Details of Samsung's Galaxy S21 have leaked, and thanks to Ice Universe and FCC documents (via Slashleaks), we know how the fingerprint sensor under the display has been improved, as well as the phone's size.

According to this FCC document, the diagonal dimension of the display is 158 mm, which translates to 6.22 inches, making this model the smallest of the S21 family, the basic Galaxy S21. The Galaxy S21 Plus is expected to be 6.7" and the S21 Ultra 6.8".

Other included dimensions are height and width, 151.6 x 71 mm; compared to the Galaxy S20's 151.7 x 69.1 mm, the S21 is slightly taller and wider, but not significantly different; the S21 is slightly taller and wider, but the phone's thickness is not stated, so we cannot compare them yet.

We also learned from this FCC filing that the S21 will use the Snapdragon 888 chipset. International Galaxy S21 buyers may notice that the S21 uses Samsung's own chipset, the Exynos 2100.

Meanwhile, leaker Ice Universe revealed interesting information about the under-display ultrasonic fingerprint scanner the S21 will use, which at 8 x 8 mm is apparently 1.77 times larger than the sensor used in the S20, the same sensor that debuted in the Galaxy S10 in 2019 . Even better, the sensor is said to be twice as fast and seems to work with a tap rather than a sustained press.

While definitely not as futuristic and easy to use as Apple's Face ID, the ultrasonic fingerprint sensor used by Samsung may be preferable for many users who find it more convenient to scan their finger or thumb than to hold the phone to their face. Furthermore, many people still wear masks when out in public, so scanning fingers may be more convenient.

In theory, ultrasonic sensors outperform the standard optical sensors that most android manufacturers use in similar under-display readers. Because they operate on sound rather than light, Samsung's sensors can continue to work even if the display is scratched.

Rumors suggest that official details of the Galaxy S21 series will be announced in January, with a launch event possibly taking place on January 14; the S21 Ultra will feature a 108MP main camera and two 10MP telephoto cameras with 3x and 10x optical zoom.