  This paper describes a temperature sensitivity or thermal sag measurement of
a geometric anti-spring based micro-electromechanical system (MEMS) gravimeter
(Wee-g). The Wee-g MEMS gravimeter is currently fabricated on a (100) silicon
wafer using standard micro-nano fabrication techniques. The thermal behavior of
silicon indicates that the Young's modulus of silicon decreases with an
increase in temperature (around 63 ppm/K). This leads to a softening of the
silicon material resulting in the proof mass (PM) displacing (or sagging) under
the influence of an increasing temperature. It results in the change on the
measured gravity and it is expressed as a temperature sensitivity in terms of
change in gravity per degree temperature. The temperature sensitivity for the
silicon based MEMS gravimeter is found to be 60.14-64.87 muGal/mK, 61.76
muGal/mK and 62.76 muGal/mK for experimental, finite element analysis (FEA)
simulation and analytical calculations respectively. It suggests that
temperature sensitivity is depended on material properties used to fabricate
the MEMS devices. In this paper the experimental measurements of thermal sag
are presented, along with analytical calculations and simulations of the effect
using FEA (finite element analysis). The bespoke optical measurement system to
quantify the thermal sag is also described. The results presented are an
essential step towards the development of temperature insensitive MEMS
gravimeters.
