What kind of oscillator circuit technology is used for 5G technology?
The frequency is indeed out of range of a crystal oscillator. But you don't need a crystal to generate your fundamental directly. In fact, all previous frequency bands used in 2G/3G/4G are also out of range of these crystals. 

The trick is to use a PLL. Modern CMOS circuit technologies can product fundamental oscillators past 150 GHz* - making one that oscillates at 30-40 GHz is not that difficult. You then use some kind of divider/mixer/counter to compare it with the crystal or MEMS oscillator that might be at 100 MHz or lower, and use the result to tweak the oscillating frequency of your high-frequency oscillator. 
The added advantage of this is that by tweaking the divider ratio, you can change the frequency of the high-frequency oscillator (for example to switch to a different channel), without needing a different reference. 

*That was with planar CMOS, don't know how finfet performs since it's Ft/Fmax is generally lower than planar/FD-SOI