  In 2008, a triple GEM detector prototype with an area of ~2000 cm2 has been
constructed, based on foils of 66*66 cm. GEMs of such dimensions had not been
made before, and innovations to the existing technology were introduced to
build this detector. This paper discusses these innovations and presents
further work on large area GEM development.
  A single-mask technique overcomes the cumbersome practice of alignment of two
masks, which limits the achievable lateral size. The holes obtained with this
technique are conical, and have a so-called rim, a small insulating clearance
around the hole in the substrate. Further refinements of this technique allow
greater control over the shape of holes and the size of rims. Also, an
improvement in homogeneity over large areas is expected.
  Simulation studies have been done to examine the effect of hole shape on the
behavior of GEMs. Such studies can help understanding how to use new
enhancements of the technique to optimize performance.
  Many potential applications for large area GEMs foresee large production
volumes. Production issues have been studied, and single-mask GEMs turn out to
be much more suitable for large scale production than standard GEMs.
