The Silicon Electron Multiplier sensor

The Silicon Electron Multiplier (SiEM) is a novel sensor concept for minimum ionising 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, SPADs), 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<math display="inline" id="d1e533" altimg="si3.svg"><msup><mrow/><mrow><mn>16</mn></mrow></msup></math> n<math display="inline" id="d1e541" altimg="si4.svg"><msub><mrow/><mrow><mi mathvariant="normal">eq</mi></mrow></msub></math>/cm<math display="inline" id="d1e549" altimg="si5.svg"><msup><mrow/><mrow><mn>2</mn></mrow></msup></math>. 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 6–15µm. 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.