Vivo X20 Plus UD: First In-Display Fingerprint Sensor

The Vivo X20 Plus UD was the first smartphone with an in-display fingerprint sensor, launched in January 2018. It used a Synaptics optical sensor embedded in the OLED display, letting users unlock by touching a designated area on the screen. The phone was a limited-edition variant of the standard X20 Plus, sold mainly in China, and it paved the way for the mainstream adoption of under-display fingerprint technology.

Background: Why the X20 Plus UD Mattered

In early 2018, almost every phone with a fingerprint reader placed the sensor on the front bezel, the back, or the side. The dream of a full-screen phone with no visible fingerprint sensor seemed impossible because the sensor needed to read the ridge pattern of your finger through the display glass. Vivo, a Chinese brand known for pushing camera and audio features, partnered with Synaptics to produce the world’s first commercial phone with an optical in-display sensor. The X20 Plus UD was announced at CES 2018 and went on sale in China later that month.

The phone was essentially the Vivo X20 Plus (released late 2017) with one key difference: the fingerprint sensor moved from the back to the front under the OLED screen. Vivo had to redesign the internal layout to fit the sensor module, and the company released a separate model number (X20 Plus UD) to distinguish it from the regular X20 Plus. The launch was a proof-of-concept for the industry, and within a year, many other brands followed with their own in-display sensors.

How the In-Display Fingerprint Sensor Worked

The X20 Plus UD used an optical fingerprint sensor, not the ultrasonic type that later phones (like the Galaxy S10) would use. The optical method works like this:

The OLED screen emits light from the pixels in the area where your finger rests.
That light reflects off the ridges and valleys of your fingerprint.
A tiny image sensor placed directly under the display captures the reflected light pattern.
The phone’s processor compares that pattern to the stored fingerprint data and unlocks if it matches.

Because the sensor needed light to pass through the display, it only worked with OLED panels (LCDs are too thick and opaque). The sensor area was a small circle at the bottom of the screen, visible only when you pressed on it—the phone illuminated a fingerprint icon to show you where to place your finger. The technology was slower and less reliable than traditional capacitive sensors, but it worked and proved the concept.

Specifications and Pricing of the X20 Plus UD

The X20 Plus UD shared most specs with the standard X20 Plus. Here’s what you got for the price (around 3,598 RMB in China, roughly $560 at the time):

6.43-inch Super AMOLED display, 1080 x 2160 resolution
Qualcomm Snapdragon 660 processor
4GB RAM and 128GB storage (expandable via microSD)
Dual rear cameras: 12MP main (f/1.8) + 5MP depth sensor
12MP front camera with face unlock
3,905 mAh battery with fast charging
Android 7.1.1 (Nougat) with Funtouch OS 3.2

The phone was sold only in China, with no official international release. That limited its audience, but tech enthusiasts who imported it got a glimpse of the future. The standard X20 Plus continued to sell alongside it, and the UD variant was produced in relatively small numbers.

Comparing the X20 Plus UD to Later In-Display Sensors

If you’re curious how the first in-display sensor holds up against modern ones, the difference is night and day. The X20 Plus UD’s sensor was:

Slower: Unlock took about 0.7 seconds, while modern sensors take 0.2-0.3 seconds.
Less reliable: It failed to recognize fingerprints roughly 1 in 10 times, especially if your finger was wet or the screen had a thick protector.
Smaller area: The sensor region was a small circle, whereas newer phones offer larger, more forgiving areas.
Limited to one finger? Actually, it could store multiple fingerprints, but you had to press precisely on the circle.

Modern in-display sensors (both optical and ultrasonic) are faster, larger, and more accurate. Ultrasonic sensors, like those in the Galaxy S21 and later, use sound waves to map the fingerprint in 3D, which works better with wet fingers and doesn’t rely on screen brightness. But the X20 Plus UD’s optical approach is still the basis for most budget and mid-range phones today because it’s cheaper to produce.

Common Problems and Misconceptions

Owners of the X20 Plus UD reported a few common issues that you might still encounter if you buy a used unit or a similar early in-display sensor phone:

Screen protector interference: Thick glass protectors blocked the sensor’s light, causing frequent failures. Only thin film protectors worked reliably.
Fingerprint registration issues: The sensor required you to press harder than usual during setup, and some users found that re-registering the same finger multiple times improved accuracy.
Battery drain: The screen had to light up the sensor area each time you unlocked, which added a small drain compared to a back-mounted sensor.
Misconception that it scans your fingerprint through the entire screen: No, only the small designated circle works.

Another misconception is that the X20 Plus UD was the first phone with an in-display sensor ever. In fact, Vivo showed a prototype at MWC 2017, and there were earlier concept phones, but the X20 Plus UD was the first to go on sale to the public.

Why the X20 Plus UD Was a Turning Point

The launch of the X20 Plus UD proved that in-display fingerprint sensors were commercially viable. Within months, Vivo released the X21 and NEX series with improved in-display sensors, and by the end of 2018, OnePlus, Huawei, and Xiaomi had all adopted the technology. By 2019, under-display sensors were standard on most premium phones, and they’ve since trickled down to budget devices. The X20 Plus UD’s legacy is that it pushed the industry away from bezels and notches, enabling the full-screen designs we see today.

For collectors, the X20 Plus UD is a piece of history. It’s not a great daily driver by modern standards—the Snapdragon 660 is slow, and the camera is mediocre—but it’s a fascinating device to own and show off. If you find one on a second-hand marketplace, expect to pay anywhere from $100 to $200 depending on condition, and be prepared for the sensor’s quirks.

Frequently Asked Questions

Is the Vivo X20 Plus UD the first phone with an in-display fingerprint sensor?

Yes, it was the first commercially available smartphone with an in-display fingerprint sensor. It went on sale in China in January 2018, beating all competitors to market. Vivo had shown prototypes earlier, but the X20 Plus UD was the first you could actually buy.

Does the X20 Plus UD work with screen protectors?

It works with thin film protectors, but thick glass protectors will block the sensor. Vivo recommended using the official film protector that came in the box. If you use a glass one, you’ll likely experience frequent unlock failures. Modern in-display sensors are more tolerant, but this early model was picky.

What is the difference between the X20 Plus and the X20 Plus UD?

The only difference is the fingerprint sensor. The standard X20 Plus has a rear-mounted fingerprint sensor, while the UD variant has the sensor under the display. Everything else—processor, camera, battery, screen—is identical. The UD version was also slightly heavier and thicker due to the sensor module.

Can I use the X20 Plus UD outside China?

Yes, but you’ll need to check network bands. The phone supports GSM, CDMA, and some LTE bands used in China, but it may not support all 4G bands in other countries. It also comes with Chinese software (Funtouch OS) which has no Google Play store pre-installed, though you can sideload Google apps. For most users outside China, it’s not a practical daily phone.

Why did Vivo stop selling the X20 Plus UD?

It was a limited-edition launch to showcase the technology. Vivo produced a small batch to test the market and gather feedback. After the X20 Plus UD, they released the X21 with a second-generation in-display sensor, which was sold in larger quantities. The X20 Plus UD was never meant to be a high-volume product.

Is the in-display fingerprint sensor on the X20 Plus UD safe to use?

Yes, it’s as secure as any fingerprint sensor. It stores a mathematical representation of your fingerprint, not the image itself, and the data is encrypted on the phone. The optical sensor can be fooled by a high-quality 3D-printed fingerprint, but that’s true of most fingerprint sensors. For everyday use, it’s safe.

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