Ground-based microlensing surveys enable us to detect planets down to Earth masses
beyond the snow line, where temperature is cold enough for ices to condense. These cold,
small planets (less massive ones than Saturn mass) are hard to find by the other
detection methods, such as, transit, radial velocity and direct imaging. Thus, it is
crucial to study planet distribution from microlensing survey to understand planet
formation mechanism.

In this talk, I will present the discovery of a break in the exoplanet mass ratio
function beyond the snow line from the statistical analysis of a microlensing survey
data. The peak of the mass ratio function is at q~1.7¡ß10-4, which is about Neptune mass
if the host star is an M-type star. We use Microlensing Observations in Astrophysics
(MOA) survey data in 2007-2012, including 22 planetary events and 1 ambiguous event with
possible planetary and stellar binary solutions, to estimate the planet frequency as a
function of the planet/star mass ratio and separation relative to the Einstein
radius. This study implies that Neptunes and failed Jupiter cores are the most common
type of planets beyond the snow line. Also, I will briefly introduce future microlensing
surveys: PRIME and WFIRST.