In recent years, the market for biometric sensors in smart phones has grown dramatically. Iris, face and voice recognition are emergent biometric technologies, yet fingerprint sensors currently dominate and will continue to do so. Other biometric techniques are sometimes used, but to complement fingerprint sensors rather than to replace them. Fingerprint sensors have been successful due to their ease of use, fairly low cost, reasonable performance, and a well-developed supply chain.
After a period of very rapid growth, fingerprint sensors were used in an estimated 797 million smart phones in 2016 (only 2.5 million smart phones were shipped with fingerprint sensors in 2012). However, in 2016, fingerprint sensors were included in less than half of all phones sold (just over half if only smart phones are considered), leaving much potential for growth, particularly in low-end smart phones.
From this year onwards, almost all mid-range and high-end smart phones will adopt fingerprint sensors; however, it would be an oversimplification to talk of a saturated market. There is still room to add value in extra features, better performance, and improved ability to image fingerprints successfully under a greater thickness of glass, under metal, under display, and other materials.
In 2017 and 2018, fingerprint sensors will also have growth opportunities in other devices such as notebooks, tablets and smart cards.
A range of different technologies are competing for fingerprint sensor sales, mainly capacitive, optical and ultrasonic. The latter was used for the first time under glass in the Xiaomi Mi 5 shown below.
Capacitive sensors measure the capacitance (essentially the electrical conductivity) between portions of the finger and the fingerprint sensor. Companies using this approach include Apple, Fingerprint Cards, Synaptics, Goodix, IDEX/Cypress, FocalTech, Elan, Egistec and various others.
Capacitive sensors have reasonably strong performance and reliability and a strong market penetration. Leading suppliers now have a strong supply chain, OEM penetration, market experience and production scale, giving them an advantage.
Capacitive sensors generally work well but in more difficult situations such as sweaty or dirty fingers or people with worn fingerprints, sensing can be more challenging and the technology is limited. Overall, false reject rates (FRRs) of around 1–3% are claimed, but higher FRRs can occur in practice with current capacitive sensors in real world situations as illustrated below.
Spoofing capacitive sensors is not difficult given sufficient skill, time and equipment. However, in practice, the level of security is likely sufficient to deter the average thief.
A major disadvantage of capacitive fingerprint technology is an inability to acquire image information through thicker material and/or conductive layers. Capacitive fingerprint sensors can image reasonably well through 250–300 μm of dielectric material, but imaging through thickness above about 400 μm is increasingly difficult. Imaging with capacitive sensors through thicker layers reaches, due to limitations of the underlying physics, a fundamental issue: as thickness increases, the signal spreads out and pixels receive unwanted signals from neighbouring regions, which increases dramatically with thickness and reduces signal integrity.
Implementations with thicker layers is one of the more important reasons why optical and ultrasonic sensors present a serious challenge to capacitive sensors, something which has been recognized by the leading suppliers of capacitive sensors, many of which already have their own research and development on suitable alternatives. The desire to image fingerprints through the conductive features of most display technologies or through metal enclosures such as aluminum or titanium back covers suggests alternate approaches.
Other technologies, such as thermal imaging and use of electroluminescent films, have not made significant progress in consumer devices and do not currently have design wins in smart phones.
Optical sensors can work through thicker glass and plastic layers than capacitive sensors; however, they cannot get 3-D data from below the finger surface. Optical technology has gained recognition from competitors as a viable option, but has not achieved known design wins, and there is a question about the current market readiness of the technology. It is possible that optical technology will win market share in 2017, but this will be significant only if a larger OEM such as Samsung adopts optical fingerprint sensors in at least one model. If it does not, the market share for optical technology in 2017 will likely be 0–2%.
The only company currently focused solely on optical technology is Vkansee, which uses a matrix pinhole imaging system with CMOS image sensors. The Vkansee sensor is described as an “ultra-thin” fingerprint sensor with 2000 pixels-per-inch (PPI) resolution, which is higher than market leaders that use capacitive technology, some of which have a resolution of about 500 PPI. Vkansee believes this leads to better false accept and reject rates (FAR and FRR) as well as good spoof resistance. However, some feel that optical technology in general may be easier to spoof than others such as ultrasound. Optical technology claims high image quality and durability as well as sweat pore detection and recognition. However, studies over the past several decades by organizations such as the FBI and National Institute of Standards suggest that 2000 PPI may be a lot more than needed and that ~500 PPI may be sufficient.
Synaptics entered the market with its December 2016 announcement of an optical sensor, in partnership with Shanghai, China based OXi. Introduction of the Synaptics FS9100 marked the first time that any of the major suppliers of capacitive sensors has expanded its portfolio with a different technology. The new sensor claims under-glass performance up to 1 mm, low-cost integration, a strong IP position, scratch resistance, and water resistance with good wet-finger performance.
However, optical solutions have not yet boasted design wins.
Another exciting technology for the fingerprint sensor market is ultrasound. Ultrasonic fingerprint sensors use ultrasonic waves to map the structure of the fingerprint and potentially the internal structure of the finger. Unlike capacitance (which infers the presence of fingerprint ridges and valleys by measuring the electrical conductivity) or optical technology (which again infers the presence of fingerprint ridges and valleys by measuring the optical index of refraction) ultrasonic technology obtains an image by measuring the difference in density between fingerprint ridges (skin) and fingerprint valleys (air) as shown below.
Companies promoting fingerprint sensors with this approach are Qualcomm, Sonavation and Invensense. However, Qualcomm is the only one with known design wins; that is, it is the only one of the three to have shipped devices in large volume.
A key advantage of ultrasound technology, which it shares with optical technology, is its ability to penetrate through thicker layers of glass and transparent plastic. Unlike optical technologies, ultrasonic sensors can image through metal and opaque glass or plastic layers. This is particularly important as OEMs shift to solutions that are positioned under the display or behind opaque or metal back covers rather than associated with separate, discrete buttons.
Other advantages include higher resolution (in the range of 500–2000 PPI), the potential for scanning the internal structure of a finger (e.g., capillaries) which would make it extremely difficult to spoof, being able to determine heart rate, and an improved ability to cope with sweaty and dirty fingers. These advantages may make ultrasonic technology suitable for high-end consumer or commercial applications (including government and corporate account applications). Ultrasound technology, if it can overcome technical challenges that new technologies inevitably face, has the potential to become the best technology of all for fingerprint sensing.
In 2016, capacitive technology had a 99% market share, ultrasonic technology had less than 1% market share, and other technologies had a negligible share in smart phones.
If ultrasonic sensing can demonstrate reliability and high performance at a cost and power consumption comparable to that of capacitive technology, it should win a strong (but minority) share of unit smartphone shipments in 2017–2020. Optical technology may also win a strong but minority share. Whatever happens, capacitive technology will likely remain the market leader through 2020, with ultrasonic and optical technology taking share only in the high-end market in some designs. However, the capacitive share will decline, and the ultrasonic and/or optical share should increase.
The only known design wins for fingerprint sensors in smartphones not using capacitive technology are Qualcomm’s 2016 wins with Le Eco LeTV Max Pro and the Xiaomi Mi5s. Other suppliers that are focused on non-capacitive sensors (i.e. Sonavation, Invensense and Vkansee) have not yet achieved large-scale, commercial production or design wins.
Qualcomm is now launching an improved, second generation of products at Mobile World Congress in Shanghai. They are a good example of the type of products coming onto the market with disruptive technology and new features.
Qualcomm is offering products that it claims can image through organic light emitting diode (OLED) displays stacks of 1200 μm, 800 μm of cover glass and 650 μm of aluminum. In certain phone designs, this will be a key differentiator against the existing capacitive solutions which have, in some cases, required glass to be etched or a hole to be created to accommodate the sensor. Qualcomm also says it is the only manufacturer of ultrasonic technology that has been able to meet the rigid image quality standards set forth by the FBI and thus obtain FBI certification based on its superior image quality.
In addition to this, Qualcomm’s new products have been designed to work under water and with contaminants such as water, lotion and sunscreen. Heartrate detection is also integrated within the same sensor with liveness being another optional feature. Furthermore, the Qualcomm ultrasonic fingerprint sensors can support gestures; that is, movements such as left/right/up/down, single or double taps, or press-and-hold motions that can be used to activate certain functions more quickly such as taking pictures. Features such as these, assuming they perform as advertised, offer both improved usability for the consumer as well as differentiation for the smartphone OEMs.
Images of the new products are shown below:
The fingerprint sensor market in smart phones has seen explosive growth with many opportunities for further growth and development. Incumbent capacitive sensors compete with emerging ultrasonic and optical technologies. The latter two have a key advantage of being able to pass a good quality signal through a greater depth of material. Therefore, these products have an opportunity to win market share. Of the alternatives to capacitive technology, only Qualcomm is known to have had high-volume design wins. Qualcomm’s latest releases are a good example of how their products and others are evolving to meet the requirements of phone manufacturers and offer increasingly compelling features.