  The Silicon Electron Multiplier (SiEM) is a novel sensor concept for minimum
ionizing particle (MIP) detection which uses internal gain and fine pitch to
achieve excellent temporal and spatial resolution. In contrast to sensors where
the gain region is induced by doping (LGADs, APDs), amplification in the SiEM
is achieved by applying an electric potential difference in a composite
electrode structure embedded within the silicon bulk using MEMS fabrication
techniques. Since no gain-layer deactivation is expected with radiation damage,
such a structure is expected to withstand fluences of up to $10^{16} n_{eq}$.
Various geometries and biasing configurations are studied, within the
boundaries imposed by the fabrication process being considered. The effective
gain, the field in the sensor, the leakage current and breakdown conditions are
studied for cell sizes in the range of $6 - 15 \mu m$. Simulations show that
gains in excess of 10 can be achieved, and studies of the time structure of the
induced signals from a charge cloud deposited in the middle of the sensor show
that time resolutions similar to other sensors with internal gain can be
expected. Plans for the manufacture of a proof-of-concept sensor and for its
subsequent characterisation are discussed.
