  The Lumped Element Kinetic Inductance Detectors (LEKID)demonstrated full
maturity in the NIKA (New IRAM KID Arrays)instrument. These results allow
directly comparing LEKID performance with other competing technologies (TES,
doped silicon) in the mm and sub-mm range. A continuing effort is ongoing to
improve the microfabrication technologies and concepts in order to satisfy the
requirements of new instruments. More precisely, future satellites dedicated to
CMB (Cosmic Microwave Background) studies will require the same focal plane
technology to cover, at least, the frequency range of 60 to 600 GHz. Aluminium
LEKID developed for NIKA have so far demonstrated, under real telescope
conditions, performance approaching photon-noise limitation in the band 120-300
GHz. By implementing superconducting bi-layers we recently demonstrated LEKID
arrays working in the range 80-120 GHz and with sensitivities approaching the
goals for CMB missions. NIKA itself (350 pixels) is followed by a more
ambitious project requiring several thousands (3000-5000) pixels. NIKA2 has
been installed in October 2015 at the IRAM 30-m telescope. We will describe in
detail the technological improvements that allowed a relatively harmless
10-fold up-scaling in pixels count without degrading the initial sensitivity.
In particular we will briefly describe a solution to simplify the difficult
fabrication step linked to the slot-line propagation mode in coplanar
waveguide.
