All are off-screen fingerprint recognition technology: what's the difference between the three solutions?

If you want to pick the key words of the smartphone market in 2018, I think the full screen will be able to enter the list of nominees.The whole screen is important, not only because it changes the form of the smartphone, so that the smartphone to obtain a new direction of discovery, towards a higher screen share impact.At the same time, the full screen also makes smart phone biometric technology in two directions.

Some manufacturers, represented by Apple, choose 3D recognition technology and construct face models through structural light for recognition.But such technology inevitably involves bangs.Manufacturers represented by VIVO and others have chosen another route, that is, the off-screen fingerprint solution.Its advantage is to be able to "conceal", avoid bang screen appear.

However, even though it is called off-screen fingerprint recognition, it can be subdivided into optical type, ultrasonic type and capacitive type according to the technical principle and implementation method.The three types of fingerprint identification under the screen are different, and the current development situation is also different.

Optical fingerprint identification under the screen

Optical fingerprint identification is very common in daily life. For example, the punch card used in daily work is the optical fingerprint identification technology, which mainly relies on light reflection to detect the fingerprint loop.Due to the size of the smart phone, the optical fingerprint under the screen can only be used as the light source instead of the original optical system.At the same time, due to the LCD screen can not spontaneous light, so currently support optical screen fingerprint recognition products are using OLED screen.

The technology works by allowing light to pass through the OLED screen's pixels, which are naturally spaced apart.When the user presses the screen with their finger, the OLED screen emits light to illuminate the finger area, and the reflected light that illuminates the fingerprint is returned through the gaps between the pixels of the screen to the sensor that is pressed against the screen below.The final image is identified and judged by comparing with the existing image in the database.

Synaptics' s f9500 fingerprint module

The advantage of the optical off-screen fingerprint sensor is that it can avoid the interference of ambient light to the greatest extent and has better stability in extreme environment.But it also faces the problem of dry finger recognition rate.In addition, since it is to light up specific areas of the screen, it is inevitable that the screen will be prone to aging problems (such as burning screen).Moreover, the power consumption of optical fingerprint is much higher than that of traditional optical fingerprint.

Ultrasonic fingerprint identification under the screen

Ultrasonic off-screen fingerprint recognition technology is based on ultrasonic wave. The ultrasonic wave is firstly transmitted to the finger surface through the sensor and the echo is received.Using the density difference between the skin and air on the surface of the fingerprint to construct a 3D image, and then compared with the information already existed on the terminal, to achieve the purpose of fingerprint recognition.

The advantage of ultrasonic fingerprint identification is that it has strong penetrability and anti-stain ability.The condition of wet and dirty fingers can still be perfectly recognized.In addition, it supports in vivo detection with excellent ultrasonic penetrability.Thanks to the ability to obtain 3D fingerprint identification images, the security is higher than other fingerprint identification schemes under the screen.

However, there are also many urgent problems in ultrasonic fingerprint identification.For example, the imaging quality is low, the technology is not mature enough, the output is low.At present, ultrasonic fingerprint identification under the screen has not been able to get a wide range of commercial applications, because of the above reasons.

Capacitive off - screen fingerprint identification

Capacitive fingerprint recognition technology is no stranger to us. Almost all the commercial fingerprint recognition technologies (excluding the fingerprint under the screen) are based on capacitive fingerprint recognition technology.It is relatively more mature, but it is difficult to transfer capacitive fingerprint recognition to off-screen, and its weak penetration ability is limiting its development.

One solution is to reduce the thickness of the panels that need to be penetrated and avoid the problem of poor penetration by replacing traditional silicon-based fingerprint sensors with transparent glass-based sensors and embedding them directly into LCD panels.When the finger touches the screen, the fingerprint recognition sensor can sense this signal and complete the recognition.

In contrast, capacitive fingerprint recognition does not require the screen to emit light during the identification process, so it supports LCD screen, which is relatively low-cost.However, as there is a layer of touch layer for recognition and touch control on the display screen of smart phones, there may be interference between touch signal and fingerprint recognition signal. This problem remains to be solved.

The development trend of off-screen fingerprint recognition technology

At present, the optical off-screen fingerprint identification technology is more mature, and many suppliers in the industry chain, including huding and Synaptics, have realized mass production of the optical off-screen fingerprint sensor.At present, almost all products equipped with off-screen fingerprint recognition technology, including vivo NEX and huawei Mate RS porsche, adopt optical off-screen fingerprint recognition technology.It can be speculated that in the future for a long time, optical fingerprint identification under the screen will be the absolute mainstream of the market.

At present, the ultrasonic off-screen fingerprint recognition scheme has not been mass produced and is mainly promoted by qualcomm.Back in 2015, qualcomm launched a 3D ultrasonic fingerprint recognition program called Sense ID.In 2017, qualcomm announced a new generation of ultrasonic fingerprint recognition.It is known to be able to penetrate an OLED screen of 1200 m or glass of 800 m and an aluminium alloy of 650 m for fingerprint recognition.

Along with qualcomm, FPC(Finge rprint Cards) of Sweden has its own finger-fingerprinting technology that allows any finger-pointing anywhere on the display, eliminating any physical space constraints on the device's design.Most importantly, it also supports OLED and LCD screens.

However, no matter what kind of ultrasonic fingerprint recognition technology, are facing the problem of mass production commercial.In addition, at the moment when the optical off-screen fingerprint identification occupies the absolute market advantage, even if it finally overcomes the difficulties to achieve mass production, it is really difficult to judge whether smartphone manufacturers will abandon the mature optical off-screen fingerprint identification and turn to the ultrasonic off-screen fingerprint identification.Therefore, it is difficult to be optimistic about the future of ultrasonic fingerprint identification technology.

By contrast, only JDI has launched the capacitive fingerprint recognition scheme.With a technology called Pixel eyes, JDI integrates a capacitive fingerprint sensor with a glass substrate for a TFT display.The glass substrate detects the change of capacitance to identify the finger touch area without the need to add extra fingerprint recognition module.

The advantage of capacitive off-screen fingerprint recognition technology is that it can support LCD screen, thus greatly reducing the cost of the whole machine, which is conducive to the promotion of off-screen fingerprint recognition technology.But as things stand, JDI is still a long way from mass producing the technology.

Conclusion

At present, optical fingerprint recognition technology will be the absolute hegemony of the off-screen fingerprint recognition market for a long time in the future.Ultrasonic off-screen fingerprint identification technology and capacitive off-screen fingerprint identification technology on the one hand, it is necessary to solve the existing technical problems as soon as possible in order to achieve overtaking on curves.The next generation of display technologies, such as microleds, can also be expected.

However, with the continuous progress in the research and development of off-screen camera technology, 3D structured optical system is also expected to achieve off-screen hiding in the future.At present, the advantage of off-screen fingerprint recognition technology is to avoid the appearance of bangs. If 3D structured light technology can achieve "hiding", then it is unknown whether smartphone manufacturers prefer 3D structured light or off-screen fingerprint recognition technology.As for what the future holds for off-screen fingerprinting, time will tell.