Qualcomm says the second generation ultrasonic fingerprint sensor with larger area of recognition will arrive during the second half of this year. During a closed door briefing held on the sidelines of Mobile World Congress 2019 in Barcelona, Gordon Thomas, Director, Product Management on Qualcomm 3D Sonic Sensor, confirmed that the company is preparing to commercialize ultrasonic sensor with area of recognition bigger than first generation model in the second half. The San Diego-based chipmaker showcased the ultrasonic fingerprint sensor for the first time in 2017 at Mobile World Congress in Shanghai but the technology is debuting on a commercial product only this year.
Samsung Galaxy S10, Galaxy S10+ and Galaxy S10 5G announced at Unpacked event last month are the first and only devices to feature Qualcomm’s 3D Ultrasonic fingerprint sensor. The sensor embedded under the display has an area of 36 square millimetre and has a dimension of 4 x 9 mm. The second generation of Qualcomm’s ultrasonic sensor will have a dimension of 8 x 8 mm and thus offer a large area of recognition equivalent to 64 square millimetre. Interestingly, the thickness of the sensor will remain the same at around 200 micron despite the increase in area.
The under display fingerprint sensor is not new in the smartphone world and smartphone makers like OnePlus, Oppo and Vivo have already used optical sensors on their devices. Qualcomm, however, has devised a new solution altogether, which it calls as ultrasonic sensor. It consists of three main elements – an ASIC that drives the sensor, a FPC connector and the sensor. Thomas explains that the main layer of the sensor is the glass layer, which is used as substrate on which the circuitry resides. The 3D sonic sensor from Qualcomm does not use silicon, which makes it both cheaper and easier to scale. Qualcomm says the sensor with the glass layer alone is not much different from the capacitive sensor but once it is coated with other layers such as piezoelectric layer and RX and DX electrodes, the ultrasonic sensor takes its own shape.
How ultrasonic sensors work
While the ultrasonic sensor sounds similar to that of optical sensor, it is fundamentally different when it comes to form and function. In the case of an ultrasonic sensor, whenever users touch the display, there is an electrical signal sent from the ASIC to the sensor. This electrical signal is then converted into a pressure wave which goes onto hit the finger and gets reflected back.
According to Thomas, the pressure wave is reflected back with different densities depending on whether it touches the skin or air gap in your finger. No matter whether your finger is wet, dry or completely submerged under water, there is different density allowing the sensor us to capture black or white on your fingerprint. “One of the advantage of a 3D Sonic Sensor is that we don’t use light from the display so you don’t see that bright light shining on the Galaxy S10 display,” Thomas said.
Qualcomm team behind the 3D Sonic Sensor explain that the new ultrasonic sensor is around 200 microns thick while the optical sensor with its camera module is around 3mm in total thickness. The ultrasonic sensor comes with multiple advantages that can be broken down into areas such as Security, Battery, User Experience and Quality of Display.
Smartphone makers using under-display optical fingerprint sensors do not advertise them as secure. Qualcomm and Samsung, on the other hand, are pitching the ultrasonic sensor as one that offers vault-like security and is anti-spoof.
Challenges to under-display authentication
Thomas explains that if you use your phone for over a year and a half, there is something called image blurs formed on the display and the optical sensors have those issues and the OLED itself gets damaged in that area. He adds that if you are constantly touching the display then one can see oily residue left on the screen.
The residue can be exploited to unlock the device by taking a glossy white paper and sticking it on there. This will unlock the optical sensor since the optical light will reflect from the oily fingerprint and reflect from the glossy paper to create a nice contrast ratio, emulating itself as a fingerprint to the optical sensor.
“In the case of ultrasonic sensor, the sound will travel through all of these patterns and will not reflect back allowing for 2D anti-spoofing,” adds Thomas. He says Qualcomm has also added a machine learning algorithm called anti-spoofing bioimpedance that prevents spoofing using certain materials which are similar to skin. There are materials which can be used to build a fake finger using those materials and it is possible to unlock a phone with an optical sensor.
However, the same trick cannot be applied on ultrasonic sensor prevented by anti-spoofing bioimpedance. The new ultrasonic sensor developed by Qualcomm is so advanced that it is the first sensor to be certified by FIDO Alliance, which certifies sensors for their security.
Since the ultrasonic sensor does not rely on light from the OLED panel, it is also not affected by direct sunlight. Qualcomm says its ultrasonic sensor cannot be spoofed to access with photograph of your fingerprint. Since the sensor is based on TFT substrate material and does not involve any silicon, it gives ample opportunity for scaling the technology.
While the sensor used on the Galaxy S10 series is 4×9, the next sensor will be of 8×8 in dimension and the company is also working on a larger 30×20 sensor with an area of 600 square millimetre. The devices with 8×8 sensors are expected to arrive in the second half while the 30×20 sensor will be commercialized in the second half as well. Qualcomm says it intends to scale the ultrasonic sensor without increasing the thickness of the sensor.
Watch: Samsung Galaxy S10 Series First Look
The launch of Galaxy S10 and Galaxy S10+ with ultrasonic sensor is just the start. Qualcomm says it plans to add additional features such as blood flow, heart rate monitoring that doesn’t exist right now with future generation. It also plans to enable the sensor to wake up the phone in the future. Right now with all under display sensors, the touch screen wakes up the phone or the power button or the gyro is used to wake up the phone. “With this feature, the fingerprint sensor will itself be capable of waking up your phone. This will eliminate touchscreen out of the equation, translating into saving of 200mA of power at standby,” Thomas said.
The immediate plan for Qualcomm is to allow for multi-finger authentication with the introduction of a larger area sensor. Qualcomm is also working on a sensor that will cover the entire display where it aims to turn the sensor to act as touch screen or stylus layer. “We can combine touch, stylus and fingerprint into one layer without adding more volume,” Thomas said. While this sensor will first debut on smartphones, Qualcomm also sees them being used on automobile and other use cases.