Influence of Touch Sensor on Capacitive Touch Screen Performance
summary
The performance indicators of capacitive touch screen can be divided into: signal-to-noise ratio, anti-RF interference ability, scanning speed, waterproof, operating temperature range, anti-aging, power consumption, ESD and packaging, etc. Signal-to-noise ratio is the core indicator. Most of the performance in the user experience depends on the signal-to-noise ratio.
For example, the accuracy of the touch coordinates, the size of the jitter of the touch coordinates, and the linearity of the scribing line all depend on the signal-to-noise ratio. Devices using capacitive touch screens have different working environments, and the suitable temperature range must be wide, otherwise it may cause changes to users. Typically capacitive touch screens
The operating temperature range is -20°C~70°C. These requirements are related to two important components in the capacitive touch screen: touch IC and Touch sensor. Touch IC can be easily selected, but Touch sensor is not the same, each manufacturer’s products are different.
Capacitive touch screen is the most widely used touch screen. For capacitive touch screen, the two most important components are touch IC and touch sensor. Touch IC can be selected according to the manufacturer’s specification, but touch sensor is a completely customized product.
1.The impact of Touch Sensor on the performance of capacitive touch screen.
2.What is the ITO circuit of the Touch sensor?
The impact of Touch Sensor on the performance of capacitive touch screen.
The touch sensor is the sensor, and the touch IC is the analog-to-digital converter. The touch IC controls the electrical signal to scan continuously on the circuit of the touch sensor to detect the change of capacitance, so the process and material of the touch sensor directly affect the quality of the signal received by the touch IC.
The TX and RX of DITO are made on both sides of the substrate, and the substrate is used as an insulating layer (usually a glass substrate). The TX and RX of SITO are all on one layer without insulation layer. So, the performance of double-sided ITO will be better. At present, there are two mainstream capacitive touch screen structures: 1. G+G structure: glass substrate double-sided ITO touch sensor and glass cover plate, 2. G+F+F structure: film substrate single-sided ITO touch sensor + film substrate Single-sided ITO touch sensor + glass cover.
From the perspective of substrate materials, sensors are mainly divided into two categories, namely Glass substrates and Film substrates. Glass substrates can realize single-sided ITO sensor and double-sided ITO sensor, and film substrates only support single-sided ITO process.
Single layer ITO pattern glass structure
Double layer ITO pattern glass structure
Double layer ITO pattern film structure
What is the ITO circuit of the Touch sensor?
The ITO circuit of the Touch sensor is made of ITO (indium tin oxide). There are generally two processes: the first is to transfer the ITO to the substrate by magnetron sputtering and then etch away the excess part. Due to the high temperature during the production process, only use glass substrate. The other is the circuit formed by printing. The low temperature of this process can use high-temperature-resistant transparent films such as polyimide as the substrate to achieve a lighter and thinner structure. Both processes are now widely used technologies, the touch sensor of the Glass substrate and the What are the advantages and disadvantages of the touch sensor of the film substrate?
| project | glass substrate | film substrate |
| process | Using magnetron sputtering and etching processes or printing | just printing |
| material dielectric constant | 4-7 | 2-3 |
| Transmittance | ≥85% light transmittance is good | ≥80% |
| lifetime | long life, not easy to damage | Easy to yellow, shorter lifespan than glass ITO sensor |
| sensor line width and spacing | Narrowest 30um/30um, usually 50um/50um | Narrowest 100um/100um, usually 120um/120um |
| thickness | sensor ITO layer thickness is 0.7um | sensor ITO layer thickness is 0.4um |
| Lamination layers of capacitive touch screen | 2 layers | at least 3 layers |
| ITO square resistance | 75ohm-100ohm | 150ohm-300ohm |
| sensor cutting process | Sensor is more difficult to cut special-shaped | easy to cut |
| Lamination yield | Simple process, high bonding yield | Many layers, low bonding yield |
| making molds and product unit prices | The cost of mold opening is high, but the unit price is low | The cost of mold opening is low, but the unit price is high |
What are the touch patterns?
In order to achieve a better touch effect, the lines of the touch sensor are arranged on the base material, and they are designed into different types. This is called the pattern of the touch circuit.
hexagonal mesh pattern
Diamond Mesh Pattern
polygon mesh pattern
rectangular mesh pattern
conclusion
If you have requirements on the performance of the touch screen, it is recommended that you choose a touch screen with a structure of G+G (Cover Glass+ITO touch sensor of glass substrate) or G+F+F (ITO touch sensor of cover glass+two-layer film substrate) structure, which can for better performance.
When choosing capacitive touch screen, it is also necessary to pay attention to the ITO touch sensor of the glass substrate, which is usually used on a larger tft display, and the thickness is relatively thick in order to maintain strength. ITO touch sensors with thin film substrates have no limitation in size but have poor light transmittance and durability.
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