【TrendForce View】Will Snapdragon 855 Spell Doom for Capacitive Fingerprint Sensors?

(Source : Qualcomm)

Qualcomm has just officially unveiled Snapdragon 855, its next-generation mobile SoC for flagship smartphones. Among the highlighted features of this new platform, the support for under-display ultrasonic fingerprint scanner is getting just as much excitement as its 5G capability. This also points to a major trend in the context of smartphone design — the all-screen front. Currently, there is a strong push in the market to elevate the all-screen design as the standard in the flagship segment. As smartphone makers trim down the width of the bezel and extend the screen to the edges of the device, the conventional fingerprint sensor module will have to be replaced by other types of biometric sensor technologies that do not compete with the display for surface area. This is also the reason why the under-display fingerprint scanner is gradually becoming an essential feature in smartphones. By supporting and promoting ultrasonic fingerprint scanners, Qualcomm intends to rise above its competitors in the biometric sensor market.

The trend of all-screen design began with the releases of Samsung’s Galaxy Note 8 and Apple’s iPhone X in the second half of 2017. In order to allow the display to practically occupy the entire face of the device, branded smartphone makers have to make some changes and compromises. For Note 8, Samsung moved the fingerprint scanner to the underside of the device and placed it next to the rear camera. In the case of iPhone X, Apple replaced the familiar home button with a novel facial recognition technology. At that time, the under-display fingerprint scanners were not a viable option because they had yet to reach technological maturity.

The development of under-display fingerprint scanners has been a slow and difficult journey

How to integrate the fingerprint scanning module underneath the smartphone display panel has been a longstanding challenge for companies developing solutions for fingerprint recognition. Among the various biometric sensor technologies, the capacitive sensors are the most mature for fingerprint recognition because they have better signal-to-noise ratios that translate to higher sensitivity. For a capacitive fingerprint scanner to work effectively, the tip of the finger and the sensor have to be very close to each other, within the optimal distance range of 350 micrometers to 0.35 millimeters. However, most types of cover glass protecting the smartphone display have thicknesses ranging from 0.8 to 1 millimeters. Since signals from the capacitive sensor cannot go through the cover glass, smartphone makers have to embed the sensor module in a hole that they cut in the glass. The sensor module can also be integrated with the home button, and they together will become a separate interface that is below the screen area of the device. Recently, smartphone makers have also embedded the capacitive fingerprint scanner on the backside of their devices in order to increase the screen-to-body ratio.

The relatively new optical and ultrasonic sensors represent an important breakthrough because they can be integrated underneath the smartphone display. The US-based Synaptics pioneered the development of under-display optical fingerprint scanners. The costs of its solutions in 2017 were in the range of US$12 to US$15. However, prices are falling due to the rising number of competitors such as Goodix and Silead and Egis. The average cost of the optical solutions is projected to drop under US$8 in 2019.

Qualcomm focuses on under-display ultrasonic fingerprint scanners

Qualcomm is leading the charge in the development of under-display ultrasonic fingerprint scanners. The company actually has been working on the technology for several years. In 2013, Qualcomm acquired Ultra-Scan, which was one of the first to apply the ultrasound technology to fingerprint recognition. Later in 2015, Qualcomm unveiled its ultrasonic solution called Sense ID. Since then, Sense ID has been incorporated as part of the Snapdragon platform.

Downscaling was a bottleneck in the development of ultrasonic fingerprint recognition solutions. An ultrasonic fingerprint scanner contains a piezoelectric sensor that detects pressure exerted by the finger. Previously, a piezoelectric sensor would have to be supported by a special capacitor that can hold a driving voltage of at least 100 volts. The entire setup, however, cannot fit into smartphones or other mobile devices. To solve the size problem, Qualcomm developed a patented fabrication process that applies a form of MEMS-CMOS integration onto the array of piezoelectric micromachined ultrasonic transducers. Hence, the new generation of piezoelectric sensors for the under-display ultrasonic fingerprint scanners are now small enough to fit into the mobile SoC. Their driving voltage has also been reduced to just 24 volts.

The piezoelectric effect that is the principle behind the operation of an ultrasonic fingerprint scanner refers to the electric charges that are produced within certain materials (i.e. special ceramics) when mechanical stress is applied to them. As piezoelectric materials are under pressure, their electric dipole moment decreases, thereby creating charges of different polarities. These charges in turn can be converted into digital signals.

When a finger is pressed on an ultrasonic fingerprint scanner, the ultrasonic waves emitted by the scanner will be able to detect the spatial distribution of the pressure across the sensing area. The pressure is unevenly applied because of the ridges and valleys in the fingerprint, so there will be a unique and identifiable pattern that can be captured by the piezoelectric sensor. Furthermore, the ultrasonic waves can penetrate the outer layer of the skin. They therefore can map the locations of sweat pores on the finger and even determine the skin pigmentation. This is in addition to the topological features of the fingerprint that the scanner can process. Hence, the ultrasonic fingerprint scanner is also an advanced 3D fingerprint recognition technology. Its accuracy is generally unaffected by the contaminants on the surface of the finger (e.g. oil, lotion, sweat, and condensation) and by the materials that protect the smartphone (e.g. glass, sapphire, and metals).

Will there be changes in the market for fingerprint recognition solutions?

TrendForce forecasts that Qualcomm’s products will account for 4.4% of the global market for fingerprint recognition solutions used in smartphones in 2019. Samsung is reported to plan on using Qualcomm’s ultrasonic solutions for its under-display fingerprint scanning feature in 2019. This implies that the domination of the optical solutions as the only viable technology in the market for under-display fingerprint scanners is coming to an end. TrendForce also forecasts that the global market for under-display fingerprint scanners will grow by several folds in terms of scale in 2019.

Although Qualcomm is a late entrant in the market for fingerprint recognition solutions, it may pose a strong challenge to the established players in the future. If Qualcomm does succeed in getting Samsung to adopt its ultrasonic solutions for the brand’s flagships, it will then have a better position in introducing its technology to the flagships of Chinese brands. Qualcomm’s success will also affect competitors’ strategies, especially their approaches to the mid-range and high-end segments of the smartphone market. Those that are working with both capacitive and optical sensing technologies, including Goodix and Silead, may have to significantly lower their prices in order to remain on the supply chains of major smartphone brands. On the whole, the introduction of the new technology and the price competition are expected to erode the market shares of suppliers of the mainstream fingerprint recognition technologies in the future.

Apart from the the back-and-forth competition among smartphone brands, the struggle among suppliers in the market for fingerprint recognition solutions is also a major highlight worth paying attention to.

Fingerprint Recognition Technologies for Smartphones — Their Global Market Shares and Suppliers(Source: Topology a division of TrendForce)