Smartphones, in general, may appear to be plateauing, but that is an over-generalization that takes away from the exciting development that does happen. For instance, in the past few years, we have seen capacitive fingerprint scanners slowly be replaced by in-display fingerprint scanners, mostly of the optical kind but some ultrasonic too. These in-display sensors first made their appearance on flagships, but the technology has slowly made its way lower down the market too. However, one drawback of these current generation in-display fingerprint sensors is that they work only with AMOLED displays, which adds on to the overall cost of the product. Now, Redmi has showcased in-display fingerprint sensor solutions for LCDs, and it claims this tech is mass production-ready.

Redmi General Manager, Mr. Lu Weibing took to his Weibo account to share a short clip demonstrating the in-display fingerprint scanner technology for LCDs.

According to Mr. Weibing, Redmi, the Xiaomi-backed sub-brand, has managed to successfully incorporate infrared-based in-display fingerprint scanner tech for LCD. He goes on to give a short summary, explaining that the working principle behind in-display fingerprint scanners is to record the characteristics of the fingerprint through the sensor that sits underneath the display. Since the sensor is under the display, there needs to be a channel to transmit either optical or ultrasonic signals, which limits the current generation solutions to OLED displays only as LCDs have a backlight module that does not allow this to happen. By extension, these in-display fingerprint scanners are thus limited to higher-priced devices since OLEDs are more expensive than LCDs. LCDs can only use back fingerprint scanners or side-mounted fingerprint solutions as seen on the POCO X2 (or Redmi K30, as it is known in China).

The Redmi R&D ream has overcome the technical limitations by using infrared high-transmittance film material. This film greatly improves the transmittance of infrared light through the display, which could not happen previously. This is different from optical fingerprint scanners which basically captured a photo of your fingerprint through a camera, as this makes use of infrared transmitters below the display to capture the fingerprint.

Redmi says that this approach successfully overcomes the hurdles of in-display fingerprint on LCDs. Though it remains to be seen how secure this approach actually is, and if it is better than optical in-display solutions, could this be adapted to OLED displays as well? Another element is cost, as LCDs are primarily adopted for their lower cost -- if the IR solutions is more expensive, it would defeat the cost benefits that come from using LCD.

LCDs with in-display fingerprint scanners were expected to bring the tech down to lower price points. Goodix was also confident of LCD optical under-display fingerprint scanners entering mass production in 2020. It remains to be seen how Redmi's IR based solution affects these plans, as Redmi has not given a timeline for a consumer product either.

Source: Weibo