartphones, basic tablets, and some industrial control devices.

2. OGS (One Glass Solution) Overlay

OGS is a revolutionary innovation in overlay technology that integrates the touch sensor directly onto the inner surface of the protective cover glass, eliminating the need for a separate sensor glass layer. This integration simplifies the touch screen structure and addresses the shortcomings of traditional G+G designs.

Working Principle: The OGS overlay glass is first chemically strengthened, then coated with a transparent conductive material (typically indium tin oxide, ITO). The conductive layer is etched into a grid of microelectrodes to form the touch-sensing structure. Finally, the glass is precision-cut and polished to fit the display size.

Advantages: Compared to traditional overlay glass, OGS reduces the overall thickness of the touch module to as low as 0.7mm, making the device lighter. It also improves optical clarity by reducing light reflection and absorption between multiple layers, resulting in better display effects. Additionally, it lowers material and assembly costs by eliminating one glass sheet.

Challenges: The cutting and etching processes after chemical strengthening can create micro-fractures at the glass edges, reducing edge strength. To address this, manufacturers often use edge polishing and secondary strengthening technologies. Applications: Mid-to-high-end smartphones, tablets, and wearable devices (such as smart watches).

3. TOL (Touch on Lens) Overlay

TOL is often regarded as a subset or upgraded version of OGS technology, focusing on fabricating touch sensors directly on the cover glass with a simpler single-layer structure (without complex bridging circuits). The core difference from OGS lies in the sensor manufacturing process: TOL uses more precise etching technology to ensure sensor stability while maintaining glass strength.

Characteristics: TOL overlay glass inherits the thinness and high transparency of OGS and further optimizes edge durability and touch sensitivity. It supports multi-touch functionality and has better compatibility with curved surfaces (such as 2.5D and 3D glass). Applications: High-end smartphones, curved-screen devices, and car infotainment systems.

4. Resistive Touch Screen Overlay

Resistive touch screens are one of the earliest touch technologies, and their overlay structure consists of two flexible transparent sheets (one of which is glass or hard plastic) coated with ITO, separated by micro-spacer dots. The top sheet acts as the touch-sensitive overlay, and when pressed, it makes contact with the bottom sheet to generate an electrical signal that locates the touch point.

Characteristics: The overlay glass (or plastic) for resistive touch screens is relatively low-cost and can be activated by any object (finger, stylus, gloved hand). However, it has poor optical clarity (light transmittance of 75-85%) and low sensitivity, requiring firm pressure to trigger a touch response. It also does not support multi-touch. Applications: ATMs, POS systems, older GPS devices, and industrial control panels (scenarios with harsh operating environments).

5. Capacitive Touch Screen Overlay

Capacitive touch screens (especially projected capacitive, PCT) are the dominant technology in modern consumer electronics, and their overlay glass is a key component of the touch-sensing system. The overlay glass is coated with an ITO or metal mesh conductive layer, which forms an electrostatic field. When a conductive object (such as a finger) touches the glass, it distorts the electrostatic field, and the controller calculates the touch coordinates based on the current change.

Characteristics: Capacitive overlay glass has high transparency (light transmittance of over 90%), high sensitivity (supports light touch), and multi-touch functionality. It uses chemically strengthened glass (such as Corning Gorilla Glass or Asahi Dragontrail) to achieve excellent scratch and impact resistance. Applications: Smartphones, tablets, laptops, car touch screens, and retail interactive kiosks.

Key Materials and Surface Treatments of Overlay Glass

The performance of touch screen overlay glass largely depends on its material composition and surface treatment technology. Below are the main materials and common surface treatments:

Main Materials

• Soda-lime glass: Low cost, but poor impact resistance. Used in low-end touch devices (such as basic POS machines and entry-level tablets).

  
  

• Aluminosilicate glass: The mainstream material for overlay glass, with excellent impact resistance, scratch resistance, and chemical stability. Used in most mid-to-high-end consumer electronics and industrial devices.

  
  

• Lithium aluminosilicate glass: A high-performance material with ultra-high strength and flexibility. Used in high-end smartphones (such as flagship models) and foldable devices.

  
  

• Glass-ceramic (microcrystalline glass): Features "shatterproof" performance and high hardness. Used in high-end smartphones and rugged industrial devices.

  
  

• UTG (Ultra-Thin Glass): Ultra-thin and flexible, suitable for foldable touch screens (such as foldable smartphones and tablets).

Surface Treatments

• AF (Anti-Fingerprint) Coating: Reduces fingerprint adhesion and makes the glass easy to clean. Widely used in smartphones and tablets.

  
  

• AR (Anti-Reflection) Coating: Reduces light reflection and improves visibility under strong light (such as outdoor use). Applied to car touch screens and outdoor kiosks.

  
  

• AG (Anti-Glare) Coating: Diffuses light to avoid glare and protect eyesight. Used in industrial control panels and large-size touch displays.

  
  

• DLC (Diamond-Like Carbon) Coating: Enhances scratch resistance and reduces friction. Suitable for wearable devices and high-wear scenarios.

Common Applications of Overlay-Based Touch Screen Glass

Overlay glass is widely used in various fields due to its flexibility, durability, and customizability. Here are the main application scenarios:

1. Consumer Electronics: Smartphones, tablets, laptops, smart watches, and portable game consoles. This is the largest application market for overlay glass, with high requirements for thinness, transparency, and touch sensitivity.

   
   

2. Automotive Industry: Car infotainment screens, HUD (Heads-Up Display) systems, and rear-seat entertainment screens. Overlay glass here needs to withstand high temperatures, vibrations, and UV radiation, while ensuring clear visibility and reliable touch response.

   
   

3. Industrial Control: Industrial control panels, machine operation interfaces, and warehouse management terminals. Requirements include high durability, resistance to dust and water, and compatibility with gloved operation (often using resistive or enhanced capacitive overlay glass).

   
   

4. Retail and Public Services: Interactive kiosks, POS systems, ATM machines, and museum exhibition screens. Overlay glass here needs to be wear-resistant, easy to clean, and support multi-user touch interactions.

   
   

5. Healthcare: Medical equipment touch screens (such as ultrasound machines and patient monitors). Requirements include high hygiene (easy to disinfect) and chemical resistance (to withstand disinfectants).

How to Choose the Right Overlay Touch Screen Glass?

When selecting overlay-based touch screen glass, consider the following key factors based on your application scenario:

• Application Environment: For harsh environments (industrial, outdoor), choose glass with high impact resistance and surface protection (such as AG/AR coating); for consumer electronics, prioritize thinness, transparency, and touch sensitivity.

  
  

• Touch Requirements: Multi-touch scenarios (smartphones, tablets) require capacitive overlay glass; single-touch or gloved operation scenarios (industrial control, ATMs) can use resistive or enhanced capacitive glass.

  
  

• Material Selection: High-end products (flagship phones, car screens) choose aluminosilicate or lithium aluminosilicate glass; low-cost products (basic POS) can use soda-lime glass.

  
  

• Surface Treatment: Outdoor or high-glare scenarios need AR coating; daily-use devices need AF coating for fingerprint resistance.

Conclusion

Touch screen overlay glass is the core of interactive touch technology, and its design and material selection directly determine the performance, durability, and user experience of touch devices. From traditional protective cover glass to integrated OGS/TOL solutions, and from resistive to capacitive technologies, overlay-based touch screen glass has evolved to meet the diverse needs of different industries.

Whether you are developing a smartphone, an industrial control panel, or a car touch screen, understanding the characteristics of different overlay glass types and materials is crucial for creating high-quality products. With the continuous advancement of technology (such as the popularization of 3D curved glass and UTG flexible glass), overlay touch screen glass will continue to innovate, bringing more intuitive and smooth interactive experiences to the digital world.

If you need customized overlay touch screen glass solutions for your project, feel free to contact our team of experts for professional advice and support.