What is the principle of fingerprint recognition under the screen? The principle of fingerprint recognition technology under the screen is introduced. Fingerprint recognition technology is now very mature, with a variety of processing methods, as well as technical differences in optical recognition and semiconductor recognition. On the mobile phone side, the most popular attention is the fingerprint recognition under the screen. This identification method is more advanced and the technical requirements are more stringent. Here is a brief introduction to the working principle flow.
Compared with the part of the display area on the screen, the camera and other components are placed for face recognition. The advantage of the fingerprint on the screen is that the integrity of the entire screen can be ensured, and the finger can be directly attached to the screen to recognize and unlock. For users who have already formed muscle memory, the cost of learning is not high.
The core of fingerprint recognition under the screen lies in the sensor, and the first off-screen fingerprint recognition sensor has been released.
SynapTIcs officially released the "World's First Mass Production" off-screen fingerprint sensor - Clear ID FS9500.
According to reports, this sensor is made of optical materials and processes. It can be directly packaged under the AMOLED flexible display or integrated into the OLED screen with a thickness of only 1.5mm. Similarly, it also has the advantage of a screen-based fingerprinting solution – no fear of smudges and mud.
When the FS9500 sensor is activated, the sensor illuminates the fingerprint-recognized area through the upper OLED panel backlight, then transmits the reflected fiber to the underlying sensor and completes the identification process.
Clear ID FS9500 sensor structure schematic
From the launch of the new smartphone market in 2017, almost all major brands have launched comprehensive screen products. According to CINNOResearch's expectations, the penetration rate of full screens in the smartphone market is expected to reach 50% in 2018.
The full screen has become the development trend of smart phones in the future, which is followed by the problem of fingerprint recognition. According to the current state of the art, fingerprint recognition needs to touch the finger, and in order to cater to the market's love for the full screen, the mobile phone manufacturer generally puts the fingerprint recognition system of the smart phone on the back of the mobile phone, or like the iPhoneX. Discard directly, using FaceID.
But in terms of user habits, the experience of fingerprints under the screen is obviously better than facial recognition. All major manufacturers are interested in taking the lead in this field to overcome technical problems and seize market opportunities.
Analysis of the principle of fingerprint recognition technology under the screen The currently known under-screen fingerprint recognition scheme is mainly divided into two directions: one is realized by OLED, and the other is realized by using ultrasonic waves. Let me talk about OLED first. Apple is using OLED screens from Samsung. Although OLED screens have the inherent advantage of shaped cutting, TFT-LCD is not difficult to make shaped cuts, such as Sharp S1 and EssenTIal Phone, both of which use LCD to make shaped cuts, and They are all undertaken by Deput, a subsidiary of Changxin Technology, a listed company in China. Since OLED is not the only choice for a profiled screen, why should Apple choose OLED as the screen for its top-end product? The display effect is on the one hand, the rumored screen fingerprints in the room, it is also likely to be the reason for choosing OLED.
OLED realizes on-screen fingerprint recognition technology
OLED is active illumination. In theory, it can be precisely controlled to each sub-pixel point, so the OLED material screen is a more ideal emission light source. In addition, the OLED display module is thinner and can also reduce the fingerprint sensor tape placed under the screen. The problem of the overall fuselage getting thicker. At present, there are three development directions for the use of OLED screens in the industry chain: 1. A CMOS sensor is placed directly below the screen, and the gap between the sub-pixels of the OLED is used to allow the light to penetrate through the past to identify the fingerprint; 2. The sensor is reduced and the pixel of the OLED is inserted. Between the points; 3, the CMOS sensor is made transparent, directly mounted on the top of the AMOLED screen, and the optical fingerprint recognition is made into a layer of recognition.
In terms of fingerprint recognition under optical screens, many companies have already begun to try and have preliminary results. Huiding Technology has demonstrated the use of AMOLED screens to achieve offline fingerprint recognition. The demonstration models are Samsung Galaxy S7 Edge and vivo Xplay6. Huiding Technology has placed a CMOS sensor at the bottom of the screen. The principle is as shown below.
The location where the fingerprint recognition sensor is placed is illustrated from both a top view and a side view.
From the microscopic point of view, how the light penetrates the OLED screen, the top is the finger; the gray area above the screen is the screen part of the phone. Through the small hole of the screen, the top of the screen is called "Collimator Hole", and the light optical sensor reflected by the finger is collected and processed. Huiding has customized a special microlens array (MicroLens Array) and an optical spatial filter array (SpaTIal Filter Array). The microlens array needs to be processed by MEMS (Micro Electro Mechanical Systems) technology or chemically processed. These two arrays ensure that the light entering the sensor is basically reflected from the fingerprint, not the screen or the sun.
Ultrasound realizes fingerprint recognition technology under the screen
Another screen fingerprint recognition direction is the use of ultrasonic fingerprint recognition. Qualcomm called it Sense ID, and FPC, the leading fingerprinting company, has just released their plan. Ultrasound requires neither photosensitive elements nor capacitive sensing, so it is more suitable for off-screen fingerprint recognition. The full-screen fingerprinting used by the Vivo demo is based on Qualcomm's solution and Oufei's modules.
At present, there are not many ultrasonic fingerprint recognition mobile phones for large-scale applications, mainly LeMus and Xiaomi 5s of Ethyl Ethane. LeMax2 puts the fingerprint on the back, while the millet 5s is on the front side. At that time, the ultrasonic wave can't penetrate the too thick glass, the thickest is about 0.4mm, and the thickness of the mobile phone cover glass is about 0.6mm~0.9mm. The effective thickness of 0.4 mm is not sufficient to penetrate the thickness of the glass + display (0.6 mm + 0.3 mm). Xiaomi had to discuss with Lansi Technology to dig a piece of glass on the front panel to ensure that the ultrasonic energy could penetrate, so the glass in the fingerprint recognition area was thinned. According to information published by Qualcomm's official website, the new generation of Sense ID can penetrate 1.2mm OLED screen or 0.65mm aluminum or 0.8mm glass. This penetration capability is also sufficient for use on current glass or OLED screens.
But why doesn't vivo start to be used on mobile phones such as the X20? This is because a time optimization algorithm is also needed. The new technology needs a debugging process from release to formal application. Fingerprint recognition is a biometric technology with relatively high security requirements. Therefore, it takes time to optimize the algorithm to improve security, recognition speed, recognition rate and so on.
However, the FPC just released the program is even more crazy, FPC said, whether the hand is dry or wet, whether your screen is AMOLED or LCD, even if your surface material is not glass, we can identify. How thick can it penetrate? 20mm! 20mm! 20mm! The important thing is said three times. In contrast, Qualcomm's first generation Sense ID is 0.4mm, and the second generation can also penetrate 1.2mm. FPC can penetrate more than 16 times the thickness of Qualcomm.
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