  The Gas Electron Multiplier (GEM) manufacturing technique has recently
evolved to allow the production of large area GEMs. A novel approach based on
single mask photolithography eliminates the mask alignment issue, which limits
the dimensions in the traditional double mask process. Moreover, a splicing
technique overcomes the limited width of the raw material. Stretching and
handling issues in large area GEMs have also been addressed. Using the new
improvements it was possible to build a prototype triple-GEM detector of ~ 2000
cm2 active area, aimed at an application for the TOTEM T1 upgrade. Further
refinements of the single mask technique give great control over the shape of
the GEM holes and the size of the rims, which can be tuned as needed. In this
framework, simulation studies can help to understand the GEM behavior depending
on the hole shape.
