Parsing what is 3D touch, what is In-cell

The early phone screens were used only to "see", and the invention of touch technology allowed people to interact with the screen on a 2D plane, while Apple's iphone 6s introduced a combination of the In-cell panel, the strain sensor, and the tactile engine (taptic Engine) opens the new era of smart touch, what exactly is 3D touch technology? What is the In-cell panel?

2D Touch: Let the panel live

LCD panel is only used to display the image, the user can only receive the image information one-way, the appearance of the touch panel, so that users can interact with the panel, so that the panel live up. There are many types of touch panels, and most of the "Multi touch" panels used by mobile phones use "projected capacitive touch (projected capacitive touch)" technology. The touch line of the projected capacitive touch (Sensor pattern) mainly has a drive line (TX) and a Sensing line (RX), respectively, the horizontal and vertical lines are densely distributed throughout the panel, one (a), we can imagine the drive line (TX) "Projection (projected)" Out of the power line, through the insulator (liquid crystal or air) to reach the sensing line (RX) to form a "capacitor (capacitor)", one (b), as shown, because the human body is a conductor, when our fingers touch the touch panel, without force will affect the power line to change the size of the capacitance, A change in capacitance measured by the sensing line (RX) can be used to calculate the position of the finger contact, as shown in one (c).

Figure one: Projected capacitive touch. (a) drive lines and sensing lines on different conductive glass, (b) and (c) drive lines and sensing lines are on the conductive glass below

The drive Line (Tx) of the Touch Line (sensor pattern) and the sensing Line (RX) are there better to do in the end? Each company has its own technology and patents, basically each has advantages and disadvantages, and no decision on the good or bad, simple from the figure One (c) of the LCD panel structure can be seen, can make a touch line of the place is the front of the conductive glass above or below, after the conductive glass three positions above.

In general, the drive Line (TX) is above the rear conductive glass, so that the power line will be projected from the bottom up, and the sensing Line (RX) each company's design location is not the same, Sony and Jdi "Pixel Eyes" to the Rx made on the front of the conductive glass, two (a) shown ; Samsung makes the RX at the bottom of the front conductive glass, as shown in two (b); Apple makes the RX on top of the rear-conductive glass, which is the same place as TX, so the most complex cost of the process is the highest, as shown in two (c).

Figure Two: Drive Line (TX) and Sensing Line (RX) position of the touch line

3D touch: Make panels Smarter

The previously described touch line (Sensor pattern) has a horizontal line and vertical lines are densely distributed throughout the panel, so is a 2D plane touch technology, can only calculate the user's finger contact panel x and Y coordinates position, can not know the pressure of the finger, 3D touch appears, The z-coordinates that allow the user to lower the pressure are also communicated to the phone, making the panel more intelligent.

The "3D Touch", which is used by the IPhone 6s, is not currently publicly available, and according to the film on Apple's official website, there are two important designs:

1. Deformation sensor (strain sensor): Under the LCD panel installed additional 8x12=96 deformation sensor (note), when the user's finger under the pressure to protect the glass, the glass force will be a small deformation downward, three (a) shown, and the protection of the glass and the deformation of the moment between the sensor is shorter, Coupled with the acceleration sensor (Accelerometer) measurement of the signal, through the complex mathematical algorithm can quickly and immediately calculate the strength of the lower pressure, due to the use of indirect estimation algorithm, so the accuracy is not high, basically only divided into "light pressure (Peek)" and "Pressure (Pop)." Any signal detected by a deformation sensor can be compared to the signal detected by other deformation sensors around it, knowing the position and strength of the finger under pressure.

Note: Due to the lack of information disclosed by Apple, this 8x12=96 strain sensor is only vague in the film with "Touch sensor", but according to Apple's patent, there is a high chance of a deformation sensor, please refer to this article for related articles.

2. Tactile engine (taptic): a mechanical element that produces tiny vibrations, as shown in three (b), providing instant tactile feedback from the user, resulting in a 10 millisecond "micro tap" when the user is lightly pressed (Peek), When the user weighs (POPs) 15 milliseconds to produce "Quanzhen (full tap)", the user will feel as if the button is really pressed, the phone's tactile feedback makes the user feel like the phone is alive.

Combined with the above two components, through the deformation sensor to detect the strength of the user under pressure, and then through the tactile engine to provide users with instant tactile feedback, so that the touch becomes more intelligent, but also for the user to create a more perfect touch new experience.

Figure three: Iphone6s's 3D Touch technology combines 8x12=96 with a tactile engine and a deformation sensor

the basic principle and construction of LCD panel

Mobile phones because of small size and battery power, so the display must meet the requirements of light and light power saving, is mainly used "liquid crystal display (Liquid crystal DISPLAY,LCD)". The structure of the LCD is shown in four, the path from the bottom down along the light is followed by a backlight module (back), a rear polarizer (polarizer), a post-conductive glass, a thin-film transistor (Thin Film transistor,tft), a liquid crystal (Liquid crystal). , Colour filter (color filter), front conductive glass, front polarizing film (Analyzer), protective glass (Cover glass), etc., the structure and principle are somewhat complex, here we do not introduce in detail (for the LCD working principle is interested please refer here).

Mobile phone due to small size and power-saving, so the use of light-emitting diode (light emitting diode,led) as a source, conductive glass is a thin layer of glass substrate "indium tin oxide (indium tin Oxide,ito)" to form a conductive glass, Ito is a kind of ceramic (metal oxide), almost all of the ceramic is an insulator, but the ITO can not only conductive, but also transparent when the thickness is very thin, can let the visible light penetrate, so a large number of applications in various optoelectronic components.

In addition, the semiconductor process technology must be used above the post-conductive glass to grow "switch element", the simplest switching element is "MOS", but MoS has a metal, oxide, semiconductor structure, must grow on the silicon wafer, to grow on the conductive glass on the switch element can not use MOS, A switch element must be designed in addition, and it works like a MOS, which we call "thin film transistors (Thin Film transistor,tft)" (see here for the structure and principle of MOS).

On the rear conductive glass has a TFT switch element panel called "Active Matrix", the switch is near the pixel so the reaction is faster; a panel without a TFT switch element is called a "passive matrix (Passive matrix)" The switch element of this panel is made on the printed circuit board (PCB) outside the panel, the switching distance pixels is far away, so the reaction is relatively slow, guess what is AMOLED? The organic light Emitting bipolar body (Organic-emitting diode,oled) also has a post-conductive glass, so AMOLED is a TFT switch element on the post-conductive glass.

Figure Four: The basic principle and construction of LCD panel

What is a cell? What is Out-cell, On-cell, In-cell?

LCD production process is first in the "front conductive glass" under the Ito side of the production of switch lines and color filters, on the "post-conductive glass" on the Ito side of the production of switch lines and TFT, and then the front and back of the two-piece conductive glass of the Ito side clip up, and the liquid liquid crystal injected into two conductive glass, form the structure of Figure Four (b), this process is known as "Panel Engineering (Cell engineering)", so the area between the two conductive glass is called "Panel (Cell)", in fact, the steps of panel engineering is quite complex, interested people can refer to this site.

The touch panel requires "touch Line (Sensor pattern)" To determine where the user's finger is selected, and if the touch line is first made on a protective glass (Cover glass) and then adhered to the front conductive glass (i.e. outside the cell) on the Panel (cell), it is called " Out-cell ", as shown in five (a).

Figure V: The location of the touch line (omit the color filter in the picture).

If the touch line is directly above the front conductive glass (i.e., on the cell) of the Panel (cell), it is called "On-cell", as shown in five (b); If the touch line is made directly between the front and back conductive glass (i.e. inside the cell) of the Panel (cell), it is called " In-cell ", as shown in five (c). From the figure can be seen In-cell the biggest advantage is the thickness of thin, so now has become the mainstream of smart phone panels, but there are high prices and touch lines susceptible to the interference of the TFT and switch lines, so Out-cell and On-cell still have the value of existence, Can be applied in other large size or thickness requirements of the product.

Parsing what is 3D touch, what is In-cell